Accuracy of PSA tests

PSaA is measured in nano-grams per millilitre and is normally in the range of 0.1 to 4. There are two forms of PSA present in the bloodstream, those bound to alpha antichymotrypsin, which are the most abundant form, and free PSA. It is generally considered that by analyzing the percentage of free PSA together with total PSA (defined as percent-free PSA) will lead to more accurate diagnostics of the chance of a patient having prostate cancer.

Patients with PSA test results of between 4 and 10 are normally considered borderline patients; the level of percent free PSA well then determine if a biopsy is required. If percent-free PSA numbers are 10% or less then the chance of having cancer is about 50%. Normally a doctor will recommend a patient has a biopsy if percent-free PSA readings are less than 25%.

It is recommended that both a digital rectal examination and a Protein specific antigen test are carried out together. This is because of the nature of detection of specific cancers, has been reported that if a digital rectal exam alone is taken that 60 percent of the detected cancers are advanced whereas when a PSA test is also performed this level reduces to 33%.