Reliability of using reagent test strips to estimate blood urea nitrogen concentration in dogs and cats

Objective-To evaluate the clinical accuracy of reagent test strips used to estimate BUN concentration in dogs and cats. Design-Prospective study. Animals-116 dogs and 58 cats. Procedure-Blood samples were collected at the time of admission to the hospital. Estimates of BUN concentration obtained with reagent test strips (category 1 [5 to 15 mg/dL], 2 [15 to 26 mg/dL], 3 [30 to 40 mg/dL], or 4 [50 to 80 mg/dL] were compared with SUN concentrations measured with an automated analyzer. For dogs, category 1 and 2 test strip results were considered a negative result (nonazotemic) and category 3 and 4 test strip results were considered a positive result (azotemic). For cats, category 1, 2, and 3 test strip results were considered a negative result (nonazotemic) and category 4 test strip results were considered a positive result (azotemic). Results-On the basis of SUN concentration, 40 of the 174 (23%) animals (20 dogs and 20 cats) were classified as azotemic. One dog and 2 cats had false-negative test strip results, and 1 dog had a false-positive result. Sensitivity and specificity were 95% (20/21) and 99% (94/95), respectively, for dogs and 87% (13/15) and 100% (43/43), respectively, for cats. Conclusions and Clinical Relevance-Results suggest that reagent test strips are a reliable method for rapidly estimating BUN concentrations in dogs and cats. Because test strip results are only semiquantitative and there remains a potential for misclassification, especially in cats, urea nitrogen concentration should ultimately be verified by means of standard chemistry techniques.