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Summary

Two methods for evaluating glomerular filtration rate (gfr), after single iv administration of inulin, were assessed in dogs after partial nephrectomy. The first method, determination of plasma clearance of inulin (PCIn), was taken as the quotient of the administered dose of inulin (1,000 mg) divided by the area under the plasma inulin concentration vs time curve. The second estimate of renal function was obtained from the plasma concentration of inulin 75 minutes after iv administration of 1,000 mg: C(75). The values for PCIn and C(75) were related (R 2 = 0.955, P < 0.0001 and R 2 = 0.867, P < 0.0001, respectively) to a previously validated method for measurement of GFR in dogs, urinary clearance of exogenous creatinine (CCr). Results of this study support use of PCIn and C(75) values to estimate GFR in dogs with reduced renal function. In particular, PCIn and C(75) were closely related to CCr in partially nephrectomized dogs with plasma creatinine concentration within the reference range for clinically normal dogs.

Free access
in American Journal of Veterinary Research

Summary

A relation exists between colloid osmotic pressure (π) and serum total protein concentration; equations describing this relation have been used to determine a calculated value for π. However, the relation between total protein concentration and π is altered by the method used to measure protein and by changes in the ratio of concentrations of albumin (A) to globulin (G). We developed nomograms for estimating π from A and G concentrations, using samples obtained from clinically normal animals and compared the accuracy of these nomograms with that of previously described equations relating π to total protein concentration. For comparison, serum samples from canine (n = 106), equine (n = 79), feline (n = 24), and bovine (n = 27) patients admitted to the University of Georgia Veterinary Medical Teaching Hospital were used. Results indicated that nomograms based on protein concentration estimated by a refractometer generally were the least reliable. Although predictive nomograms, using total protein concentration determined by the biuret method, provided better results for serum samples, there was considerable variation between measured and calculated values for π in all species studied. Calculated values for π derived from A and G concentrations were most closely related to measured values for π dogs, horses, and cats. However, calculated values for π differed from measured values by as much as 5 mm of Hg for some samples by each of the methods of estimation. These results indicate that, although calculated values for π may be most accurate when variations in the A-to-G ratio are accounted for in the nomogram, none of the calculation methods provided a consistently accurate estimate of π. For clinical patients, π based on these nomograms cannot replace direct measurement.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate utility of a method for estimating glomerular filtration rate after a single IV injection of inulin.

Animals

Cats that were renal intact (n = 3) or had renal mass reduced by partial nephrectomy (n = 6).

Procedure

Plasma clearance of inulin (PCIn) was taken as the quotient of the administered dose of inulin (150 mg) divided by the area under the plasma inulin concentration versus time curve determined by 3 methods (PCIn1 – PCIn3). Results for PCIn were compared with simultaneously obtained values for urinary clearance of exogenous creatinine (CCr), an accepted method for the estimation of glomerular filtration rate (GFR) in cats.

Results

Values for PCIn were closely related (R 2 ranged from 0.951 to 0.972, P < 0.0001 in all instances) to CCr. However, PCIn3 provided an estimate of GFR that consistently overestimated CCr.

Conclusion

Determination of PCIn by use of PCIn1 and PCIn2 provided a reliable estimate of GFR in cats of this study.

Clinical Relevance

Determination of PCIn appears to provide a reliable estimate of GFR in cats with early-stage renal disease and no evidence of derangement of body fluid status. In particular, PCIn2, which requires only 3 determinations of plasma inulin concentration, should be considered when an estimate of GFR is sought in a cat with suspected early-stage renal disease. (Am J Vet Res 1996;57:1702–1705)

Free access
in American Journal of Veterinary Research

Summary

Clinically normal dogs were evaluated in states of dehydration, euhydration, and after fluid administration to determine effects of hydration state on renal clearance values. Endogenous creatinine, exogenous creatinine, and [14C]inulin clearances, were determined to measure glomerular filtration rate (gfr); in some experiments p-aminohippurate clearance was determined to measure renal plasma flow.

Dehydration caused significant (P < 0.05) decrease in clearance values, compared with euhydration, and clearance values during euhydration were significantly (P < 0.05) less than values obtained after a single gavage with water (30 ml/kg of body weight).

Sustained administration of 3 fluid regimens was evaluated for effects on clearance values (treatment A = 30 ml of lactated Ringer’s solution/kg/h; treatment B = 30 ml of water/kg by gavage hourly; treatment C = 10 ml of glucose:lactated Ringer’s solution/kg/h). All regimens of fluid therapy caused significant P < 0.05), progressive increases in gfr, but treatment C resulted in the most stable gfr values. Increases in clearance values were associated with positive fluid balance; the rate of fluid administration was greater than the rate of urine formation.

Data from 285 gfr determinations on 85 dogs were evaluated retrospectively. For each determination, three 20-minute urine collections were made beginning 40 minutes after 30 ml of water/kg was given by gavage. Values between collections were significantly (P < 0.05) different, but varied by < 3%.

Comparison of methods for measurement of gfr indicated that endogenous creatinine clearance and [14C]inulin clearance were highly correlated (R 2 = 0.82), but mean clearance values were markedly different (mean ± sem, 28.70 ± 0.01 and 37.07 ± 1.29 ml/min, respectively).

Exogenous creatinine clearance and [14C]inulin clearance were highly correlated (R 2 = 0.95), and mean values were 40.54 ± 0.70 and 41.02 ± 0.70 ml/min respectively.

We conclude that: state of hydration has a marked effect on gfr; rate of fluid administration that exceeds rate of urine production results in progressive increases in gfr; a single water gavage of 30 ml/kg gives stable gfr values for three 20-minute collection periods, may avoid subclinical states of dehydration, and facilitates accurate urine collections; and endogenous creatinine clearance, as conducted in this study, does not accurately measure gfr.

Free access
in American Journal of Veterinary Research

SUMMARY

Objective

To determine whether the “spot” method of determining fractional excretion (FE) of electrolytes in cats is accurate.

Animals

5 clinically normal young adult female cats.

Procedure

Cats were acclimated to metabolism cages, and 2 consecutive 72-hour collections of urine were made to determine FE of total calcium, potassium, total magnesium, sodium, and phosphorus by conventional methods, using endogenous creatinine clearance as an estimate of glomerular filtration rate. During collections, small samples of urine were obtained by cystocentesis at 8 am, 3 pm, and 9 pm for determination of FE of the electrolytes by use of the “spot” method.

Results

Values from “spot” determinations were highly variable, compared with 72-hour values, with a high percentage falling outside the range of mean ± 2 SD for 72-hour FE values.

Conclusions and Clinical Relevance

The “spot” method for determining FE is not precise, and if used, caution and judgement should be exercised in interpretation of the results. (Am J Vet Res 1997;58:1184–1187)

Free access
in American Journal of Veterinary Research

Summary

Thirty-one clinically normal Cocker Spaniels, Miniature Schnauzers, and Doberman Pinschers (28 female, 3 male) 7 to 8 years old were uninephrectomized (month −2) to increase the risk of renal damage associated with reduction of renal mass. Two diets, differing principally in protein concentration, were used to test the hypothesis that high dietary protein intake causes renal damage in aging dogs.

For 2 months after uninephrectomy, all dogs were fed diet A (18% protein). After glomerular filtration rate (gfr) was measured (month 0), 16 dogs were assigned to group A and were fed diet A for an additional 48 months. The other 15 dogs were assigned to group B, and were fed diet B (34% protein) for the subsequent 48 months. At 6-month intervals, GFR and urine protein-to-creatinine ratio (UP/C) were determined. At 48 months, terminal studies were done, survivors were euthanatized, and tissues were examined.

Of 16 dogs in group A, 10 survived, compared with 13 of 15 in group B. Among survivors, a significant difference in GFR was not found between groups A and B, and decrease in GFR was not evident with time in either group. At 48 months, oral administration of casein caused minor acute effects on GFR and renal plasma flow in dogs of groups A and B.

The UP/C values increased significantly (P = 0.001) from baseline values, but the increase was not progressive. The UP/C values were not affected by diet. Some dogs in both groups developed UP/C > 1.0.

Morphologic studies performed on kidneys removed at -2 months (nephrectomy) and at 48 months (necropsy) revealed increased kidney weight in both groups at month 48, compared with month −2 (P = 0.003); at month 48, kidney weight change was significantly (P = 0.004) greater in group-B than in group-A dogs. Increased glomerular area at month 48, compared with month −2, was significantly (P = 0.000) related to time, but not to diet.

Significant (P = 0.000) increase in glomerular mesangial matrix, interstitial fibrosis (P = 0.001), cell infiltration (P = 0.000), and lesions of the renal pelvis (P = 0.04) was observed between month −2 and month 48. Time, representing combined effects of uninephrectomy and aging, was the major factor responsible for the morphologic changes. Diet effects were significance (P = 0.008) for cell infiltration, but did not reach significance for mesangial matrix accumulation, fibrosis, or pelvic lesions. Kidney mineral analysis revealed no renal mineralization in either group between −2 and 48 months.

Results indicated that GFR did not decrease with time during the geriatric peroid studied, but severity of renal lesions was increased. Effects of time and uninephrectomy, although not separable, were more important than those of dietary protein intake on progression of renal lesions.

Free access
in American Journal of Veterinary Research