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COPYRIGHT 2003 Jannetti Publications, Inc.
This is the first of a two-part article reviewing basic laboratory, imaging, endoscopic, urodynamic, and miscellaneous studies used for screening and diagnosis of urologic disease. Normal values, recommended collection procedures, and interpretation of results are also reviewed. This initial installment deals with laboratory tests used in urologic disease.
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Investigating urologic disease involves many testing modalities, all driven by a thorough history and physical examination. Much of the evaluation is done in anticipation of surgery, or to followup after a surgical intervention. There is considerable overlap between other medical subspecialties and urology that may lead to a multidisciplinary evaluation. For example, abnormalities in renal clearance studies or evidence of stone disease may require the expertise of a nephrologist, or evaluation of erectile dysfunction may lead to an endocrinologic or cardiovascular etiology and referral. A comprehensive history and physical examination will define appropriate laboratory and diagnostic testing to aid in the diagnosis and treatment of urologic disease. Appropriate specimen collection, handling, and interpretation is imperative in utilizing laboratory results. Tests commonly used in evaluating urologic disease, as well as methods and caveats of performance and collection, will be reviewed.
BLOOD TESTING
Blood testing is useful in evaluating urologic disease, with emphasis on specific blood parameters. A complete blood count (CBC) is helpful to identify leukocytosis in suspected infection or anemias suggesting blood loss or chronic disease. A chemistry profile is also useful with levels of potassium, creatinine, uric acid, and magnesium giving clues about kidney function.
The most frequently used serum chemistry marker of disease in urologic disorders is creatinine. Creatinine is a byproduct of energy metabolism where creatine phosphate in muscle is broken down and excreted through the kidneys. Serum creatinine is used to screen for renal insufficiency in that it is elevated if renal function is impaired. It is more sensitive and specific than blood urea nitrogen (BUN) (in some laboratories, the value may be reported as urea nitrogen) in detecting renal disease, but BUN is useful to obtain the expected creatinine: BUN ratio (1:10). Increased creatinine levels can be forum in high ingestion of creatinine (meats), muscle disorders, shock, and dehydration. Decreased values are found in pregnancy, decreased muscle mass, advanced liver disease, and inadequate dietary protein. Creatinine may be elevated due to prerenal causes such as cardiac or vascular disease, intrinsic renal disease, and post renal causes such as bladder outlet obstruction. False depression occurs with high serum bilirubin and hyperglycemia, while false elevations may occur with ketoacidosis, high ascorbic acid intake, or use of cephalosporins. Renal function loss approaches 50% before the serum creatinine rises from 1.0 to 2.0 (Wallach, 2000).
Collection. The test involves obtaining a 5 ml venous blood sample.
Hormone Studies
Hormone studies are often used in evaluating genitourinary disorders. Testosterone is a sex hormone secreted by the adrenal glands and testes in men and by the adrenal glands and ovaries in women. It exists in serum in both the free form and bound to sex-hormone binding globulin (SHBG), and testosterone binding globulin. Only the free form is active. Serum levels are prone to large and rapid fluctuations, peaking in the early morning for males. Male levels of testosterone, particularly free testosterone, gradually decline with age as more of it...
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