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Prostate Cancer (cont.)

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What are false positive elevations in the PSA test?

False-positive elevations in the PSA are increases in the PSA that are caused by conditions other than prostate cancer. For example, benign prostatic hyperplasia (BPH) and infection or inflammation of the prostate (prostatitis) from whatever cause can elevate the PSA. Note also that even a rectal examination or an ejaculation within the prior 48 hours can sometimes elevate the PSA. False-positive elevations are usually in the 4 to10 range, but they can go as high as 25 or 30. At these higher levels, however, caution in the interpretation of the test is warranted because a prostate cancer may well be present. Non-prostatic diseases or infections, medications, foods, smoking, and alcohol do not cause false-positive elevations of the PSA.

The ability of the PSA test to detect prostate cancer (called the sensitivity of the test) is high. The reason for this is that most patients, although not all, with prostate cancer have a borderline or an abnormally elevated PSA. The ability of the test to exclude other diagnoses (called the specificity of the test), however, is lower because of the other conditions that can cause false-positive elevations of the PSA.

What refinements have been made in the PSA test?

Recently, several refinements have been made in the PSA blood test. The purpose of these refinements is to help doctors to better assess a borderline or an elevated PSA. The goal is to determine more accurately who has prostate cancer and who has a false-positive elevation of the PSA from another condition. In other words, the purpose of the improvements is to improve the sensitivity and the specificity of the test.

One refinement is called the PSA ratio. This ratio is determined by dividing the amount of PSA that circulates freely in the bloodstream by the amount of PSA that is bound to proteins in the bloodstream. Research has shown the PSA that circulates freely in the blood tends to be associated with benign prostatic hyperplasia (BPH) whereas the PSA that is bound to protein tends to be linked with prostate cancer. Thus, a high PSA ratio suggests a false-positive elevation of the PSA and weighs against the diagnosis of prostate cancer. In contrast, a high PSA with a low PSA ratio favors the diagnosis of prostate cancer.

Another recent modification of the PSA test is based on the observation that as men age the amount of PSA in the blood can normally rise without the presence of a prostate cancer. Thus, doctors can use what is referred to as an age-specific PSA, especially to evaluate borderline values. In the age-specific PSA, the normal values are adjusted for the age of the patient. Accordingly, the age-specific normal ranges are 0 to 2.5 for men in their 40s, 0 to 3.5 in their 50s, 0 to 4.5 in their 60s, and 0 to 6.5 for men 70 years of age and over. Therefore, as an example, a PSA of 4 would be considered borderline for men in their 30s and 40s but could be normal for men in their 50s, 60s, and 70s.

Furthermore, another improvement of the PSA test is called the PSA velocity or slope. The velocity is calculated as the rate at which the PSA changes with repeated testing over time. The more rapid the rise in the PSA, the more likely is the presence of a prostate cancer. The less rapid the rise in the PSA, the less likelihood there is that a prostate cancer is present.

Prostate cancer gene 3 (PCA3) is a new gene-based test carried out on a urine sample. PCA3 is highly specific for the diagnosis of prostate cancer. Therefore, in contrast to PSA, the PCA3 is not increased by conditions such as benign enlargement or inflammation of the prostate. The PCA3 urine test can provide additional information over a PSA test that may help in deciding whether a prostate biopsy is really needed.

Medically Reviewed by a Doctor on 12/9/2013

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