The Prostate specific antigen - PSA test
Serine protease is an enzyme that is produced in the prostate. The levels of this enzyme, which is commonly known as prostate specific antigen and abbreviated to PSA, can be used to gauge the likelihood that the patient has developed prostate cancer. The PSA test is generally taken in parallel with the digital rectal examination to ensure more accurate diagnosis.
What is a PSA Test?
Men normally have a low level of PSA in the blood stream; levels of PSA can become elevated if prostate function is disrupted. Elevated PSA levels alone are not necessary an indicator of cancer, as infections of the prostate and benign growths may also lead to leakage of PSA into the bloodstream. Other factors that increase the prostate specific antigen levels in a PSA blood test include recent ejaculation and bike riding. In fact it has been recorded many times that patients with a high PSA score do not have cancerous growth of the prostate. The levels of PSA are also very dependent upon age and the size of the prostate, generally older people and larger prostates result in a naturally higher level of PSA’s. Conversely many drugs, such as those given to combat benign prostate hyperplasia can lead to a lowering of PSA levels and hence mask detection of cancerous growth.
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 a better psa test result interpretation and a 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 test 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%.
PSA Test References / further reading
Pepe et al, Should men with serum prostate-specific antigen < or =4 ng/ml and normal digital rectal examination undergo a prostate biopsy? Oncology . 2006;70(2):81-9.
American Cancer society PSA test section, 2007
Ilic et al, Screening for prostate cancer. : Cochrane Database Syst Rev. 2006 Jul 19;3