What tests are used for HIV diagnosis?
Testing will require blood or other bodily fluid samples for laboratory analysis. Several types of tests are available, many of which are able to detect an infection almost right away. That said, an infection can only show up within 6 months following contraction even if testing has occurred during the period of time before, as the body takes time to produce antibodies. The white blood cells in the body typically increase, producing antibodies, when there is the presence of any infection. The increase in production of these cells can sometimes take a little time to happen following exposure to infection.
When it comes to an HIV infection, the sooner you are tested and diagnosed the better. Tests available for making a diagnosis are:
- Antibody screening tests (immunoassay or ELISA tests): This testing methods checks for the production of protein (antibodies) that the body will naturally produce in response to the presence of an infection. This test is ideally done between 2 and 8 weeks following exposure. Early infections are not usually determined with this screening test, but are fairly accurate for diagnosis. To perform this test, a medical professional (doctor) will take a small sample of blood for assessment in the laboratory. A doctor can also use samples of urine or fluids, other than saliva, taken from the mouth. Blood samples are preferred as more antibodies can be found in the blood compared to other fluids. There are rapid versions of this test available which can be made available within 30 minutes if necessary. Rapid tests have been known to give false negative results, however.
- Antigen / antibody combination tests: This screening test also uses a blood sample and can detect an HIV infection up to 20 days earlier than an antibody screening test. In the laboratory, a technician will assess a blood sample for the HIV antigen (known as p24), which is a protein that forms part of the virus. This protein is usually present within 2 to 4 weeks following exposure to the infection. A technician will also check for HIV antibodies. Rapid tests are also available for this screening option and can be ready within 20 minutes.
- RNA test: This screening method can detect the HIV virus itself within 10 days after exposure. This test will be favoured if a person falls in a high-risk group or displays obvious initial stage symptoms. The test is expensive and thus isn’t usually the first test performed for diagnosis.
- FDA-approved in-home test kits: In the USA, approved home screening kits are available for private testing use. The kits require a person to take their own blood (through pricking a finger) or oral samples (a swab of mouth fluids) and send these to a laboratory for analysis. Results are usually available within a few business days. Oral fluid results may take a little longer. If preferred, this process can be handled anonymously. If results are positive, however, a follow-up test will be recommended. In most cases, it is best to seek medical assistance for screening as these can be done safely, and in some cases anonymously as well.
Follow-up testing for positive results
If traces of HIV are found in screening samples, a positive result will be given. All rapid tests which have positive results will be followed up with a standard laboratory test to confirm a diagnosis and ensure there are no false negative results. Positive results from a standard laboratory test will undergo more detailed testing using the same blood sample as well.
These detailed screenings will involve:
- Antibody differentiation between infection strains (HIV-1 or HIV-2)
- An indirect immunofluorescence assay (Western blot)
- An HIV-1 nucleic acid test
- An RNA test
Results obtained within 3 months following exposure may be followed up with repeat testing at the 6-month mark. Antibody production is best observed at this time and produces the most accurate result, particularly if an HIV infection is present in the body.
Tests required to monitor an HIV infection
If a result is positive for HIV, doctors will highly recommend follow-up testing to monitor the nature of the infection on an on-going basis. Common tests for monitoring purposes include:
- Monitoring CD4 count: A healthy individual usually has a CD4 count of well over 500 white blood cells per cubic millimetre. An HIV infection targets these cells and progressively destroys them as the disease advances through its stages. Doctors use ongoing tests to measure CD4 counts as a means to stay abreast of the disease progression. Once this count drops below 200 cells per cubic millimetre, the disease is effectively in its most advanced state and an AIDS diagnosis will be made. With treatment, doctors can slow down the progression, levelling out or increasing the CD4 count and many HIV positive individuals never reach the most advanced stage of their disease. Monitoring CD4 counts is also a valuable indicator for a doctor as to whether treatment is working and can give a fairly accurate overall assessment of a person’s immune function as a whole. Where CD4 counts drop, a doctor may recommend various medications as preventative measures for other possible infections which will lead to period of illness. CD4 counts may be tested every 3 to 6 months.
- Monitoring viral load: The amount of virus in the bloodstream varies from person to person. Doctors will also wish to assess this amount on an ongoing basis. A load that is low will not typically affect a person’s overall health too negatively in terms of symptoms. A low load also means that the virus is more difficult to spread (but this is not impossible). A doctor will constantly measure viral load as another means to monitor the effectiveness of treatment, as well as the stage status of the disease. As well as working to prevent lowered CD4 counts, treatment is also designed to reduce viral load in an effort to curb advancement to the final stage of the disease. Viral load screenings will likely be recommended every 3 to 4 months.
- Monitoring HIV strains and medication resistance: If at any stage, it is suspected that a person’s strain of HIV is possibly resistant to any medications used during treatment, tests may be ordered to check or confirm this. Resistance can hamper the progress of treatment and medication options may need to be adjusted to prevent this.
- Tests (as required) for complication management: Side-effects and various health complications are common for those living with HIV. During check-ups doctors may perform various other tests to assess a person’s liver and kidney function, as well as a check for any changes to metabolic or cardiovascular functions too. HIV is capable of changing or mutating in the body which can have adverse effects on the body, bringing with it a variety of other health concerns. Other tests a doctor is likely to recommend would be to check for the presence of other infections which can lead to other ailments and complications. These include checks for other STIs (such as gonorrhoea, herpes, chlamydia and syphilis), tuberculosis, toxoplasmosis and urinary tract infections. Regular blood samples may be recommended to test for anaemia and assess blood sugar levels. A doctor will also test triglyceride and cholesterol levels regularly as both the virus and ART medications can contribute to raised levels.
All positive HIV infections should be carefully monitored by healthcare professionals on an ongoing basis. The disease cannot yet be cured, but it can be reasonable controlled with careful treatment practices. Any changes to a person’s physical state must be discussed with a doctor and is likely to occur from time to time. An HIV positive person has a compromised immune system for life and will experience symptoms of other illnesses periodically. Doctors will be able to better manage a person’s overall health when in the know about new or recurring symptoms which could indicate new infections or serve as an indication that treatment is no longer effective.