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Urinalysis Health Article

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Urinalysis

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Definition

A urinalysis is a group of manual and/or automated qualitative and semi-quantitative tests performed on a urine sample. A routine urinalysis usually includes the following tests: color, transparency, specific gravity, pH, protein, glucose, ketones, blood, bilirubin, nitrite, urobilinogen, and leukocyte esterase. Some laboratories include a microscopic examination of urinary sediment with all routine urinalysis tests. If not, it is customary to perform the microscopic exam, if transparency, glucose, protein, blood, nitrite, or leukocyte esterase is abnormal.

Purpose

Routine urinalysis is performed for several reasons:

general health screening to detect renal and metabolic diseases
diagnosis of diseases or disorders of the kidneys or urinary tract
monitoring of patients with diabetes

In addition, quantitative urinalysis tests may be performed for diagnosis of many specific disorders, such as endocrine diseases, bladder cancer, osteoporosis, and phorphyrias. This often requires the use of a timed urine sample. Examples include the d-xylose absorption test for malabsorption, creatinine clearance test for glomerular function, the 24-hour urinary metanephrine test for pheochromocytoma, and the microalbumin test. The urinary microalbumin test measures the rate of albumin excretion in the urine using immunoassay. This test is used to monitor the renal vascular function of persons with diabetes mellitus. In diabetics, the excretion of greater than 200 μg/mL albumin is predictive of impending glomerular disease.

Voided specimens

All patients should avoid intense athletic training or heavy physical work before the test, as these activities may cause small amounts of blood to appear in the urine. Many urinary constituents are labile, and samples should be tested within one hour of collection or refrigerated. Samples may be stored at 2-8°C for up to 24 hours for chemical urinalysis tests; however, the microscopic exam should be performed within four hours, if possible. To minimize sample contamination, women who require a urinalysis during menstruation should insert a fresh tampon before providing a urine sample.

Over two-dozen drugs are known to interfere with various chemical urinalysis tests. These include:

ascorbic acid
chlorpromazine
L-dopa
nitrofurantoin (Macrodantin, Furadantin)
penicillin
phenazopyridine (Pyridium)
rifampin (Rifadin)
tolbutamide

Preservatives used to prevent loss of glucose and cells may affect biochemical test results. The use of preservatives should be avoided whenever possible.