Physiological Variation of Serum Prostate Specific Antigen in the 4.0 to 10.0 ng./ml. Range in Male Volunteers

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Abstract
Because some patients show a surprising variation in serial serum prostate specific antigen (PSA) values, we determined the intra-individual or physiological variation in serum PSA by collecting sera 2 to 3 weeks apart without any prostatic manipulation. Because 4.0 to 10.0 ng./ml. PSA is the critical range for decision making, we asked all men with a PSA in this range to return 2 to 3 weeks later for a second measurement. Total serum PSA was determined by the Hybritech Tandem-R, [dagger] automated Tosoh AIA-600 [double dagger] and Delfia [Section] immunoassays. Free and complexed serum PSA was determined by the Delfia assays. Between assay variation (first blood specimen retested on a separate day with the second blood specimen) was compared to the physiological variation (first versus second blood specimens). [dagger] Hybritech, Inc., San Diego, California [double dagger] Tosoh Medics, Foster City California [Section] Delfia, Turku, Finland Mean coefficient of variation (95 percent confidence limits) was 10.5 percent for between assay and 23.5 percent for physiological evaluations. The preferred analysis of ratio difference variation provided a factor of 0.138 (between assay) and 0.298 (physiological) for 95 percent confidence limits. Changes in free or complexed PSA were not the cause of physiological variation. The intra-individual physiological variation is 2 to 3 times the between assay variation for sera drawn 2 to 3 weeks apart with a PSA of 4 to 10 ng./ml. A serum PSA of 4.0 ng./ml. can increase to 5.2 ng./ml. (4.0 × 0.298) and still be within the physiological variability for 95 percent confidence limits.