Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1168 page)

   Dopamine agonists

   Ergot derivatives (bromocriptine mesylate, lisuride hydrogen maleate)

   Levodopa, apomorphine, clonidine

   Limitations

   Normal prolactin secretion varies with time, which results in serum prolactin levels two to three times higher at night than during the day.

   The biologic half-life of prolactin is approximately 20–50 minutes. Serum prolactin levels during the menstrual cycle are variable and commonly exhibit slight elevations during the mid-cycle.

   Prolactin levels in normal individuals tend to rise in response to physiologic stimuli including sleep, exercise, nipple stimulation, sexual intercourse, hypoglycemia, pregnancy, and surgical stress.

   Prolactin values that exceed the reference values may be due to macroprolactin (prolactin bound to immunoglobulin). Macroprolactin should be evaluated if signs and symptoms of hyperprolactinemia are absent or pituitary imaging studies are not informative.

PROSTATE-SPECIFIC ANTIGEN (PSA), TOTAL AND FREE

   Definition

   PSA is a glycoprotein that is expressed by both normal and neoplastic prostate tissue and is prostate tissue specific and not prostate cancer specific. PSA is consistently expressed in nearly all prostate cancers, although its level of expression on a per cell basis is lower than in normal prostate epithelium. The absolute value of serum PSA is useful for determining the extent of prostate cancer and assessing the response to prostate cancer treatment; its use as a screening method to detect prostate cancer is also common, although controversial.

   PSA exists primarily as three forms in serum. One form of PSA is enveloped by the protease inhibitor, alpha-2 macroglobulin, and has been shown to lack immunoreactivity. A second form is complexed to another protease inhibitor, alpha-1 antichymotrypsin (ACT). The third form of PSA is not complexed to a protease inhibitor and is termed “free PSA.” The latter two forms are immunologically detectable in commercially available PSA assays and are referred to collectively as “total PSA.”

   Free PSA values alone have not been shown to be effective in patient management and should not be used. Both total PSA and free PSA concentrations should be determined on the same serum specimen and used to calculate the percentage of free PSA. Percent free PSA values are then used for patient management.