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A complete urinalysis includes physical, chemical, and microscopic examinations. Midstream clean collection is acceptable in most situations, but the specimen should be examined within two hours of collection. Cloudy urine often is a result of precipitated phosphate crystals in alkaline urine, but pyuria also can be the cause. A strong odor may be the result of a concentrated specimen rather than a urinary tract infection. Dipstick urinalysis is convenient, but false-positive and false-negative results can occur. Specific gravity provides a reliable assessment of the patient's hydration status. Microhematuria has a range of causes, from benign to life threatening. Glomerular, renal, and urologic causes of microhematuria often can be differentiated by other elements of the urinalysis. Although transient proteinuria typically is a benign condition, persistent proteinuria requires further work-up. Uncomplicated urinary tract infections diagnosed by positive leukocyte esterase and nitrite tests can be treated without culture. (Am Fam Physician 2005;71:1153-62. Copyright© 2005 American Academy of Family Physicians.)
Urinalysis is invaluable in the diagnosis of urologic conditions such as calculi, urinary tract infection (UTI), and malignancy. It also can alert the physician to the presence of systemic disease affecting the kidneys. Although urinalysis is not recommended as a routine screening tool except in women who may be pregnant, physicians should know how to interpret urinalysis results correctly. This article reviews the correct method for performing urinalysis and the differential diagnosis for several abnormal results.
Specimen Collection
A midstream clean-catch technique usually is adequate in men and women. Although prior cleansing of the external genitalia often is recommended in women, it has no proven benefit. In fact, a recent study1 found that contamination rates were similar in specimens obtained with and without prior cleansing (32 versus 29 percent). Urine must be refrigerated if it cannot be examined promptly; delays of more than two hours between collection and examination often cause unreliable results.2
Physical Properties: Color and Odor
Foods, medications, metabolic products, and infection can cause abnormal urine colors (Table 1).3 Cloudy urine often is a result of precipitated phosphate crystals in alkaline urine, but pyuria also can be the cause.
The normal odor of urine is described as urinoid; this odor can be strong in concentrated specimens but does not imply infection. Diabetic ketoacidosis can cause...