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Today's Veterinary Practice May/June 2014 88 | Today's Technician tvpjournal.com accumulation. Microalbuminuria. Species-specific microalbuminuria assays can detect urine albumin concentrations as low as 1 mg/dL. Opinions vary on the use of these assays and their clinical implication, but some consider even small amounts of albumin in the urine as abnormal, possibly indicat- ing early or subclinical glomerular disease. Glucose Glucose is not normally present in the urine in quantities detectable on dipsticks. The test strip pad detects glucose by an enzymatic chemical reaction that results in a color change proportional to the amount of glucose present. While this reaction is specific for glucose, it is important to realize enzyme activity is limited, and outdated strips may give false–negative results. Temperature can also affect enzyme activity; refrigerated samples need to be at room temperature before testing. Glucose filtered through the glomeru- lus is normally reabsorbed in the proximal tubules. Glucosuria occurs with any con- dition that causes blood glucose levels to exceed the renal threshold for reabsorp- tion (renal threshold: dogs, 180–220 mg/ dL; cats, approximately 290 mg/dL). 1 • Diabetes mellitus is a common cause of glucosuria due to excessive blood glu- cose concentrations. • Stress in some animals (particularly cats) can cause marked transient hyper- glycemia; if hyperglycemia has sufficient magnitude, glucosuria results. • Renal tubular dysfunction is present when glucosuria is associated with nor- mal blood glucose concentrations; this dysfunction may be inherited (primary renal glucosuria, Fanconi syndrome) or associated with acquired renal tubular diseases. Ketones Ketones are normally produced at low lev- els that are undetectable in urine. They are formed during fat metabolism and include acetone, acetoacetic acid, and beta- hydroxybutyric acid. The glomerulus free- ly filters ketones, which are then excreted in the urine. The test strip pad detects excessive ketones in the urine by nitroprusside reac- tion. • This test is most sensitive to acetoacetic How to Prepare Urine for Microscopic Examination 1. Place 5 to 10 mL of urine in a clean centrifuge tube (this volume needs to be con- stant for every Ua or the number of cells, crystals, and casts will be influenced). 2. centrifuge urine at 1500 rpm for 5 minutes (Figure 3). sediment may be visible at the bottom of the tube when centrifugation is complete (Figure 4), and the amount of sediment corresponds to the amount of particulate matter (cells, crystals, etc) present in the urine. 3. Remove most of the super- natant, carefully avoiding disruption of the material at the bottom, leaving 2 to 3 drops of supernatant to remix with the sediment. 4. Gently tap or flick the tube with a finger to reconsti- tute the sediment with the remaining urine; avoid vig- orous mixing as this may cause cellular artifacts and disruption of casts. 5. Using a disposable drop- per, transfer one drop of reconstituted sediment to a clean microscope slide and place a coverslip over the sample (Figure 5). adding a urine sediment stain to the sample may improve nuclear detail and facilitate identification of cells. 2 stains, however, dilute the sample and affect semi- quantitative evaluation of the results. 1,3 stains may also add bacteria, fungal elements, and other debris to the sam- ple. examining both stained and unstained preparations is recommended. air-dried urine sediment stained with a Romanowski-type rapid stain, such as diff-Quik, can further facilitate the identifi- cation of cells and/or evalua- tion of cellular atypia. Figure 3. Standard centrifugation at 1500 rpm for 5 minutes Figure 4. Before (left) and after (right) centrifugation Figure 5. A cover slip is placed over a drop of urine on a clean microscope slide TVP_2014-0506_TT_Urinalysis-Part2.indd 88 5/25/2014 7:28:48 PM