Point of care (POC) diagnostic tests for chlamydia have low sensitivity and positive predictive value, a study from the Netherlands has found.

The researchers evaluated the diagnostic performance of three POC tests: Handilab-C, Biorapid CHLAMYDIA Ag test and QuickVue Chlamydia test comparing them with the nucleic acid amplification test (NAAT), the gold standard for diagnosing chlamydia.

All the POC tests were commercially available and had a CE mark (Conformitée Européene).

A total of 772 women over the age of 16 attending for STI consultation, between September 2007 and April 2008, in Maastricht were studied. Each woman was given six self-sample vaginal swabs (SVS), labelled 1-6, with explicit instructions on sampling techniques. Demographic and behavioural data were collected during the consultation. All data were anonymised and samples transported to the hospital laboratory. Women who tested positive were treated with 1 g of azithromycin.

SVS 3 to 5 were used for POC tests. The order of tests was randomised to reduce bias from sampling variation. SVS 2 was used for NAAT; SVS 1 and 6 were used to determine quantitative chlamydia load for validation.

The prevalence of chlamydia was 11%. Sensitivities of Biorapid CHLAMYDIA Ag test, QuickVue Chlamydia and Handilab-C test were 17%, 27% and 12% respectively.

The WHO has formulated ASSURED criteria for a POC test:

• affordable by those at risk
• sensitive (between 43% and 65%)
• specific (98%)
• user friendly
• rapid
• robust
• equipment-free
• deliverable to those in need

The ASSURED criteria were not met by any of the POC tests investigated.

The authors described these tests as having ‘alarmingly poor performance' particularly in terms of sensitivity and positive predictive value; they also state that these tests are not ready for widespread use. Clearly in practice, this would result in infections being missed and unnecessary treatment for those with false-positive results.

The accompanying editorial, from the UK, also highlights the fact that the CE mark is not a guarantee of diagnostic accuracy. In order to obtain the mark, the manufacturer has to demonstrate that their test is comparable with those already CE marked; this depends on the test used as a comparator and does not ensure the most up-to-date standards for sensitivity and specificity.

It is worrying that at least one of the tests is currently available on the internet for self-testing.

Not only is the performance of the tests a concern, but the effectiveness of the public to carry out these tests, interpret the results and get timely advice and treatment remains unknown.

Dr Richard Ma