The PSA test

Last week I went for a blood test at the Royal Free Hospital and  will get my PSA score at the clinical meeting this Tuesday. I thought it might be a good idea therefore, to write something about the PSA test.

Prostate-specific antigen (PSA) is a protein produced by cells of the prostate gland. A blood sample is sent off to a laboratory which measures the level of PSA in the blood. Normally the PSA level should be low, but prostate cancer or benign (non cancerous) conditions can increase the PSA level. It is important to note that the PSA test is not a measure of cancer but just an association that might indicate problems. In fact the most frequent reason for an elevated PSA level is a benign prostate condition such as  prostatitis (inflammation of the prostate) or benign prostatic hyperplasia (BPH) (enlargement of the prostate).

If a doctor receives an elevated score for a patient he may well decide to undertake a DRE to try to ascertain whether the cause is likely to be the presence of cancer or a benign condition.

One important fact is that men who are on hormone therapy for prostate cancer will have often a misleadingly low PSA level. It is not unusual for doctors to work on the basis that the test score will need to multiplied by a factor of up to four to get a more realistic reading.

Up to fairly recently a result of over 4.0 ng/mL (nanograms per milliliter) was considered the threshold for further investigation. However, there is currently some thought that this threshold should be reduced to 2.5 ng/mL, but there is no ’normal’ level. Various factors, such as inflammation (e.g., prostatitis), can cause the PSA level to fluctuate. More worryingly it is also common for PSA values to vary somewhat from laboratory to laboratory.

Given these limitations there is considerably effort being put in to find a better test. Scientists are also researching ways to improve the PSA test, hopefully to allow cancerous and benign conditions to be distinguished from one another.