By Michelle Roberts
Health reporter, BBC News
The tests have been on sale in pharmacies
A faulty self-testing kit on sale in the UK for prostate cancer could mean some given the all clear actually have cancer, a government agency is warning.
Two brands available to buy in pharmacies and online since December 2008 are involved, says the MHRA.
A thousand kits of Fortel's PSA test and Simplicity Health's prostate screening test are affected.
But experts say any man who has used either brand during this time should consider getting retested.
Affected kits have an expiry date of September 2010 and the lot number 1012.
The tests look for elevated levels of Prostate Specific Antigen or PSA present in the blood.
PSA is a chemical that appears in the bloodstream in higher concentrations when the gland is enlarged or cancerous.
US manufacturer, Biomerica Inc, notified the MHRA of the recall after an in-house study showed up the problem.
Sales of the kits have been suspended. Pharmacies and GPs have received an alert about the error and are being asked to advise customers and patients to consider getting re-tested.
A spokeswoman for the MHRA said: "The advice to anyone concerned is to see your GP and get re-tested.
"One thousand kits were affected, but if you buy a home test kit you do not keep the packaging so it is hard to tell how many men this will impact."
A spokeswoman for Biomerica Inc said: "No diagnostic test is 100% perfect and there are sufficient warnings in the packs saying that whether you test positive or negative you should follow up with your doctor for regular exams and testing."
In the UK and other European countries, PSA testing is not recommended for screening for a number of reasons.
These include the fact that some men with prostate cancer do not have a raised PSA level and two out of three men with a raised PSA do not have cancer.
Also, there is uncertainty about the best way to treat early prostate cancer - the treatments can cause unpleasant side effects and some cancers are very slow growing and will never cause any symptoms or problems in their lifetime.