Daily variability in human serum prostate-specific antigen and prostatic acid phosphatase: a comparative evaluation.

The daily variation of serum levels of prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP) was investigated simultaneously in 10 patients with osseous metastatic prostatic cancer, 10 patients with benign prostatic hyperplasia, and 10 volunteers without prostatic disease. Duplicate serum samples were obtained from all patients on the same day at 8 AM, 12 PM, 4 PM, and 8 PM. Statistical analysis (two-factor analysis of variance comparing time period to disease group) of the mean PSA and PAP levels at the four sampling times on all patient groups demonstrated no evidence of circadian rhythmic variation or any other distinct pattern for the observed sample times. Overall, the variability in PSA levels was significantly less than that observed for PAP. There was no significant difference in mean percent variation between patient groups (cancer, benign, and normal prostate glands) for both the PSA and PAP assays. Our data reveal that serum PSA measurements fluctuate unpredictably over the course of a day in patients with and without prostatic disease, but to a lesser extent than that seen for serum PAP values. These findings illustrate the potential inaccuracy of single determinations of serum PAP or PSA levels for monitoring disease recurrence and treatment response in patients with prostate cancer.