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Study shows: ejaculation before PSA test can give false (higher) reading

In other words, don't have sex or masturbate at least a day before your PSA or you will get a false reading.


Herschman JD. Smith DS. Catalona WJ.

OBJECTIVES: Measurement of total serum prostate-specific antigen (PSA) is widely used as an aid to early detection of prostate cancer. Measurement of the ratio of free to total PSA may increase the specificity of PSA testing. To improve specificity further, other factors that may cause transient increases in PSA, such as ejaculation, have been identified. We prospectively studied the effect of ejaculation on total and free PSA levels and examined whether changes induced by ejaculation would affect recommendations for performing prostatic biopsy.

METHODS: We measured the baseline total and free serum PSA levels and obtained measurements 1.6, and 24 hours after ejaculation in 20 volunteers (mean age 59 years). All men had baseline PSA levels less than 4.0 ng/mL. We used repeated-measures analysis of variance to test for changes in total, free, and percent free PSA after ejaculation. We also calculated the proportion of men with PSA levels greater than the expected biologic variability at each timepoint.

RESULTS: The mean total, free, and percent free serum PSA increased 1 hour after ejaculation. Mean total PSA levels remained significantly increased 6 and 24 hours after ejaculation. Mean free PSA decreased to baseline levels by 6 hours after ejaculation, and percent free PSA returned to baseline by 6 hours after ejaculation and then decreased below baseline by 24 hours. When normal biologic variation was accounted for, 40% of men, at 24 hours after ejaculation, had total PSA levels above the baseline level. Similarly, 24 hours after ejaculation, the percent free PSA remained above baseline level in 10% and below baseline level in 35% of the men.

CONCLUSIONS: Both total and free PSA increase immediately after ejaculation, with differing rates of return to baseline levels. PSA testing within 24 hours after ejaculation may lead to an erroneous interpretation of the results of both total and percent free PSA measurements in a small proportion of men.

Urology. 50(2):239-43, 1997 Aug.

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