The prostate-specific antigen blood test measures the level of prostate-specific antigen in a man’s blood. A prostate-specific antigen blood test is part of routine prostate cancer screening for most men older than 50. If the test result shows a moderately elevated prostate-specific antigen level, a referral for a biopsy is usually recommended. However, evidence now suggests that biopsy should not be performed until the test is repeated, because prostate-specific antigen levels commonly fluctuate above and below the normal range.
Although the prostate-specific antigen test is a sensitive diagnostic assessment of prostate cancer, it is not flawless; high prostate-specific antigen levels can be caused by other conditions than malignancy. Although it is not perfect, and many flag a high number of men who do not have prostate cancer, recent studies have found that prostate cancer screening has increased survival rates.
Prostate-specific antigen was discovered in the 1970s by Japanese and American scientists; it was named in 1979 by Dr. Ming Wang. The next year, Dr. Wang and his colleague Lawrence Papsidero created a blood test to assess prostate-specific antigen levels, which was approved by the U.S. Food and Drug Administration in 1985. The test was first used simply to figure out whether treatments for prostate cancer were effective: If the prostate-specific antigen level dropped, the treatment was considered to be successful. Today its use has been broadened to detect cases of early prostate cancer as well as assess treatment success.
Free Prostate-Specific Antigen Test
Prostate-specific antigen can occur in two forms in the blood: as bound prostate-specific antigen, in which the prostate-specific antigen is attached to proteins, or free prostate-specific antigen, in which it is not attached. In addition to the regular prostate-specific antigen test, a doctor can use the newer free prostate-specific antigen test, which measures the inactive form of the antigen. The free prostate-specific antigen test is about twice as expensive as the standard prostate-specific antigen test. A free prostate-specific antigen value above 25 percent suggests that prostate cancer is less likely; a score of 15 percent or below means the chance of cancer is higher.
In cases of a mildly elevated prostate-specific antigen level (between four and 10), the free-to-bound prostate-specific antigen ratio may help a doctor decide whether or not to perform a biopsy. The higher this ratio number, the less likely that there is prostate cancer; the lower the percentage score, the worse the outlook.
High Prostate-Specific Antigen Levels
A number of factors can increase the prostate-specific antigen level, including anything that irritates the prostate gland, such as a urinary tract infection, recent use of a urinary catheter, prostate stones, a recent prostate biopsy, a vigorous rectal exam, urinary retention, prostatic massage, or prostate surgery. Even sexual ejaculation can increase the level by up to 10 percent.
Benign prostatic hyperplasia may increase the prostate-specific antigen level because in a larger prostate more prostate cells are present to produce more prostate-specific antigen. However, the condition of benign prostatic hyperplasia tends to produce lower levels of prostate-specific antigen than does prostate cancer. And because the prostate continues to grow as men age, the prostate-specific antigen level may continue to increase slightly from year to year. However, some experts believe that normal enlargement with aging should still not increase a man’s prostate-specific antigen level by more than 0.75 ng/ml a year or by more than 20 percent of the previous level.
The prostate-specific antigen test is very sensitive, and because any inflammation or irritation of the prostate can affect prostate-specific antigen level, the prostate-specific antigen test result may fluctuate in men who do not have prostate cancer. In a 2003 study published in the Journal of ‘the American Medical Association, researchers at Memorial Sloan-Kettering Cancer Center and colleagues studied nearly 1,000 men who had five consecutive prostate-specific antigen tests over a four-year period. Up to one-third of these men had an elevated prostate-specific antigen level, a finding that usually prompts a referral for a prostate biopsy. However, subsequent testing of the same men a year or more later indicated that the prostate-specific antigen level of half of the men had returned to normal. Had a biopsy been performed, it might have been unnecessary.
Researchers concluded that a single elevated prostate-specific antigen level does not automatically warrant a prostate biopsy. Instead, experts recommend having the findings confirmed by repeating the prostate-specific antigen test after waiting at least six weeks. Even if the repeat test shows an elevated level, prostate cancer is discovered in only about one-quarter of men who have a biopsy. A policy of confirming newly elevated prostate-specific antigen levels several weeks later may reduce the number of unnecessary procedures as well as the number of men diagnosed with a small incidental tumor that poses no threat to life or health. Waiting to confirm the diagnosis does not have a negative effect on those men who actually have prostate cancer, experts note, because a delay in diagnosis of a few weeks or months is unlikely to alter treatment outcome.
Frequency Of Prostate-Specific Antigen Screening
The American urologic association and the American College of Surgeons recommend that most men start prostate cancer screening at the age of 50. However, these experts suggest that African Americans and men who have a family history of prostate cancer start screening at age 40. Not every expert agrees with these recommendations. The American Academy of Family Physicians questions the wisdom of annual testing, concerned that it may lead to excessive biopsy procedures among men who do not have prostate cancer. They point to the fact that a mild elevation (up to four) in level is not cancer about 70 percent of the time.
In addition, some doctors determine the frequency of required screenings by comparing the prostate-specific antigen level to the size of a man’s prostate gland (prostate-specific antigen density). Usually a high prostate-specific antigen level in a man who has a small prostate gland is more of a concern than the same prostate-specific antigen level in a man who has a larger prostate. The higher the prostate-specific antigen density, the more concern there is for prostate cancer.
Those Who Do Not Need Prostate-Specific Antigen Testing
Study results suggest that not all men, specifically those who have a prostate-specific antigen level less than two, benefit from annual prostate-specific antigen screenings. Older men with limited life expectancy are also unlikely to benefit from screening.
Drugs and prostate-specific antigen Levels
Any drug that affects the size of the prostate or the amount of testosterone produced by the testicles affects prostate-specific antigen level. Finasteride (Proscar), a medication used to help shrink a prostate enlarged as a result of benign prostatic hyperplasia, decreases the prostate-specific antigen level by up to 50 percent. This decrease occurs when a man uses this drug, regardless of the baseline. Any steady increase of prostate-specific antigen that occurs while taking this medication must be evaluated immediately. The percentage of free prostate-specific antigen should not decrease while taking this drug.
Medications that decrease the testosterone level may cause prostate tissue to shrink and therefore also lower prostate-specific antigen level. Alternatively, boosting testosterone level may stimulate the growth of both normal and malignant prostate cells. Although testosterone therapy has not been shown to trigger the development of prostate cancer, it is known that prostate cancer is composed of cells, some of which are and some of which are not sensitive to hormones. The cells not sensitive to hormones grow regardless of the testosterone level, but the hormone-sensitive cells may be affected by testosterone level.
Therefore, men who are having testosterone therapy have a theoretical risk that the testosterone may cause an undetected prostate cancer to grow. For this reason, men who use this drug treatment should have a digital rectal exam and a prostate-specific antigen level test every six months (instead of yearly). Any significant increase in prostate-specific antigen level or change in rectal exam results during testosterone therapy requires evaluation.
Having the Test
A prostate-specific antigen test should ideally be performed by the same lab each time, since different labs may use different forms of prostate-specific antigen tests.