Purpose: The optimal interval at which to repeat prostate-specific antigen (PSA) measurement is controversial. We evaluated the probability of the serum PSA value increasing above specific cutoff values (4.0 ng/ml, 3.0 ng/ml, and 2.5 ng/ml) on annual follow-up visits in men with a lower baseline PSA than each cutoff value. Materials and Methods: Between 2002 and 2006, a total of 14,459 men aged 40 to 79 years who underwent serum PSA determinations at least twice during health examinations at 11 medical centers were enrolled in this study. To reduce probable bias, we excluded men with pyuria, those with a baseline or follow-up PSA level of 10.0 ng/ml or more, and those with a history of medication with 5 alpha-reductase inhibitors. Serum PSA underwent logarithmic conversion to work out the normal distribution. The cumulative rate of freedom from increase in PSA above 4.0 ng/ml, 3.0 ng/ml, and 2.5 ng/ml was estimated with the Kaplan-Meier method according to baseline PSA range and age. The significance level was 1%. Results: The rate of increase in PSA was lower in men who had a baseline PSA value in the low range and whose age was in the 40s or 50s. However, the cumulative rate of freedom from increase in PSA decreased as the PSA cutoff value was lowered. The optimal screening interval for men in their 40s and 50s whose baseline serum PSA level was 1.0 ng/ml or lower was 3 years when the significance level for PSA rising above 4.0 ng/ml was 1%. It was 2 years and 1 year, respectively, when the cutoff value was lowered to 3.0 ng/ml or 2.5 ng/ml. An annual PSA screening interval was recommended in men older than their 60s. Conclusions: The PSA test interval should be individualized according to baseline PSA, age, and PSA cutoff value.
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