From the point of view of a hospital doctor, the laboratory tests previously described have considerable advantages. They give exceptionally accurate results, processes are automated and quality control can be assured in a laboratory environment. Also, if a test appears to give either a positive result or one that is difficult to interpret, there is plenty of time to carry out additional tests to clarify the diagnosis.

But laboratory tests have some disadvantages, especially from the point of view of people testing. Some people dislike having blood taken with a needle. Getting the results usually requires coming back on another day, something that a lot of people fail to do. Laboratory tests tend to be offered in hospital settings.

“Point-of-care” tests (PoCT) do not require specialised laboratory equipment, so they can be administered and interpreted in any setting. Most point-of-care tests require a tiny sample of blood (the fingertip is pricked with a lancet). Other tests require oral fluid (an absorbent pad is swabbed around the outer gums, adjacent to the teeth). They are called “rapid” tests because the result can usually be given within 30 minutes. These tests are often used in community settings on the assumption that more people will be willing to test for HIV if they can do so at venues they go to anyway.

However, some doctors and laboratory professionals are wary of using these tests and note inferior performance to antibody/antigen laboratory tests. While several studies have shown point-of-care tests to be almost as accurate as antibody laboratory tests, performance has not always reached these standards.

Rapid tests can be performed by staff with limited laboratory training. However, reading the test result relies on subjective interpretation, and when the result is borderline, experienced staff give more consistently accurate results. Poor results in some studies might be due to problems with staff training or quality control, rather than intrinsic limitations of the tests. But this does highlight real-world difficulties in delivering consistently reliable results. Organisations using point-of-care tests must maintain strong links with a pathology laboratory that provides support with clinical governance and quality assurance.

The UK testing guidelines – issued by the British HIV Association (BHIVA) and the British Association for Sexual Health and HIV (BASHH) – are cautious about the use of point-of-care tests, recommending that they are only used:

• At community testing sites.
• In clinical settings where a rapid turnaround of test results is desirable.
• For urgent source testing (for example, following a needlestick injury).
• If a person refuses to give a venous blood sample.

The guidance from NICE (the National Institute for Health and Care Excellence) is more supportive of the use of point-of-care tests, for example in outreach testing programmes in high-prevalence areas and also in venues where high-risk sexual behaviour between men occurs. 

When used in a population with a low prevalence of HIV, false-positive results can be a problem. The tests always produce a small number of false positive results, but in a setting where very few people have HIV, the majority of apparent positive results will in fact be incorrect. However, as the proportion of people with HIV being tested increases, the true positives start to outnumber false positives. This means it is more appropriate to use point-of-care-tests in high-prevalence populations, such as with gay and bisexual men, than in the general population.

As noted above, all HIV tests need to have reactive (“positive”) results confirmed with further tests. Most providers tell people who are testing that a negative result is definitive, but that a reactive result simply indicates the need for further laboratory testing.