Introduction
Veterinarians are routinely presented with juvenile dogs for elective OHE or castration and must assess each dog's health status to determine whether a dog is healthy enough to undergo anesthesia and surgery. According to the American Animal Hospital Association's Anesthesia and Monitoring Guidelines,1 anemia is an anesthetic risk factor for which corrective intervention is advisable; thus, many veterinarians perform presurgical PCVs or CBCs in dogs.1 However, RIs from diagnostic laboratories are established with results from adult animals, and RIs for adult dogs might not apply to juvenile dogs.
The largest data set available on hematologic values for juvenile dogs is from a research colony of 500 healthy Beagles and provides RIs for PCV, MCV, and MCHC in dogs up to 1 year of age.2 Additional studies have evaluated hematologic parameters in healthy Beagle and Borzoi puppies ≤ 60 days of age3,4,5 and mixed-breed dogs and Labrador Retrievers that were between 16 and 60 days of age.6 These studies2,3,5 show that, compared with a laboratory RI for PCV in adult dogs (PCV, 40% to 57%), newborn puppies have a similar mean PCV of 46% to 50% but that the mean PCV in puppies declines by 1 month of age (28% to 33%), then increases by 3 months of age (41%) and is again within adult RI limits by 6 months of age (48%). A similar pattern is seen in studies4,6 that show newborn puppies have a median cHct of 39%, which is below but near the adult RI for cHct (41% to 59%), and that the median cHct declines in puppies by 1 month of age (23% to 28%), then increases by 2 months of age (32%).
It is unknown whether established hematologic RIs for adult dogs are applicable when evaluating juvenile dogs from shelters (shelter dogs) with unknown histories and potential comorbidities. Without preventative care, shelter dogs might be more prone to infectious diseases; however, thorough diagnostic testing to determine each shelter dog's health status is not always feasible owing to financial limitations. Because neutering is best performed before adoption, it is important to proceed with the surgery in shelter dogs whenever possible.7 Thus, a better understanding of clinically normal hematologic parameters in juvenile shelter dogs, acknowledging typical comorbidities, is warranted and may guide veterinarians in making diagnostic and presurgical decisions for these dogs.
The objective of the study reported here was to compare results for hematologic parameters (PCV, cHct, MCV, MCHC, and reticulocyte count) for juvenile versus adult shelter dogs that outwardly appeared healthy and were presented for elective OHE or castration. We hypothesized that although juvenile shelter dogs might have comorbidities that could cause mild anemia, they would have lower PCV and cHct values than would adult shelter dogs and would have a similar pattern for PCV and cHct results during early life as previously reported2,3,4,5,6 for healthy research and breeding colony dogs. We also hypothesized that elective OHE or castration in juvenile shelter dogs would rarely need to be postponed because of results for PCV or cHct below the RIs for adult dogs, even when comorbidities are considered.
Materials and Methods
Animals
Dogs eligible for this prospective study were presented from various local animal shelters to the Kansas State University College of Veterinary Medicine for elective OHE or castration by veterinary students in the Veterinary Surgery course between October 7 and December 6, 2019. The shelters were asked to send only dogs that were healthy and considered good candidates for anesthesia and to provide a medical history for each dog, recognizing that the histories of shelter dogs are often incomplete. Participating shelters provided informed consent for physical, hematologic, fecal, and radiographic examinations; general anesthesia; and surgery for each dog before enrollment. The study protocols were reviewed and approved by the university's institutional animal care and use committee.
Patient assessments
Physical examination—On arrival at Kansas State University, each dog underwent a complete physical examination, including the use of a flea comb to assess for the presence of fleas or flea dirt. Although age estimates were provided by the shelters, the age range of each dog was also estimated on the basis of dental eruption characteristics8 identified during an oral examination performed by the research team (KSK and JBK). Dogs for which the age determined by dental assessment did not match the estimated age reported by the shelter were reexamined, and findings were discussed by the research team to finalize the age group assignment. Dogs with no adult incisors erupted were estimated to have been < 3 months of age, dogs with ≥ 1 erupted adult incisor tooth but ≤ 3 erupted adult canine teeth were estimated to have been ≥ 3 to ≤ 6 months of age, and dogs with complete eruption of all 4 canine teeth were estimated to have been > 6 months of age. Additionally, dogs ≤ 6 months of age were categorized as juveniles, and dogs > 6 months of age were categorized as adults.
Hematologic assessments—Also on the day of arrival, each dog underwent jugular or lateral saphenous vein phlebotomy with a 20- to 23-gauge needle attached to a 3- to 5-mL nonheparinized syringe to collect 2 mL of blood that was then transferred to an evacuated plastic tube with an EDTA additive. A PCV and CBC were performed, and a testa was performed to assess for Dirofilaria immitis antigen and Ana-plasma phagocytophilum, Borrelia burgdorferi, and Ehrlichia canis antibodies. Third-year veterinary students measured the PCVs by transferring a portion of each blood sample from the evacuated tube into 100-µL plain microhematocrit tubes (2 tubes/dog) that were then centrifuged at 5,900 × g for 5 minutes; then the students used preprinted microhematocrit cardsb with every 1% indicated to determine the PCV in each microhematocrit tube. Whole blood samples in evacuated tubes with EDTA additive were submitted to the Kansas State Veterinary Diagnostic Laboratory for hematologic assessments with a commercial analyzer.c Results for cHct, MCV, MCHC, and absolute reticulocyte count were recorded for each dog. The cHct was determined with the formula cHct = (MCV × RBC count)/10, where the RBC count is the erythrocyte concentration as millions of RBCs per µL.
Fecal tests—Dogs with soft feces or diarrhea had fecal samples collected for fecal flotation assessments performed by third-year veterinary students. Dogs with lethargy, vomiting, bloody diarrhea, or leukopenia, alone or in combination, were evaluated for the presence of parvovirus antigen with a kennel-side test.d
Treatment decisions
Dogs with no overt evidence of anesthetic or surgical contraindications on the basis of findings from physical examination and other assessments subsequently underwent elective OHE or castration performed by third-year veterinary students under close supervision by faculty anesthesiologists and surgeons. Afterward, dogs were provided appropriate postoperative analgesia and monitoring, then were returned to their shelters 3 days postoperatively. Dogs with identified abnormalities preventing anesthesia and surgery were treated medically in consultation with their shelter.
Statistical analysis
Descriptive statistics were used to summarize results for demographic information and diagnostic tests. A 1-way ANOVA with a post hoc Tukey test was used to compare hematologic results for PCV, cHct, MCV, MCHC, and reticulocyte count across age groups. The χ2 test was used to compare proportions of dogs in age groups with results above, within, or below adult RIs. A paired t test was used to compare results for PCV versus cHct for each age group, and an independent Student t test was used to compare hematologic results for juvenile versus adult dogs and for male versus female dogs within each age group. A 1-way ANOVA was repeated after results for dogs with identified infectious diseases or parasitism were removed from the data set. Statistical analysise and figure creationf were performed with available software, and values of P ≤ 0.05 were considered significant.
Results
Animals
There were 138 dogs enrolled from 13 regional shelters, 2 with and 11 without attending veterinarians who examined dogs before referral. On the basis of dental eruption characteristics, there were 56 juvenile dogs, including 34 dogs (18 males and 16 females) < 3 months of age and 22 dogs (8 males and 14 females) ≥ 3 to ≤ 6 months of age. There were 82 dogs (35 males and 47 females) > 6 months of age, which were classified as adults. Of the 77 female dogs, 73 were sexually intact, and 4 (all in the adult group) were determined at surgery to have been spayed previously. Mixed-breed dogs (n = 90) were most common, followed by Chihuahuas (8), Labrador Retrievers (7), German Shepherd Dogs (5), Border Collies (4), Wheaton Terriers (3), Australian Cattle Dogs (3), Great Danes (2), and 1 each of 16 other breeds. Dogs in each age group had a good distribution of shelters represented, with 6 shelters represented in the group of dogs < 3 months of age, 8 shelters represented in the group of dogs ≥ 3 to ≤ 6 months of age, and 12 shelters represented in the group of dogs > 6 months of age.
Information about prior anthelminthic or flea prevention treatment was provided from the shelters for 128 of the 138 (93%) dogs (32 dogs < 3 months old, 19 dogs ≥ 3 to ≤ 6 months old, and 77 dogs > 6 months old). Anthelminthic medication had been administered ≤ 2 weeks before enrollment for 51 of the 128 (40%) dogs (12/32 [38%] dogs < 3 months old; 8/19 [42%] dogs ≥ 3 to ≤ 6 months old, and 31/77 [40%] dogs > 6 months old). Flea prevention treatment had been administered to 65 of the 128 (51%) dogs (16/32 [50%] dogs < 3 months old, 13/19 [68%] dogs ≥ 3 to ≤ 6 months old, and 36/77 [47%] dogs > 6 months old). The products and doses varied among shelters.
Hematologic data
Complete hematologic data were available for 123 of the 138 (89%) dogs (32 dogs < 3 months old, 21 dogs ≥ 3 to ≤ 6 months old, and 70 dogs > 6 months old). For the remaining 15 dogs (2 dogs < 3 months old, 1 dog ≥ 3 to ≤ 6 months old, and 12 dogs > 6 months old), the absolute reticulocyte counts were missing because the main hematologic analyzer underwent maintenance during a week of the study and the replacement analyzerg did not provide reticulocyte counts.
PCV and cHct—Mean PCV and cHct were significantly (P = 0.001) lower for each age group of juvenile dogs (35.8% and 35.6%, respectively, for dogs < 3 months old, and 37.6% and 37.0%, respectively, for dogs ≥ 3 to ≤ 6 months old), compared with adult dogs (44.9% and 45.8%, respectively; Figure 1). Further, the mean PCV and cHct were significantly (P < 0.001) lower for all juvenile dogs collectively (36.5% and 36.1%, respectively) versus adult dogs. The proportion of dogs with results below the lower limit of the RI for cHct was significantly (P < 0.001) higher for juvenile dogs < 3 months old (31/34 [91%]) and those ≥ 3 to ≤ 6 months old (19/22 [86%]), compared with adult dogs (11/82 [13%]; Table 1).
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Individual-value plots of PCV (A), cHct (B), MCV (C), MCHC (D), and absolute reticulocyte count (E) results for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age group. In each plot, each circle represents a result for an individual dog; the horizontal line across the center of the error bars represents the mean, and the horizontal lines at the upper and lower ends of the error bars represent the SD. For panels A through D, the upper and lower horizontal dashed lines represent the upper and lower limits of the RIs in adult dogs. For panel E, the horizontal dashed line represents the upper limit of the laboratory RIs. *Results differed significantly (P < 0.05), compared with those for adult dogs (> 6 months of age). †Results differed significantly (P < 0.05), compared with those for juvenile dogs < 3 months of age.
Citation: Journal of the American Veterinary Medical Association 259, 3; 10.2460/javma.259.3.275
Results of χ2 tests to compare proportions of hematologic results (PCV, cHct, MCV, MCHC, and reticulocyte count) that were below, above, or within laboratory RIs for 138 shelter dogs that were presented for routine OHE or castration between October 7 and December 6, 2019, stratified by age groups: adult (> 6 months of age) and juvenile (< 3 months of age or ≥ 3 to ≤ 6 months of age).
| Parameter | RI for adult dogs | Juvenile shelter dogs (n = 56) | χ2 | P value | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| < 3 months old (n = 34) | ≥ 3 to ≤ 6 months old (n = 22) | Adult shelter dogs (n = 82) | |||||||||||||
| Mean (range) | No. (%) of dogs | Mean (range) | No. (%) of dogs | Mean (range) | No. (%) of dogs | ||||||||||
| Results below RI | Results within RI | Results above RI | Results below RI | Results within RI | Results above RI | Results below RI | Results within RI | Results above RI | |||||||
| PCV (%) | 40–57 | 35.8 (28–48) | 29 (85) | 5 (15) | 0 (0) | 37.6 (30–47) | 14 (64) | 8 (36) | 0 (0) | 44.9 (32–59) | 12 (15) | 69 (84) | 1 (1) | 56.4 | < 0.0001 |
| cHct (%) | 41–59 | 35.6 (27–46) | 31 (91) | 3 (9) | 0 (0) | 37.0 (3I-48) | 19 (86) | 3 (14) | 0 (0) | 45.8 (34–59) | 11 (13) | 71 (87) | 0 (0) | 77.8 | < 0.0001 |
| MCV (fL) | 64–76 | 66.4 (60.8–72.9) | 8 (24) | 26 (76) | 0 (0) | 67.1 (59.6–70.1) | 2 (9) | 20 (91) | 0 (0) | 67.4 (57.3–74.5) | 13 (16) | 69 (84) | 0 (0) | 2.1 | 0.349 |
| MCHC (g/dL) | 33–36 | 33.1 (28.0–38.6) | 15 (44) | 17 (50) | 2 (6) | 34.0 (3I.8–39.0) | 3 (14) | 17 (77) | 2 (9) | 34.7 (30.2–38.8) | 2 (2) | 68 (83) | 12 (15) | 34.1 | < 0.0001 |
| Reticulocytes (cells X 10'/|L)* | < 0.100 | 0.I35 (0.050–0.240) | 4 (13) | 0 (0) | 28 (88) | 0.100 (0.040–0.200) | 12 (57) | 0 (0) | 9 (43) | 0.068 (0.010–0.180) | 60 (86) | 0 (0) | 10 (I4) | 50.1 | < 0.0001 |
Results reported for 123 of the 138 dogs (32 dogs < 3 months old, 21 dogs ≥ 3 to ≤ 6 months old, and 70 dogs > 6 months old [adult group]) because the main hematologic analyzer underwent maintenance during a week of the study and the replacement analyzer did not provide reticulocyte counts for samples (from 2 dogs < 3 months old, 1 dog ≥ 3 to ≤ 6 months old, and 12 dogs > 6 months old) assessed during that period.
When results for PCV and cHct were considered within age groups, findings for the adult group indicated that the mean PCV (44.9%) was significantly (P = 0.004) lower than the mean cHct (45.8%). There was no statistical difference between the mean PCV and mean cHct within juvenile dogs < 3 months old (P = 0.673) or those ≥ 3 to ≤ 6 months old (P = 0.500).
When dogs in each age group were further grouped by sex, the mean cHct was significantly (P = 0.023) lower for male (34.1%) versus female (37.3%) dogs < 3 months old. However, the mean cHct did not differ substantially (P = 0.463 and P = 0.910, respectfully) between male (37.8%) and female (36.6%) dogs ≥ 3 to ≤ 6 months old or between male (45.7%) and female (45.8%) dogs > 6 months old.
MCV, MCHC, and reticulocyte count—Mean MCV did not substantially (P = 0.38) differ across age groups. However, the mean MCHC was significantly (P < 0.001) lower for dogs < 3 months old (33.1 g/dL) versus dogs > 6 months old (34.7 g/dL; Figure 1). The mean reticulocyte count was significantly (P = 0.006 and P = 0.002, respectively) higher for dogs < 3 months old (135,000 reticulocytes/µL) versus those ≥ 3 to ≤ 6 months old (100,000 reticulocytes/µL) and for dogs ≥ 3 to ≤ 6 months old versus > 6 months old (68,000 reticulocytes/μL). No substantial differences were detected in proportions of dogs in each age group with results above, within, or below the limits for the RI for MCV (P = 0.349); however, dogs < 3 months old had the highest proportion with results below the lower limit of the RI for MCHC (15/34 [44%]; P < 0.001) and the highest proportion with results above the upper limit of the RI for the reticulocyte count (28/32 [88%]; P < 0.001; Table 1).
When dogs in each age group were further considered by sex, the mean reticulocyte count was significantly (P = 0.017) higher for female (155,000 reticulocytes/μL) versus male (118,000 reticulocytes/μL) dogs < 3 months old; however, this group had no substantial (P = 0.615 and P = 0.254, respectively) differences detected in the mean MCV or MCHC for females (66.2 fL and 32.8 g/dL) versus males (66.7 fL and 33.5 g/dL). Further, no substantial differences were detected in the mean MCV, MCHC, or reticulocyte count for males versus females in either of the older groups.
Parasitism and infection
Twenty-seven of the 138 (19.6%) dogs had evidence of parasitism or infections identified on the day of presentation (Table 2). Dogs with flea dirt or live fleas (12/138 [8.7%]) received a single oral dose of nitenpyram,h a bath with medicated shampoo, or both.
Hematologic results for the 27 shelter dogs that tested positive for various parasitic or infectious agents (alone or in combination) from among the 138 shelter dogs described in Table 1.
| Infectious agent or parasite | Overall | By age group | PCV (%)* | cHct (%)* | MCV (fL)* | MCHC (g/dL)* | Reticulocyte count (cells X 106/μL)* | |
|---|---|---|---|---|---|---|---|---|
| No (%) of dogs | Age group | No. of dogs | ||||||
| Fleas or flea dirt | 12 (8.7) | > 6 mo | 10 | 43 (39–48) | 43 (37–47) | 67 (60–75) | 35 (30–39) | 0.083 (0.020–0.180) |
| ≥ 3 to ≤ 6 mo | 1 | 35 | 37 | 66.8 | 33 | 0.200 | ||
| < 3 mo | 1 | 33 | 30 | 62.9 | 39 | — | ||
| Anaplasma phagocytophilum | 4 (2.9) | > 6 mo | 4 | 45 (37–53) | 45 (36–56) | 66 (64–69) | 35 (34–38) | 0.I03 (0.090–0.I20) |
| Ehrlichia canis | 4 (2.9) | > 6 | 3 | 43 (40–45) | 43 (40–47) | 64 (60–67) | 36 (35–38) | 0.030 (0.030–0.030) |
| Toxocara | 3 (2.2) | < 3 mo | 3 | 29 (28–3I) | 30 (27–34) | 65 (6I-68) | 30 (28–32) | 0.I70 (0.I00–0.240) |
| Ancylostoma | 2 (1.4) | > | 1 | 35 | 35 | 68 | 32 | 0.110 |
| < 3 mo | 1 | 29 | 29 | 67 | 32 | 0.100 | ||
| Taenia | 1 (0.7) | < 3 mo | 1 | 35 | 35 | 68 | 33 | 0.I50 |
| Coccidia | 1 (0.7) | ≥ 3 to ≤ 6 mo | 1 | 37 | 37 | 67 | 32 | 0.070 |
| Parvovirus | 1 (0.7) | < 3 mo | 1 | 43 | 40 | 63 | 35 | 0.050 |
| Heartworm | 1 (0.7) | > 6 mo | 1 | 49 | 50 | 65 | 34 | 0.070 |
Results reported as mean and range when multiple dogs were affected.
— = Not measured.
One dog with no history of coughing tested positive for heartworm antigen and thus underwent thoracic radiography for further preanesthetic risk assessment9; radiographic findings were unremarkable, and the dog was considered to be an acceptable candidate to proceed with surgery as scheduled. Dogs that tested negative for heartworm antigen (n = 137) received 1 dose of a heartworm preventativei,j,k administered per FDA-approved label instructions. The heartworm preventative administered depended on product availability during the study period.
No dog had antibodies against B burgdorferi. Four dogs had antibodies against E canis; however, none of these 4 dogs were febrile or thrombocytopenic (range, 206,000 to 280,000 platelets/μL; RI, 130,000 to 370,000 platelets/μL). Four dogs, all afebrile, had antibodies against A phagocytophilum, and 1 of these dogs (an adult female mixed breed) had thrombocytopenia (51,000 platelets/μL) without anemia (PCV, 44%). This dog's surgery was postponed, and antimicrobial treatment (doxycycline; 4.2 mg/kg [1.9 mg/lb], PO, q 12 h for 21 days) for anaplasmosis was initiated.
Fourteen dogs had soft feces or diarrhea, and samples were tested by fecal flotation. Parasites were identified in the fecal samples of 6 of the 14 (43%) dogs (Toxocara alone [n = 2], Toxocara and Ancylostoma [1], Ancylostoma alone [1], Taenia alone [1], or coccidia alone [1]). All 138 dogs received an antihelminthicl that was administered per FDA-approved label instructions, and the single dog with coccidiosis was also treated with ponazurilm (30 mg/kg [13.6 mg/lb], PO, q 24 h for 3 days). Three of the 14 dogs had lethargy, vomiting, bloody diarrhea, or leukopenia (alone or in combination) and were tested for parvovirus antigen; 1 dog (a male mixed-breed dog < 3 months old) had positive test results yet no concurrent anemia (PCV, 43%). The surgery for this dog was postponed, and the dog was treated medically in isolation.
The 1-way ANOVA with post hoc Tukey test was repeated after results for the 27 dogs with evidence of parasitism or infection were removed from the data set. Findings indicated similar significant (P < 0.001) associations between age and results for PCV, cHct, MCHC, and reticulocyte count for all 138 dogs and for only the 111 dogs without evidence of parasitism or infection. Another commonality was that findings indicated no meaningful association between age and results for MCV when results for all 138 dogs were considered (P = 0.38) and when results for only the 111 dogs without evidence of parasitism or infection were considered (P = 0.51). However, when results for only the 111 dogs without evidence of parasitism or infection were considered, the mean MCHC was significantly (P = 0.017) higher for juvenile dogs ≥ 3 to ≤ 6 months old (34.3 g/dL) versus those < 3 months old (33.2 g/dL).
Overall, 136 of the 138 (98.6%) shelter dogs underwent OHE or castration as scheduled, and none had anesthetic, surgical, or postoperative complications related to findings on preoperative hematologic assessments. Three days after surgery, all dogs were discharged to the shelters from where they came. The shelters were informed of diagnostic test results and treatments administered and were provided with recommendations for follow-up care.
The 1 dog with thrombocytopenia and anaplasmosis recovered with treatment, had a platelet count of 293,000 platelets/μL, and underwent OHE 5 weeks later than originally scheduled, then became available for adoption. The 1 dog with parvovirus infection recovered and was discharged after 2 days, had an uneventful castration 2 months later, and then was adopted.
Discussion
Results of the present study supported our hypothesis that the mean PCV and cHct would be lower for juvenile shelter dogs (≤ 6 months of age), compared with adult shelter dogs (> 6 months of age) and the lower limits of current laboratory RIs. As hypothesized, although some dogs did have infectious comorbidities that could have contributed to anemia, our findings indicated that they had similar hemato-logic values as those seen in healthy juvenile dogs from research and breeding colony populations.2,3,4,5,6 Although 27 of the 138 (19.6%) dogs in the present study had parasitism or infection identified, no dog had surgery postponed because of their PCV or cHct values or concern about anemia. All but 2 dogs (136/138 [98.6%]) were determined healthy enough to safely proceed with elective OHE or castration, which is a primary goal of shelter medicine and increases the adoptability of dogs.
Although hematologic results for dogs in the present study had a similar pattern to that documented in previous studies2,3,4,5,6 of dogs with known histories, the differences in results for juvenile dogs (≤ 6 months old) versus adult dogs (> 6 months old) appeared more pronounced in the shelter dogs we evaluated. We recognize that the present study was limited by our not knowing each dog's exact age and that this issue makes direct comparisons between studies challenging; however, the use of dental eruption characteristics to estimate age, as we did in the present study, is commonly accepted.8 Unlike findings of a previous study2 that show the PCV in 500 Beagle puppies drops during their first month of life and then increases to a mean PCV of 41% by 3 months of age, results of the present study indicated that dogs ≥ 3 to ≤ 6 months of age still had a low mean PCV (37.6%) and cHct (37%). Those 3-month-old Beagles also had a mean MCHC of 35.3 g/dL,2 which aligned more with our findings for adult dogs (mean MCHC, 34.7 g/dL) than for juvenile dogs ≥ 3 to ≤ 6 months of age (mean MCHC, 34.0 g/dL). Infectious or parasitic comorbidities detected in some of the dogs in the present study could have contributed to our lower results. For instance, dogs with flea infestation or hook-worms can develop blood-loss anemia, and dogs with ehrlichiosis or anaplasmosis can develop nonregenerative anemia.10,11 Interestingly, even for dogs that had fleas or tested positive for E canis antibodies, we observed the same hematologic patterns, with lower results for PCV and cHct in juvenile versus adult dogs.
To improve the adoptability of shelter dogs, it is important to perform OHE or castration, even when limited history or diagnostic resources are available to determine presurgical health status.7 With early spay-neuter programs, the surgeries are performed on puppies as young as 6 to 14 weeks of age as well as on juvenile and adult dogs; thus, knowing clinically normal hematologic values for young dogs is beneficial.12 For veterinarians who routinely perform a PCV or CBC prior to a dog's surgery, the results of the present study should help improve interpretation of those hematologic results and clinical decision-making for determining whether animals are healthy enough for anesthesia and surgery. Specifically, only 2 dogs in the present study required postponement of their surgery; however, they both had results for PCV and cHct within reference limits, and all other dogs, including the remaining 25 dogs with infections or parasitism and dogs with results for PCV and cHct below reference limits, underwent OHE or castration with no related complications. Overall, this included 30 dogs with a cHct ≤ 35% and 28 dogs with a PCV ≤ 35%, of which 3 dogs had both a cHct and PCV ≤ 30%.
A previous study2 shows that the mean PCV was slightly lower for healthy female (41.9%) versus male (42.3%) 6-month-old Beagles but did not report the statistical analysis of these data. In a study13 of adult (1 to 9 years of age) sled dogs evaluated before and after a race, no differences in results were seen in any hematologic parameter for dogs grouped by sex.13 Similarly, our findings indicated no differences in results for PCV or cHct for male versus female dogs ≥ 3 months of age. However, in dogs < 3 months old, the mean cHct and reticulocyte count were higher for females (37.3% and 155,000 reticulocytes/µL) versus males (34.1% and 118,000 reticulocytes/μL). The reasoning for this was unclear because dogs with lower cHcts typically are expected to compensate with higher reticulocyte counts. Alternatively, the higher reticulocyte counts in these female dogs could have resulted in their higher cHct if the duration of increased RBC production had been longer in the female versus male dogs < 3 months old. Regardless, the mean cHct was significantly lower and the mean reticulocyte count was significantly higher for all juvenile dogs < 3 months old, compared with these parameters in adult dogs.
Because a PCV might be the only hematologic diagnostic test performed prior to elective surgeries in shelter dogs, we deemed the PCV and cHct important and reported results for both in the present study. A limitation was that the PCV measurements were performed by third-year veterinary students who were expected to have had less experience than technicians in a commercial laboratory. Although all students involved had previous training and hands-on practice on how to perform a PCV measurement, factors related to their measurements could have explained, in part, the discrepancy in results for PCVs versus cHcts for adult dogs of the present study. Some third-year veterinary students could have had extensive experience working in a veterinary clinic and performing tests including PCV, whereas others may have had less opportunity. Similarly, this varied practical experience with performing PCV measurements is likely true in veterinary practices and shelters. Although in adult dogs of the present study the discrepancy between the mean PCV (44.9%) and cHct (45.8%) was statistically significant, the difference was not considered clinically relevant, and this difference is within the total allowable error for cHct or PCV as determined by the American Society for Veterinary Clinical Pathology.14
Another limitation was that one hematologic analyzerc was used to assess samples from 123 dogs, whereas another analyzerg was used to assess samples from the remaining 15 dogs. This unplanned event occurred when the main analyzer was out of service for 1 week, during which time presurgical hemato-logic assessments for dogs awaiting surgery needed to be done in a timely fashion to make clinical decisions about whether to proceed with or postpone the surgeries. Both analyzers had been validated for use on blood samples from dogs and had quality control procedures performed regularly; thus, it was anticipated that the results from both analyzers were reliable and could be reported together.
Although 138 dogs overall were enrolled in the present study, the number of juvenile dogs (≤ 6 months of age) was relatively small, and few had parasitism or infection detected. Therefore, the study was limited in assessing the impact of these parasites and infectious diseases on the hematologic parameters of juvenile shelter dogs, which is an area that requires further study.
In conclusion, our findings indicated that the mean cHct and PCV were lower for juvenile (≤ 6 months of age) versus adult (> 6 months of age) shelter dogs, regardless of whether dogs with identified parasites or infectious diseases were included or excluded. Results also indicated that the mean MCHC was higher in adult dogs, whereas the mean reticulocyte count was higher in juvenile dogs. Sex was associated with hematologic results only among dogs < 3 months old, with the mean cHct and reticulocyte count lower for males versus females. Other than the 2 dogs that had their surgeries postponed because of infection (1 dog < 3 months of age with parvovirus infection and 1 dog > 6 months of age with anaplasmosis-related thrombocytopenia), the remaining 136 of the 138 (98.6%) shelter dogs presented for elective OHE or castration successfully underwent the surgeries as scheduled and then were returned to their shelters for adoption. Of these 136 dogs, 25 had evidence of parasitism or infection detected, and 50 of the 55 (90.9%) juvenile dogs that underwent surgery as scheduled had cHct below the lower limit of the RI. These findings supported our hypothesis that elective OHE or castration in juvenile shelter dogs would rarely need to be postponed because of results for PCV or cHct below the lower limits of RIs for adult dogs, even when comorbidities are considered.
Acknowledgments
This study was funded by the Kansas State University Department of Clinical Sciences, a private anonymous donor, and a Kansas State University Pet Tribute Grant.
The authors declare that there were no conflicts of interest related to this study.
The authors thank Mal Hoover for assistance with Figure 1.
Footnotes
Snap 4Dx, Idexx Laboratories Inc, Westbrook, Me.
Critocaps, Covidien, Minneapolis, Minn.
ADVIA 2120i, Siemens Medical Solutions, Malvern, Pa.
SNAP Parvo, Idexx Laboratories Inc, Westbrook, Me.
SigmaPlot, version 12.5, Systat Software Inc, San Jose, Calif.
Prism, version 7.03, GraphPad Software, San Diego, Calif.
HemaTrue, Heska Corp, Loveland, Colo.
Capstar, Elanco Animal Health, Greenfield, Ind.
Advantage Multi, Bayer, Shawnee Mission, Kan.
Trifexis, Elanco Animal Health, Greenfield, Ind.
Interceptor Plus, Elanco Animal Health, Greenfield, Ind.
Drontal Plus, Bayer Corp, Shawnee Mission, Kan.
Marquis, Merial Inc, Duluth, Ga.
Abbreviations
| cHct | Calculated Hct |
| MCHC | Mean cell hemoglobin concentration |
| MCV | Mean cell volume |
| OHE | Ovariohysterectomy |
| RI | Reference interval |
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