The normal range of values is generally considered to be 0 to 4 ng/mL (nanograms per milliliter of serum), with higher values prompting further investigation and testing. However, questions have been raised about the upper level of this standard because a significant number of older men in the general population, whose values exceed the range, may have received more extensive testing than necessary.
To determine the association between age and PSA values, a study was conducted among 422 healthy men age 40 to 79 years in Olmsted County, Minnesota. These men were determined to be free of prostate cancer, based on detailed clinical examinations that included a digital rectal examination, PSA testing, and a transrectal ultrasound.
The values of the PSA testing correlated directly with age. The distribution of the values was examined and the 95th percentile was identified for each age decade. The use of the 95th percentile value in the disease-free portion of a population would, conceptually, result in 95 percent of disease free men being correctly identified as disease free and 5 percent of disease free men at all ages would be subject to further testing. This study did not address the converse; that is, they did not examine diseased men to determine what percent of that population would have PSA values within the normal range and, therefore, might not be referred for further testing.
The experiment identified the age-specific distribution of PSA values among the LSAH participants, both astronaut and comparison, and identified what percent of this population would not be routinely referred for further testing using the age-specific-range of values recommended by the Olmsted County study. For the purposes of this report, only PSA values were used. Therefore, the comparison is between a disease-free (Olmsted County study) population and the LSAH population without any prior assumption being made about the disease status of the LSAH population. The most recent test for each individual was included in these analyses. A total of 428 men (295 comparisons and 133 astronauts) have PSA results from their most recent physical examination.
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