Chapter 187 The dipstick colorimetric test is the most common screening test for proteinuria. This test is inexpensive, easy to use, and primarily measures albumin. However, sensitivity and specificity for albuminuria are relatively low with this method. False-negative results (decreased sensitivity) may occur with Bence Jones proteinuria, low urine concentrations of albumin, or dilute or acidic urine. The lower limit of detection for the conventional dipstick test is approximately 30 mg/dl. False-positive results also are common in both cats and dogs with dipstick testing but occur more frequently in cats. For example, when 599 canine and 347 feline urine samples were analyzed by both a conventional urine protein test strip method (Multistix Reagent Strips or Roche Chemstrip 9) and a canine or feline albumin-specific quantitative enzyme-linked immunosorbent assay (ELISA) (see later) there were disparate results. The sensitivity of conventional urine protein dipsticks for albuminuria in canine and feline urine (a trace positive reaction or greater) was 81% and 90%, respectively, but the specificity was only 48% and 11%, respectively (Lyon et al, 2010). The sulfosalicylic acid (SSA) precipitation test is performed by mixing equal quantities of urine supernatant and 3% to 5% SSA in a glass test tube and grading the turbidity resulting from precipitation of protein on a 0 to 4+ scale. In addition to albumin, the SSA test can detect globulins and Bence Jones proteins to a greater extent than the dipstick test. False-positive results may occur if the urine contains radiographic contrast agents, penicillin, cephalosporins, sulfisoxazole, or thymol (a urine preservative), and for unknown reasons. The protein content also may be overestimated with the SSA test if uncentrifuged, turbid urine is analyzed. The reported sensitivity of the SSA test is approximately 5 mg/dl. Because of the relatively poor specificity of conventional dipstick analysis, many reference laboratories confirm a positive dipstick test result for proteinuria using the SSA test. The sensitivity of the SSA test for albuminuria in canine and feline urine (a trace positive reaction or greater) was found to be 73% and 58%, respectively, but the specificity was only 64% and 25%, respectively (Lyon et al, 2010). For feline urine samples, both routine screening tests (dipstick and SSA) performed poorly and appear to be of minimal diagnostic value because of an unacceptably high number of false-positive results. For both dipstick and SSA tests, the positive and negative likelihood ratios were close to 1 and the positive and negative predictive values were close to 50%, which indicates that neither test provided useful information regarding albuminuria. Based on these data, urine albumin detection in the feline patient always should be performed with a higher-quality assay such as the species-specific ELISA. In cats with chronic kidney disease, the accuracy of the dipstick and SSA tests improves in comparison with the feline-specific albuminuria assay (Hanzlicek et al, 2012), presumably due to a higher magnitude or a higher percentage of albumin in the urine. The use of microalbuminuria tests is indicated in the following circumstances: 1. When conventional screening tests for proteinuria produce equivocal or conflicting results or false-positive results are suspected. 2. When conventional screening tests for proteinuria give negative results in apparently healthy older dogs and cats and a more sensitive screening test is desired. 3. When conventional screening tests for proteinuria give negative results in apparently healthy young dogs and cats with a familial risk for developing proteinuric renal disease and a more sensitive screening test is desired. 4. When conventional screening tests for proteinuria give negative results in dogs and cats with chronic illnesses that are associated with proteinuric renal disease and a more sensitive screening test is desired. 5. Follow-up after a positive result on a previous microalbuminuria test to document persistence of the albuminuria.
Proteinuria/Albuminuria
Implications for Management
Detection of Proteinuria
Detection of Albuminuria
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
