Prostate Specific Antigen (PSA) Tests

Survey of Prostate Specific Antigen Tests (PDF 101Kb)

Second Survey of Prostate Specific Antigen Tests (PDF 121 Kb)

Prostate Specific Antigen (PSA) exists in different forms (isoforms). It can be joined to other proteins when it is often referred to as complexed PSA, or it can exist on its own, known as free PSA.

The PSA tests commonly referred to and used in Prostate Cancer Risk Management are total PSA tests. This means that they detect both free and complexed PSA to give a measure of all PSA present in the blood sample.

Total PSA tests used in Prostate Cancer Risk Management to measure PSA levels in men with no symptoms of prostate disease, have to meet certain quality criteria. There is ongoing work with the NHS Centre for Evidence-based Purchasing to regularly evaluate PSA tests against these criteria.

A report of the most recent findings is available, Evaluation Report - Total PSA Assays (PDF 76Kb).

PSA tests that measure only free or complexed PSA do exist. The relative proportions of free and complexed PSA are thought to be different in men with prostate cancer when compared to men with other prostatic diseases where the total PSA level is also raised. Men with cancer are thought to have a smaller proportion of free PSA and more complexed PSA than men with other benign prostatic diseases such as benign prostatic hyperplasia (BPH) or prostatitis.

Free or complexed PSA tests are provided by some laboratories. They are often used as follow on tests following a raised total PSA test result. The results are reported as the percentage of free PSA compared with the total amount of PSA detected. Any results below a cut-off value are thought to be suggestive of prostate cancer. These free or complexed PSA tests are designed to be used when the total PSA test result is marginally raised, and not in cases where the total PSA test result is very high and suggestive of advanced prostate cancer.

How much testing for prostate cancer is taking place in England and Wales?

There are no routinely collected data in the UK with which to monitor or study the extent to which men are being tested for prostate cancer. These data are important if we wish to know the amount of testing that is taking place, its impact on the workload of the NHS and future changes in incidence of and mortality from prostate cancer.

The Policy Research Programme of the Department of Health funded an independent investigation of the rate of Prostate Specific Antigen (PSA) measurement in general practice in England and Wales. The study was conducted by the Cancer Screening Evaluation Unit at The Institute of Cancer Research in association with 28 pathology laboratories and over 300 general practices. The aim of the study was to investigate the rate of PSA testing in asymptomatic men and to study factors associated with variation in the rate of testing within general practice. The overall annual rate of testing in men with no prior diagnosis of prostate cancer was estimated to be 6.0 per 100 men, of which the annual rates of asymptomatic testing, symptomatic testing and re-testing were 2.0, 2.8 and 1.2 per 100 men respectively after adjusting for missing values. The rate decreased with increasing social deprivation, and increasing proportions of black and Asian populations. The overall rate of PSA testing increased significantly from 1999 to 2002. If the recommendations of the NHS Prostate Cancer Risk Management Programme were applied, 14% of asymptomatic tests and 23% of symptomatic tests would have led to referral. As the rate of PSA testing is rising and there are uncertainties about the benefit of screening, the workload and costs in general practice and hospitals should be monitored.

A peer review paper has been published in the British Journal of Urology International¹. The full report of the study has also been peer-reviewed by the Department of Health and has been made available to the Prostate Cancer Risk Management scientific reference group.

Reference
¹Melia J, Moss S, Johns L, and contributors in the participating laboratories. Rate of Prostate Specific Antigen testing in general practice in England and Wales in asymptomatic and symptomatic patients: a cross-sectional study. BJU Int 2004:94; 51-56.

If you are worried about a specific problem, or otherwise worried about the risks of cancer, then you should talk to your GP.