Abstract

Urinalysis is an essential part of general health screening because it provides information for systemic illnesses. The information obtained includes renal function, protein losing kidney disease, urinary tract disorders, polyuric disorders, diabetes mellitus, jaundice, acid-base, and even malignant diseases in the urinary tract and the prostate.

1. Indications

Urinalysis is a part of general health screening, and is considered to be as important as the CBC to detect systemic abnormalities in the body. It is not only for the screening of urinary system disorders, but also provides invaluable information for other organ systems. Therefore, it is always done when urinary disorders are suspected, but it should always be included in the initial screening when problems are to be determined. When it is performed, it is important that urinalysis should always be done in a certain constant procedure to give reliable results.

2. Urinalysis Procedures

a. Sample

Urine samples from voided urine, urinary catheter collection and cystocentesis can be used. It is best to obtain a cystocentesis sample, but voided urine can be used as the initial screening. The voided urine sample should be as fresh as possible, but it can be used up to 6 hours after collection when refrigerated, except for evaluation of crystals. It is important to make a note how the sample was collected. If there is no abnormal finding with the voided urine, the results can be valid and is recorded as the screening data. However, if there is any abnormal finding, the urinalysis should be repeated by using cystocentesis or catheter collection samples. Cystocentesis is the first choice in this situation, except for the case where coagulopathies are suspected or in the case where mild iatrogenic hemorrhage needs be avoided for critical evaluation of hemorrhage. Also, cystocentesis should be avoided when there is a suspicion of malignancy in the voided urine sediment. Urine should be collected by catheterization in such cases. Table 1 shows the parameters included in the urinalysis.

Table 1. Urinalysis test parameters

 Physical properties: Color, turbidity, odor, urine specific gravity.

 Chemical properties (multi-stick): pH, protein, glucose, ketones, occult blood, bilirubin.

 Urinary sediment: Cast, crystal, red blood cells, white blood cells, epithelial cells, bacteria, sperm, etc.

b. Physical Properties

The urine is first examined by vision and smell for color, turbidity, and odor. The intensity of the yellow color is related to the concentration of urine. Urine will be relatively dark-colored if there is dehydration, and in the case of polyuria and polydipsia (PU/PD) it becomes more colorless. Red urine suggests bleeding or hemolysis (or less frequently myoglobinuria). Bleeding usually gives a turbid red color as compared to hemolysis. An increase in bilirubin makes the color more greenish. Cloudiness indicates an increase in abnormal materials such as pus, crystals, or fat. Odor is not usually diagnostic, but a bad odor may indicate bacterial growth.

c. Urine Specific Gravity (USG)

The specific gravity of the urine is measured by using a refractometer. It should be noted that the specific gravity is converted from the refractory index, any increase in extra abnormal material in the urine can elevate the USG. For example, presence of a large amount of sugar in the urine can somewhat elevate USG even if there is polyuria and polydipsia (PU/PD). Thus, measurement of USG in the cloudy urine is not accurate. In such a case, a supernatant by centrifugation is used for the measurement. Also, it is important to note that conversion from the refractory index to USG is different in human, dog and cat. Therefore, it is recommended to use a refractometer which is validated for use in dogs and cats. The author recommends the use of a refractometer for veterinary use (www.heska.com). In case one uses a refractometer for human medicine, it is necessary to convert the reading for dogs or cats (Table 2).

Table 2. USG conversion table from human to dogs and cats (personal communication, Japanese manufacturer: ATAGO)

Urine specific gravity is an important assessment for hydration status, renal urinary concentration and dilution. It is important as to detect the decline of renal function, especially for early detection of chronic kidney disease. A USG between 1.008–1.012 is identical to the specific gravity of plasma, and it indicates that the kidneys are not performing their works either dilution or concentration, if it is seen constantly. This is a USG characteristic of chronic renal failure, and a constant forming of such urine is called isosthenuria. Insufficient concentration of urine, 1.013–1.029 in dogs and 1.013–1.034 in cats, if seen at multiple samplings, warrants diagnostic work-up for kidney disease. A low specific gravity of 1.007 or less indicates that the kidneys are working to dilute urine, and renal failure can be ruled out. The reasons for dilute urine production, however, should be investigated if the condition persists.

d. Chemical Analysis Using Multi-Stick Test Paper

A multi-stick test is a semi-quantitative dry chemistry analysis of the urine. In order to achieve a reliable quantitative test, it is important to regulate the sample volume and the time. The multi-stick is briefly dipped in the urine, the extra urine shaken off, and the time of the chemical reaction is accurately controlled. Combined with the color table in the exact time will now be determined. The color of the test paper in each parameter is then compared with the color chart supplied in the label of the bottle in exact time specified. Test parameters in multi-stick include pH, protein, glucose, ketone, occult blood, bilirubin. The multi-stick usually contains a parameter called urobilinogen, but it is not evaluated in veterinary medicine because it is less sensitive and specific in detecting cholestasis in dogs and cats.

e. Microscopic Examination of Urinary Sediment

A 5-ml sample of urine is centrifuged and urine sediment is used for microscopic examination. One drop of the sediment is placed on a glass slide, an 18 mm x 18 mm cover glass is placed, and the slide is examined unstained microscopically with a condenser aperture narrowed to have an extra contrast.

At a low magnification of 100x (10x objective lens) the slide is first examined to see what is present in the sediment. If there are urinary casts, the number is recorded. At a high magnification of 400x (40x objective lens), the type of cylinder, red blood cells, white blood cells, bacteria and other cells such as the epithelium are recorded (Table 3).

Table 3. Standard notation of the urinary sediment red blood cells and leukocytes in the x400 field (HPF)