Introduction

Myxomatous mitral valve disease (MMVD) is reported to be the most common canine heart disorder.¹ MMVD is characterized by a myriad of cellular changes including decreased valvular collagen content, disorganization of collagen fibrils, endothelial cell changes, and subendothelial thickening.^2–4 These cellular changes eventually progress to valvular deformation and failure of coaptation resulting in regurgitation of blood through the valve during systole. This progressive regurgitation can lead to cardiac remodeling and eventual ventricular dysfunction.⁵ Clinical presentations can vary in dogs, ranging from no symptoms for the duration of their lives to severe consequences including arrhythmias, pulmonary hypertension, and congestive heart failure (CHF).^6,7 Unfortunately, the factors influencing this progression in the individual canine are not fully understood. It is known however that both cardiac remodeling and CHF can induce inflammatory cytokines (TNF-α, IL-1, IL-6, IL-8, cortisol, catecholamines, and chemokines), resulting in a systemic inflammatory state.^8,9 This systemic inflammation has been demonstrated to have independent pathophysiological importance and is predictive of poor outcomes in humans with CHF.¹⁰ Currently, a variety of cardiac prognostic indicators are commonly used in veterinary medicine including plasma cardiac biomarkers (eg, N-terminal pro B-type natriuretic peptide or cardiac troponin-I) and various physical examination findings (eg, heart rate and murmur intensity).¹¹ While these prognostic indicators have proven useful for disease management, they do not utilize the underlying systemic inflammation seen with cardiac remodeling and CHF associated with MMVD.

Both the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) have been described in human medicine as an easily calculated prognostic value that uses commonly obtained hematologic peripheral blood neutrophil, platelet, and lymphocyte counts. The NLR has been previously identified as a predictor of mortality in a variety of human conditions, including cardiopathic diseases.^12–14 In particular, NLR was found to be a significant marker of decompensation as well as long-term mortality in humans with CHF.¹⁵ In humans, CHF has been found to have significant clinical effects on hemostasis including increased platelet activation, high plasma markers for thrombin activity, and fibrinolytic activity as well as being associated with an increased risk for thromboembolic disease.^16,17 Numerous studies of humans have demonstrated the prognostic value of PLR for various human diseases including multiple cancers, autoimmune diseases, and coronary artery disease.^18–20 Interestingly, PLR has not been demonstrated to be of significant prognostic value in humans with acute CHF.^21,22

In veterinary medicine, NLR has been shown to be a valuable prognostic indicator in dogs affected with a multitude of inflammatory diseases including various cancers, inflammatory bowel disease, and certain neurological disorders.^23–25 There are a limited number of studies assessing the role of PLR in veterinary medicine. A recent study demonstrated that PLR was significantly increased in dogs with chronic inflammatory enteropathy compared to healthy control dogs.²⁶ PLR has also been correlated with ICU length of stay for canine patients with severe hemorrhage. Additionally, it was found to be correlated with survival of patients with nonseptic disease processes.²⁷ To our knowledge, neither NLR nor PLR has been specifically investigated as a prognostic factor in dogs affected with CHF secondary to MMVD. The objective of this retrospective study was to evaluate the utility of NLR and PLR as a biomarker for the severity and short-term outcomes of MMVD dogs with CHF in comparison to presumptively preclinical MMVD dogs and healthy controls. The authors hypothesized that a higher NLR (but not PLR) in dogs with CHF secondary to MMVD would be associated with longer time in supplemental oxygen therapy, higher in-hospital furosemide dosages, and lower survival to hospital discharge.

Methods

The medical records database of a tertiary veterinary teaching hospital was searched for canine patients 2 years of age or older that were admitted to the hospital between March 2012 and March 2022. Cases were eligible for inclusion if there was a diagnosis of CHF secondary to MMVD resulting in hospitalization (including diuretic therapy and oxygen supplementation). Individual dogs were only included once in this study (from their initial CHF episode if records were available). Dogs were not excluded on the basis of a previous diagnosis of CHF (ie, relapse back into CHF). The criteria for CHF were MMVD identified by echocardiographic or postmortem evaluation and concurrent pulmonary edema as diagnosed by thoracic radiographs that were interpreted by a board-certified radiologist. The criteria for presumptive preclinical MMVD dogs included mitral valve disease identified by echocardiographic evaluation or high clinical suspicion based on murmur classification (left apical systolic heart murmur) in a typical breed (small- or toy-breed dogs). The criteria for healthy control patients included no signs of cardiac disease reported on physical examination (such as heart murmurs or arrhythmias) as well as review of any diagnostic imaging results if available. MMVD CHF patients were divided into tertile age range groups (ie, 3 to 7, 8 to 12, and 13 to 16 years of age). Controls and presumptive preclinical MMVD dogs were age-matched at a ratio of 1:1 to the 3 age range groups of affected dogs in an attempt to have comparator populations more accurately represent the primary study group (that is, CHF MMVD dogs). Dogs were also age matched to account for potential age-related influence on lymphocyte populations.²⁸ Patients were excluded if a CBC was not performed within 24 hours of admission; any potential drug interactions that could affect CBC parameters (ie, glucocorticoids, phenobarbital, or immunomodulating therapies) were identified; the patient was diagnosed with a concurrent disease process that primarily affects neutrophils, platelets, or circulating lymphocytes (ie, Cushing disease, infections, or immune-mediated thrombocytopenia); or the patient was of the Cavalier King Charles Spaniel (CKCS) or Greyhound breeds.^29,30 Concurrent disease processes were screened using review of history and physical examination findings for signs concerning for systemic disease, review of hematologic and biochemical analysis, ancillary laboratory testing (when available), and any diagnostic imaging results. Medical records were reviewed, and the following clinical factors were recorded: signalment; physical examination findings from initial presentation to the hospital (including murmur grade/classification, body temperature, heart rate, respiratory rate, and SpO² measurements); medical treatments instituted (ie, diuretics and time in oxygen therapy); in CHF patients, the American College of Veterinary Internal Medicine (ACVIM) MMVD stage; length of hospitalization; ultimate outcome (survival to discharge or euthanasia/natural death during hospitalization); and confirmation of subsequent hospital re-presentation due to CHF (ie, yes or no, patients re-presented to the hospital for subsequent CHF episodes).³¹ Hematologic analyses were performed routinely by an in-house automated CBC analyzer (ADVIA 2120i; Siemens Healthcare GmbH) using whole blood in EDTA anticoagulant. All automated analyzer findings, including WBC differential counts, were verified by a trained clinical pathology technician on a Wright-Giemsa–stained blood smear. Any results in question (ie, anemia or thrombocytopenia) were sent for additional review by a board-certified clinical pathologist. The cell counts used were from the in-house automated analyzer unless the results differed from that of a manual count. NLR was calculated by dividing the total neutrophil count (immature and mature types) by the total lymphocyte count, and the PLR was calculated by dividing the total platelet count by the total lymphocyte count.

Distribution of continuous variables was evaluated visually and by the Skewness and Kurtosis tests for normality, and most continuous variables were not normally distributed. Therefore, results are reported as median (range) and nonparametric tests were used for analysis. The Mann-Whitney test was used to examine the association of continuous variables with 2-level categorical variables, while the Spearman correlation was employed to investigate correlations between continuous variables. The Fisher exact test was used to examine the association between categorical variables because some cells had ≤ 5 observations. The Liu method was used to calculate an empirical optimal cut point, the corresponding area under the receiver operating curve (AUC) at that cut point, and the sensitivity and specificity at that cut point.³² For these calculations, outcome was defined as discharged from the hospital (0) or euthanized (1), as no patients experienced natural death, and AUCs were calculated for NLR and absolute neutrophil count. The AUC was also calculated as the average (95% CI) receiver operating curve value, averaged over the (0,1) false-positive rate domain. A P value < .05 was considered significant for all tests. All statistical evaluations were performed using a statistical software package (Stata version 14.0 for Mac; Stata Corp).

Results

Forty-seven dogs hospitalized because of CHF secondary to MMVD were included in the study. Twenty-eight (59.6%) dogs were male (24 neutered [51.1%]), and 19 (40.4%) dogs were female (17 spayed [36.2%]). Breeds represented included mixed breed (n = 17 [36.2%]), Chihuahua (4 [8.5%]), Dachshund (3 [6.4%]), Pomeranian (3 [6.4%]), Yorkshire Terrier (2 [4.3%]), Lhasa Apso (2 [4.3%]), Doberman Pinscher (2 [4.3%]), and 1 (2.1%) each of the following: Shih Tzu, Maltese, Bichon Frise, Coton de Tulear, Havanese, Great Dane, Miniature Schnauzer, Shar-Pei, English Bulldog, Miniature Pinscher, Jack Russell Terrier, Beagle, Golden Doodle, and Chinese Crested. A total of 46 dogs were classified as ACVIM MMVD Stage C, with only 1 dog being classified as ACVIM MMVD Stage D. The median age was 11 years (range, 3 to 16 years). The median heart rate of the CHF group was 150 beats/min (bpm; range, 100 to 225 bpm). The median NLR of the CHF group was 6.41 (range, 2.56 to 22.80). The median PLR was 223.35 (range, 75.52 to 1,041.94). Median measured SpO² during presentation was 94.5% (range, 81% to 100%). The median time on supplemental oxygen therapy was 24 hours (range, 5 to 120 hours). The median cumulative dose of IV furosemide administration was 2 mg/kg (range, 1 to 8 mg/kg).

Forty-seven age-matched presumptive preclinical MMVD dogs were retrospectively included in the study. Twenty-five (53.2%) dogs were male (24 neutered [51.1%]), and 22 (46.8%) dogs were female (21 spayed [44.7%]). Breeds represented included mixed breed (n = 12 [25.5%]), Dachshund (6 [12.8%]), Toy Poodle (4 [8.5%]), Yorkshire Terrier (3 [6.4%]), Shih Tzu (2 [4.3%]), Jack Russell Terrier (2 [4.3%]), Havanese (2 [4.3%]), Boston Terrier (2 [4.3%]), and 1 (2.1%) each of the following: Chihuahua, Bichon Frise, Lhasa Apso, Golden Doodle, Whippet, Papillon, Labrador Retriever, West Highland White Terrier, Shetland Sheepdog, Cocker Spaniel, Bull Terrier, Brittany Spaniel, German Shorthaired Pointer, and Vizsla. A total of 42 dogs had confirmatory diagnosis of MMVD based on echocardiographic imaging, while 5 dogs were included on the basis of presumptive physical examination findings (ie, left apical systolic heart murmur in a typical breed). The median age was 11 years (range, 7 to 15 years). The median heart rate was 120 bpm (range, 72 to 180 bpm). The median NLR of the dogs with murmurs was 4.66 (range, 1.93 to 31.0). The median PLR was 242.53 (range, 74.58 to 1,422.50).

Forty-seven age-matched healthy control dogs were retrospectively included in the study. Thirty-three (70.2%) dogs were male (29 neutered [61.7%]), and 14 (29.8%) dogs were female (14 spayed [29.8%]). Breeds represented included mixed breed (n = 15 [31.9%]), Labrador Retriever (4 [8.5%]), German Shepherd Dog (4 [8.5%]), Yorkshire Terrier (2 [4.3%]), Beagle (2 [4.3%]), Boston Terrier (2 [4.3%]), Golden Retriever (2 [4.3%]), Border Collie (2 [4.3%]), English Springer Spaniel (2 [4.3%]), Siberian Husky (2 [4.3%]), and 1 (2.1%) each of the following: Shih Tzu, Dachshund, Bichon Frise, Great Dane, Miniature Pinscher, West Highland White Terrier, Vizsla, Australian Shepherd, Akita, and Pug. The median age was 10 years (range, 3 to 14 years). The median heart rate of healthy controls was 128 bpm (range, 40 to 225 bpm). The median NLR of the healthy control group was 3.95 (range, 1.50 to 12.07). The median PLR was 191.43 (range, 45.56 to 720.73).

There was a statistically significant difference in the NLR between groups (CHF dogs to presumptive preclinical MMVD dogs, P < .001; CHF dogs to healthy controls, P < .001; Figure 1), but there was no significant difference when comparing PLR between groups (CHF dogs to presumptive preclinical MMVD dogs, P = .56; CHF dogs to healthy controls, P = .23; Figure 2). Neither NLR nor PLR was associated with murmur grade or heart rate among CHF dogs (NLR P = .72, PLR P = .47; NLR P = .3, and PLR P = .06, respectively). Among the CHF dogs, both NLR and PLR were significantly associated with increasing cumulative dosages of furosemide (ρ = 0.3, P = .04; and ρ = 0.4, P = .02, respectively). There was a moderate positive association between NLR and duration of supplemental oxygen therapy within the CHF group as well (ρ = 0.4; P = .01). Conversely, there was no association identified between PLR and the duration of oxygen therapy (P = .27). No associations were identified between NLR or PLR and either ultimate outcome, that is survival to discharge versus euthanasia/natural death during hospitalization (NLR P = .08; PLR P = .46), or whether a patient re-presented to the hospital for subsequent CHF episodes (NLR P = .32; PLR P = .59).

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Box-and-whisker plot comparing neutrophil-to-lymphocyte ratios for congestive heart failure (CHF) dogs, presumptive preclinical (PPC) dogs, and healthy control dogs (n = 47 each). The central horizontal lines indicate median value. The upper and lower lines of the plot represent upper and lower quartiles of the values, respectively. The circles represent outliers. There is a significant difference between the noted groups (CHF dogs to PPC dogs, *P < .001; CHF dogs to healthy control dogs, ⁑P < .001).

Citation: Journal of the American Veterinary Medical Association 261, 11; 10.2460/javma.23.03.0131

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Box-and-whisker plot comparing platelet-to-lymphocyte ratios for CHF dogs, PPC dogs, and healthy control dogs (n = 47 each). The central horizontal lines indicate median value. The upper and lower lines of the plot represent upper and lower quartiles of the values, respectively. The circles represent outliers. There is no significant difference between the noted groups (CHF dogs to PPC dogs, P = .56; CHF dogs to healthy control dogs, P = .23).

Citation: Journal of the American Veterinary Medical Association 261, 11; 10.2460/javma.23.03.0131

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For NLR and outcome, the empirical optimal cut point was 8.2, the AUC was 0.91, and the sensitivity and specificity were 100% and 81%, respectively, at that point. For absolute neutrophil count and outcome, the empirical optimal cut point was 9.2 X 10⁹/L, the AUC was 0.89, and the sensitivity and specificity were 100% and 78%, respectively, at that point. The mean AUC for NLR and outcome and absolute neutrophil count and outcome were 0.9 (95% CI, 0.8 to 1) and 0.8 (95% CI, 0.7 to 0.9), respectively. The results of CBC parameters and calculated NLR/PLR values for each group are summarized (Table 1).

Discussion

This study investigated dogs with acute CHF secondary to MMVD to assess whether NLR or PLR could be used as a marker of disease severity or be of prognostic value. It was hypothesized that a higher NLR (but not PLR) in dogs with CHF secondary to MMVD would be associated with poorer short-term outcomes and increased mortality in hospital (ie, lower survival to hospital discharge). Several veterinary publications have discussed the association of both NLR and PLR with various diseases including inflammatory and neoplastic processes.^23,24,33 The results of the current study confirmed that NLR (but not PLR) is increased in dogs with CHF secondary to MMVD compared to both presumptive preclinical MMVD dogs and healthy controls. Correction for multiple testing was not performed because in early exploratory studies such as this one, the benefit of initial discoveries that can pave the way for future studies outweighs the risk of a type I statistical error in which a false-positive finding is reported.³⁴ These findings are in alignment with previous studies of humans that demonstrate similar differences.^15,21,22 Increased production of neutrophils is commonly seen in inflammatory states. Neutrophils play a diverse but key role in the immune system’s response to inflammatory conditions such as producing cytokines, modulating the activities of neighboring cells, and regulating macrophages for long-term immune responses.³⁵ By these mechanisms, a proinflammatory disease such as CHF could result in alterations to circulating neutrophil counts. Additionally, there are a variety of proposed mechanisms by which lymphocytopenia is observed in human patients with heart failure including lymphocyte apoptosis, downregulation of the proliferation of lymphocytes, and neurohumoral activation.^36,37 Changes in both cell lines are likely to influence NLR in canine patients with CHF. Previous studies have investigated the WBC differentials in canine cardiac patients. The results of this study are in alignment with these previous studies (Table 1). In 1 study³⁸ of canine patients with CHF secondary to a variety of cardiac diseases (including MMVD), there was significantly elevated median total WBC counts when compared to nonclinical cardiac disease dogs and healthy controls (14.0 X 10⁹/L vs 8.4 X 10⁹/L and 9.0 X 10⁹/L, respectively). An additional study³⁹ comparing WBC differentials in CHF dogs (including MMVD and dilated cardiomyopathy patients) also found similar trends in total WBC, neutrophil, and lymphocyte counts (11.96 X 10⁹/L, 8.9 X 10⁹/L, and 1.5 X 10⁹/L, respectively), particularly when compared to the results of this study.

As demonstrated (Table 1), the primary driving factor for elevated NLR in the CHF dogs when compared to either control groups appears to be the absolute neutrophil count. This is confirmed by the statistically significant difference in median absolute neutrophil count between CHF dogs and both presumptive preclinical and healthy control dogs. In contrast, there is a large degree of overlap in total lymphocyte count that shows no significant difference between groups. While analysis of AUC demonstrates that the specificity of NLR is higher (albeit slightly) than absolute neutrophil count (81% and 78%, respectively) regarding patient short-term outcome when using the optimal cut points identified above, the overlap in the 95% CIs of the mean AUC for NLR and absolute neutrophil count to short-term outcomes (ie, survival to discharge), respectively, indicate that these receiver operating curves are not statistically different from one another. It is also important to note that NLRs above 8.2 and absolute neutrophil counts > 9.2 X 10⁹/L would have higher true positives and false-positive rates. Interestingly, the AUC analysis demonstrates a relatively high predictive power of both NLR and absolute neutrophil count regarding short-term outcomes (AUC approx 0.9), which is in contrast to the lack of association previously identified between NLR and short-term outcomes in this study. This may be influenced by a relatively small sample size, as there was a near-significant association between NLR and short-term outcomes (P = .08). Future prospective studies, particularly those with larger sample sizes, are needed to better investigate the clinical implications of these findings and determine which of these 2 values may prove to be the better marker for outcomes in dogs with CHF secondary to MMVD.

In contrast to NLR, no association was identified between PLR and dogs with CHF secondary to MMVD. One potential explanation for this could be the longer life-span of platelets (5 to 7 days in the dog), particularly when compared to the life-span of circulating neutrophils.⁴⁰ Fluctuations in circulating platelet levels due to inflammation may not be readily apparent in the acute presentation that is typically seen in patients with CHF. In contrast, platelet life-span has been shown to be shortened in canine patients with experimentally induced mitral regurgitation (postulated to be due to shear stress from the regurgitation).⁴⁰ This finding does not appear to have a significant impact on circulating platelet levels in dogs in this study, although the significance of this finding is not well studied in dogs with naturally occurring MMVD. While heart failure in humans is associated with increased thromboembolic stroke risk, the clinical impact of a procoagulant state has not been previously identified in dogs.⁴¹ The findings reported in this study are in alignment with this, regarding no clinically significant changes to PLR being identified.

NLR was found to be associated with both higher cumulative dosages of diuretics as well as duration of supplemental oxygen therapy. A similar association was identified between PLR and dosages of diuretics as well. In human patients with CHF, higher NLR values had an increased incidence of radiographic signs of heart failure (such as cardiomegaly or interstitial edema).¹⁵ Patients with worse CHF (ie, radiographically apparent interstitial edema that requires higher cumulative diuretic dosages for stabilization) may represent a more severe proinflammatory state by which changes to NLR and PLR are more frequently seen. Standard management of CHF in both humans and dogs includes diuretic therapy and oxygen supplementation as needed.^31,42 In human patients with advanced heart disease, there has been a negative association between a higher dose of loop diuretics and survival.^43,44 The increased diuretic dose and time on oxygen supplementation in this study may represent worse disease severity and decompensation for which NLR (and to a lesser extent PLR) may serve as a readily available marker. While there was a statistical difference, our data demonstrated mixed results regarding short-term clinically significant difference in outcome (that is, survival to discharge vs euthanasia/natural death in hospital) or re-presentation rates (ie, yes or no, patients re-presented to the hospital for subsequent CHF episodes) with AUC analysis (AUC approx 0.9), suggesting high predictive power of outcomes compared to there being no significant association identified between NLR and short-term outcomes (P = .08). This contrasts with human studies in which elevated NLR was consistently a predictor for in-hospital and postdischarge 3-year mortality in acute heart failure patients.⁴⁵ It is possible that hospitalization and stabilization were not pursued in sicker patients that were euthanized, which could influence the results of this study, particularly when comparing to human patients. The observed difference in NLR between dogs with CHF and presumptive preclinical MMVD dogs highlights the potential utility of this value as a marker for disease severity. Further studies are necessary to investigate the usefulness of NLR for identifying MMVD dogs at a greater risk of developing CHF.

The range of NLR values in healthy humans has been previously evaluated and demonstrated to be approximately 1.0 to 2.0; values 2.0 to 3.0 represent a gray zone, which may represent subclinical inflammation/stress.^46,47 Interestingly, the median NLR values of all groups in this study (including the healthy controls) were higher than previously reported human values (CHF group, 6.41; presumptive preclinical MMVD dogs, 4.66; healthy controls, 3.95). Other veterinary studies have also found the NLR values of healthy control dogs to be greater than the human range referenced above.^24,33 The added stress of hospitalization could result in alterations to the CBC parameters independent of the presence of CHF, although all groups demonstrated an elevation above the reported human values. This may represent a greater influence of sympathetic tone causing a stress leukogram in canine patients (even those that are healthy or seen on an outpatient basis).⁴⁸ These differences also highlight the need for further studies evaluating the normal NLR range in healthy canine patients.

In comparison to previously established markers of disease severity (such as murmur grade or heart rate), there was no association identified with NLR or PLR.¹² One potential explanation for this lack of association could be related to the subjective nature of these measurements, particularly in regard to murmur grading. Previous studies have shown varying degrees of interobserver agreement in diagnosing mitral valve murmurs ranging from 63% to 88%.⁴⁹ Influencing factors included the clinician’s experience level or the degree of physical exertion prior to auscultation. It is not unreasonable to extrapolate these findings to the auscultation of a patient in respiratory distress in an emergency setting. Additionally, due to the retrospective nature of this study, clinician experience levels were not consistent and ranged from newly graduated veterinarians to board-certified specialists. These findings, combined with the previously noted associations, demonstrate the need for future controlled studies to better compare NLR and PLR to previously established markers of disease severity.

There were limitations of this study that should be recognized. This was a retrospective study in dogs presenting to a tertiary hospital. The number of dogs evaluated during this time period therefore may only represent a small portion of the overall population and may have been influenced by referral biases and owners’ finances. The assessment and treatment of patients was not standardized. This includes the potential for administration of cardiac medications prior to venipuncture for the CBC, which could have impacted some of the hematologic results, particularly if the patients’ congestive status was in transition. Additionally, medical record data were missing for some dogs and long-term follow-up information was not obtained. This is particularly relevant for the median cumulative dose being lower than one might typically expect for a patient hospitalized for CHF (median, 2 mg/kg; range, 1 to 8 mg/kg), and this limitation should be taken into consideration when assessing this value. Second, breed exclusions were necessary due to factors that could have influenced the assessed variables, specifically the exclusion of the CKCS breed. It has been previously well established that the CKCS breed often has idiopathic asymptomatic thrombocytopenia, which is suspected to be an inherited trait.³¹ The CKCS breed has also been shown to have a higher incidence and earlier onset of MMVD and thus potentially greater cardiac morbidity and mortality.⁵⁰ Thus, exclusion of this breed may have inadvertently influenced the results of this study. The lack of definitive diagnosis (ie, echocardiogram) for our presumptive preclinical MMVD group could have resulted in patients with other etiologies (aside from MMVD), causing a left apical systolic heart murmur to be included in this study and biasing the results. Additionally, as discussed previously, euthanasia of sicker patients could have influenced the outcome results of this study.

Finally, this study required a CBC to be performed within 24 hours of hospital admission. Patients with milder episodes of CHF may not necessarily require hospitalization or receive a full systemic workup (including a CBC).⁴⁰ This may bias the results toward sicker patients. Regardless, the data presented in this study have provided some understanding of the systemic inflammatory changes seen in CHF secondary to MMVD. Future work should include longitudinal studies to provide additional insight into the long-term prognostic value of both NLR and PLR. Potential areas of investigation include specific analysis regarding different stages of MMVD or other forms of cardiac disease (such as dilated cardiomyopathy). Additionally, further analysis of NLR and PLR for correlation with other markers of cardiac disease (such as pro-BNP or troponin-I) or disease severity scores (like APPLE scores) may be worthwhile. In summary, the results of this study suggest that NLR (but not PLR) is elevated in dogs suffering from acute CHF secondary to MMVD compared to both presumptive preclinical MMVD dogs and healthy controls. While a positive association was identified between NLR and markers of disease severity (higher cumulative diuretic dosages and time on oxygen supplementation), there was no impact on ultimate short-term outcome or re-presentation rates to the hospital. Future studies are needed to better investigate the long-term utility of both NLR and PLR in canine patients suffering from CHF secondary to MMVD.