Examination of specimens of urine, blood, and genitourinary secretions or exudates commonly directs the subsequent urologic workup and frequently establishes a diagnosis*. Over 27 million outpatient visits per year are for common urologic diagnoses (Litwin and Saigal, 2012), and it is important for the physician to have a broad knowledge of the laboratory methods available to test appropriate specimens. Judicious use of such tests permits rapid, accurate, and cost-effective determination of the probable diagnosis and directs the management of patients with urologic disease.
Urinalysis is one of the most important and useful urologic tests available, yet all too often, the necessary details are neglected and significant information is overlooked or misinterpreted (Simerville et al, 2005). Reasons for inadequate urinalyses include (1) improper collection, (2) failure to examine the specimen immediately, (3) incomplete examination (eg, few laboratories perform a microscopic analysis unless it is specifically requested by the provider), (4) inexperience of the examiner, and (5) inadequate appreciation of the significance of the findings. There is no role for routine urinalysis for patient screening, and it should be reserved when clinically indicated, such as in patients with urinary tract symptoms or signs (Davis et al, 2012; Anonymous, 2012; Hagan et al, 2018). Studies indicate that macroscopic analysis (dipstick) has limited predictive value for urinary tract infection due to low sensitivity (44–77%) and specificity (66–87%), but it may be useful in specific situations, discussed below (Hessdoerfer et al, 2011; Little et al, 2009, 2010).
It is best to examine urine that has been properly obtained in the office or lab. First morning voided specimens are helpful for qualitative protein testing in patients with renal disease due to diabetes or hypertension, or in identifying benign orthostatic proteinuria (Witte et al, 2009). Urine specimens that are obtained immediately after the patient has eaten or that have been left standing for a few hours become alkaline and thus may contain lysed red cells, disintegrated casts, or rapidly multiplying bacteria; therefore, a freshly voided specimen obtained a few hours after the patient has eaten and examined within 1 hour of voiding is most reliable. The patient’s state of hydration may alter the concentration of urinary constituents. Timed urine collections (24-hour) may be required for definitive assessment of renal function or proteinuria. Examination of a urine specimen collected sequentially during voiding in several containers may help to identify the site of origin of hematuria or urinary tract infection.
Proper collection of the specimen is particularly important as it impacts interpretability of results. The specimen should be obtained before a genital or rectal examination in order to prevent contamination from the ...