Urinalysis is performed to obtain information from urine samples.
There are various aspects to urinalysis:
Urine specific gravity
Urine specific gravity should be measured using a refractometer. Urine SG can also be determined by using a urine dipstick but this is unreliable and is not recommended.
The prism cover of the refractometer should be opened and the calibration of the refractometer checked using distilled water. With the distilled water the result should read 1.000. If it is different to this the refractometer can be recalibrated using the recalibration screw. The refractometer prism should be dried after calibration.
A drop of urine should then be placed on the refractometer prism and the cover closed. The refractometer should be held horizontally in the direction of a good light source. The result should be read as where the colour line is against the specific gravity scale. After the use the prism should be cleaned using a damp lens wipe.
These tests are a method of monitoring major chemicals in the urine. The dipsticks are designed to be used on human urine and some of the tests are not suitable for use with animal urine- e.g. SG, nitrite and leucocyte activity.
Fresh in date test sticks should always be used and the test pads must not be touched directly with the fingers. A drop of urine should be applied to each test square using a pipette or 1ml syringe. The colour changes should be checked and compared with the test chart provided at the times indicated in the instructions of the sticks.
Urine sediment analysis
A fresh urine sample should be placed in a conical centrifuge tube and centrifuged at approx. 1000rpm for 5 minutes. The supernatant should then be decanted. A specialised urine stain such as Sedistain should then be added to the remainder and mixed. A drop of the resultant solution should be placed on a microscope slide and a coverslip placed over it. The slide should be placed under a microscope and scanned at X10 magnification for the presence of crystals. The slide should then be rescanned at X40 magnification to record the numbers of blood cells, casts, and epithelial cells.
Urine protein to creatinine ratio
Urine protein to creatinine ratio needs to be measured at an external lab. It provides information about how much protein is being lost in the urine, independent of the concentration of the urine. High UPC values are associated with high levels of protein in the urine, most commonly due to glomerular kidney disease.
In healthy cats, the urine protein to creatinine ratio (UP:UC) is usually <0.5.
Values between 0.5-1.0 in non-azotaemic cats are considered equivocal and continued monitoring for progression is recommended.
Values >1.0 in non-azotaemic cats are abnormal and diagnostic evaluation is warranted.