HIV Testing using Antibody Tests


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The Human Immunodeficiency Virus (HIV) is the pathogen responsible for AIDS (Acute Immunodeficiency Syndrome), and is perhaps the most dangerous of all sexually transmitted illnesses (STI). The HIV virus and its resultant condition, called AIDS, is a very serious disease with no known cure, although management and treatment methods have improved dramatically in recent years. Because of how life altering and devastating the condition can be, HIV testing is extremely important both in terms of getting the treatment you need quickly, and in terms of making sure that the disease is not inadvertently transmitted, whether by sexual contact or some other exchange of bodily fluids (e.g. blood donation).

How is HIV tested for?

Testing for HIV is not as straightforward as most other STIs, where a simple urine test will often reveal the presence of the condition. HIV is made potent by the fact that the virus exists in different subtypes that are constantly changing, making the virus both hard to treat and detect. Because of how life changing a positive HIV test can be, particular care is taken to avoid false positives.

The primary method of diagnosing HIV is by way of a blood test that looks for the virus specifically. That being said, there are a number of different blood screens used to detect the virus, and each of these have their own pros and cons in terms of how reliably they can detect the virus. These include the ELISA and the Western Blot, two laboratory techniques commonly used both in the NHS and privately.

There are also quick and home testing options available, however these often need to be backed up with a traditional blood test.

When to take the HIV test

Timing is important when it comes to accurate HIV testing, and this can be tricky because once infected you may not show any signs of the disease for quite some time. The ‘window period’ is basically the time it takes between a point of infection until a test can accurately determine whether or not the virus is present. Typically speaking the window period for about HIV-1 (subtype B) tests is 25 days using antibody detection methods (antibodies in this case are HIV-specific immune molecules your body develops to defend yourself against HIV).

How long does it take to get an HIV result?

The type of test determines how long it takes to get a result, and it can take anywhere between weeks to months for results to be reported. Results are either ‘positive’ for the presence of the virus or ‘negative’ in its absence. Rapid point of care tests are available for a quick check for the virus, however these are not always very reliable, and it is best to discuss their suitability with your doctor.

Where can I get an HIV test from?

The NHS provides HIV testing for anyone who may have been exposed to the virus. These tests can be obtained through your GP or through a walk in sexual health center. Sexual health clinics are centers dedicated to providing information, support, and testing for sexually transmitted illnesses. You can also obtain HIV tests from specialist private providers of the test.

What are antibody tests?

Antibody tests are a staple method in medical practices across the world as they offer a tried and tested, highly effective method of making detecting viruses and bacteria.

These tests work by studying your body’s response to invaders. We all possess an important defensive immune system which responds to viruses and bacteria in a number of ways, one of which is the production of small molecules which work against these pathogens. These molecules are called antibodies, and form an integral part of our immune system, and a useful means by which to detect illnesses because these antibodies are completely specific to particular viruses and bacteria.

An antibody test for HIV basically involves looking for antibodies to the virus, and if these are present in sufficient quantities a positive result is given. The most commonly used antibody test for the detection of HIV (amongst many other conditions) is the ELISA, which stands for Enzyme Linked Immunosorbent Assay. This method involves the use of specially designed plates into which a blood sample is placed. This sample is then treated with a series of washes, and ultimately the test result is visible as a color change which indicates whether or not the HIV virus is present in the sample.

Who uses antibody tests?

Antibody tests are widely used in hospitals and laboratories across the world for their relative simplicity and effectiveness. The NHS makes broad use of antibody tests, not only for the detection of HIV, but for a suite of other infections and illnesses. Antibody tests are also provided by most private healthcare and private HIV test providers, again because they are the staple testing procedure used across the world.

Despite the popularity and broad usage of antibody tests, there is a growing movement towards alternative methods of HIV detection, and notable examples of these are point-of-care or rapid HIV tests, as well as nucleic acid based testing techniques. While these newer technologies are gaining more recognition and are becoming more broadly used, antibody testing remains an important part of HIV diagnosis. Rapid tests for example, still need to be confirmed via a traditional blood test.

What are the pros and cons of antibody tests?

Antibody testing is a well-established technique which has been used extensively, and so its main advantages are its reliability and effectiveness in the diagnosis of HIV.  The main disadvantage in antibody testing is something called the window period.

The window period is a length of time during which the levels of antibodies in a person’s blood is not sufficient for the accurate detection of HIV. Testing during the window period has a much higher chance of yielding a false positive or false negative, which is why a longer window period can seriously affect the reliability of a test. Antibody testing has a very variable window period ranging from a few weeks to as long as a few months (although typically the window period is at about 25 days), and considering that some people won’t be entirely sure when they were first exposed to HIV, this can be a major clinical concern.

Despite the problems posed by an unreliable window period, antibody tests have proven to be an excellent method of testing for HIV.


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