Physiological variation of serum prostate specific antigen in the 4.0 to 10.0 ng./ml. range in male volunteers.
OBJECTIVE
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 week apart without any prostatic manipulation.


METHODS
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, automated Tosoh AIA-600 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).


RESULTS
Mean coefficient of variation (95% confidence limits) was 10.5% for between assay and 23.5% for physiological evaluations. The preferred analysis of ratio difference variation provided a factor of 0.138 (between assay) and 0.298 (physiological) for 95% confidence limits. Changes in free or complexed PSA were not the cause of physiological variation.


CONCLUSIONS
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 x 0.298) and still be within the physiological variability for 95% confidence limits.
Prestigiacomo
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AF
Department of Urology, Stanford University School of Medicine, California 94305-5118, USA.
Stamey
T A
TA
D001800:Blood Specimen Collection; D016001:Confidence Intervals; D006801:Humans; D007118:Immunoassay; D008297:Male; D008403:Mass Screening; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000517:prevention & control; D012016:Reference Values; D015203:Reproducibility of Results; D013997:Time Factors
D017430:Prostate-Specific Antigen