Reliability of using random urine samples for “spot” determination of fractional excretion of electrolytes in cats

Abstract

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.