Evaluation of the urine for its physical and chemical properties, and microscopic sediment examination are important components of the clinical and laboratory examination of any healthy or ill patient. The components of a routine urinalysis include appearance, specific gravity, pH, protein and glucose content, bilirubin, presence of ketones or glucosuria, presence of occult blood, and examination of the urinary sediment for the presence of leukocytes, erythrocytes, epithelial cells, casts, bacteria, yeast, fungi, and crystals. In addition, renal function is assessed in the routine blood chemistry profile by measurements of BUN, creatinine, electrolytes, amylase, and albumin in the case of persistent proteinuria.

Urine can be collected by cystocentesis, catheterization, and midstream free catch (voided). However, voided midstream collections usually yield adequate specimens only if results are negative, as interpretation of cell counts, protein content, and culture of these specimens may give misleading results. The presence of bacteria in urine collected by cystocentesis indicates an infectious process, whereas bacteria may be present in varying numbers in catheterized or midstream voided samples. In the latter situations, these organisms are usually contaminants during the collection process.

Routine transport time does not influence urinalysis or urine culture results, if the sample has been collected appropriately and placed in the correct type of sterile container [see below].

Published information from a study of urine collected from 31 healthy dogs and eight healthy cats assessed the effects of storage time and temperature on pH, specific gravity, and crystal formation. All the cat samples were collected by cystocentesis, whereas most of the dog samples were obtained by midstream free catch (27); the remaining four urines were collected by cystocentesis (2) and catheterization (2). Aliquots of each urine sample were analyzed within 60 min of collection and after storage at room or refrigeration temperatures for six and 24 hrs. Results indicated that crystals formed in samples from 11 of the animals (28%), but that increased storage time and decreased storage temperature were associated with a significant increase in the number of calcium oxalate crystals formed. Greater numbers of crystals formed in the urine aliquots stored for 24 hrs than in those stored for six hrs. There was no significant effect of storage time and temperature on pH or specific gravity. The conclusions of the study were that urine sample should be analyzed within 60 min of collection to minimize temperature- and time-dependent effects on in vitro crystal formation. Presence of crystals observed in stored samples should therefore be validated by reevaluation of fresh urine.

Crystals commonly are present in the urine of dogs and cats and usually are of little diagnostic significance. Struvite, amorphous phosphates, and oxalates are examples of crystals that may be found in normal urine samples.