What are the tests for HIV/AIDS?
HIV/AIDS diagnosis, monitoring and therapy have come a long way from the days when a diagnosis was a death sentence. Crucial parts of the effective treatment regimens developed in the last 40 years are consistent monitoring of the viral load (the amount of virus in the blood), and the immune cell count, which function as biological markers of the disease’s progression.
The sexually-transmitted human immunodeficiency virus hijacks your cells to produce more of itself. Left unchecked, the virus overwhelms your immune system, making it less effective and bringing it closer to collapse. This progression of the disease leads to AIDS, or acquired immune deficiency syndrome. (So, all people with AIDS have an HIV infection, but not all people with HIV infection have AIDS).
Treatment with anti-viral therapy has vastly improved since the global HIV/AIDS epidemic first started. Many with an HIV diagnosis can now live long and productive lives relatively free of serious symptoms. Still, no one has figured out a cure for HIV, and people who have it need to have some kind of antiviral therapy for the rest of their lives.
Testing of the blood and saliva from the initial diagnosis and throughout the patient’s life is important. Knowing if you have HIV is crucial so that treatments can begin to protect your immune system and to protect your sexual partners. It is also important for your doctors to order periodic screening to monitor your immune cell count and your viral load to tell how you are responding to treatment.
These tests also show your treatment team whether the specific viruses in your body have developed an immunity to your drug regimen, alerting your doctor that it’s time to change up your treatment plan.
What are the tests to diagnose HIV?
In 1985, a blood test became available that measures antibodies to HIV that are the body's immune response to the HIV. The test that for decades had been most commonly used for diagnosing infection with HIV was referred to as an ELISA. If the ELISA found HIV antibodies, the results needed to be confirmed, typically by a test called a Western blot.
Newer tests look for these same antibodies in saliva. Some provide results within one to 20 minutes of testing. As a result, the FDA has approved home HIV antibody testing that is self-administered using saliva. Antibodies to HIV typically develop within several weeks of infection. During this interval, patients have virus in their body but will test negative by the standard antibody test, the so-called "window period.
In this setting, the diagnosis can be made if a test is used that actually detects the presence of virus in the blood rather than the antibodies, such as tests for HIV RNA or p24 antigen. Several tests are now approved that measure both HIV antibodies and p24 antigen, shrinking the duration of that early window period in which the infection is difficult to detect. In fact, federal guidelines currently recommend that HIV screening tests be performed with these assays and, if they are positive, that a confirmatory antibody test be performed that will determine if the patient has HIV-1, the most common form of HIV circulating around the world, or HIV-2, a related virus that occurs most frequently in Western Africa. If the confirmatory antibody test is negative, then there remains the possibility that the original test detected viral p24 antigen and not antibodies, and therefore infection still is likely. Therefore, the recommendations are that if the confirmatory antibody test is negative a test for HIV RNA test for the presence of virus, should be performed. If the antibody is negative and the viral test is positive, the patient is diagnosed with acute or primary HIV infection and will develop a positive antibody test over the ensuing weeks.
Although the tests for detecting HIV infection continue to improve, they still require people to volunteer for testing. It is estimated that approximately 15% of those infected with HIV in the United States are unaware of their infection because they have never been tested. In order to decrease the number that are unaware of their HIV infection status, in 2006, the Centers for Disease Control and Prevention recommended that all people between 13 and 64 years of age be provided HIV testing whenever they encounter the health care system for any reason. In addition, resources are available to facilitate people finding local HIV testing centers (https://gettested.cdc.gov/).
What tests do doctors use to monitor HIV?
Two blood tests are routinely used to monitor HIV-infected people. One of these tests, which counts the number of CD4 cells, assesses the status of the immune system. The other test, which determines the so-called viral load, directly measures the amount of virus in the blood.
A severe reduction in a type of cell in the blood (CD4 cells) marks the progression from HIV into full-blown AIDS. Your CD4 cells compose an important part of the immune system. These cells, often referred to as T cells, help the body fight infections.
In individuals not infected with HIV, the CD4 count in the blood is normally above 400 cells per mm3 of blood. People generally do not become at risk for HIV-specific complications until their CD4 cells are fewer than 200 cells per mm3. At this level of CD4 cells, the immune system does not function adequately and is considered severely suppressed. A declining number of CD4 cells means that HIV disease is advancing. Thus, a low CD4 cell count signals that the person is at risk for one of the many opportunistic infections that occur in individuals who are immunosuppressed. In addition, the actual CD4 cell count indicates which specific therapies should be initiated to prevent those infections.
The viral load actually measures the amount of virus in the blood and may partially predict whether or not the CD4 cells will decline in the coming months. In other words, those people with high viral loads are more likely to experience a decline in CD4 cells and progression of disease than those with lower viral loads.
In addition, the viral load is a vital tool for monitoring the effectiveness of new therapies and determining when drugs are and are not working. Thus, the viral load will decrease within weeks of initiating an effective antiviral regimen. If a combination of drugs is very potent, the number of HIV copies in the blood will decrease by as much as hundredfold, such as from 100,000 to 1,000 copies per mL of blood in the first two weeks and gradually decrease even further during the ensuing 12-24 weeks.
The ultimate goal is to get viral loads to below the limits of detection by standard assays, usually less than 20 to 50 copies per mL of blood. When viral loads are reduced to these low levels, it is believed that the viral suppression will persist for many years as long as the patient consistently takes their medications.
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What is drug resistance testing?
Drug-resistance testing also has become a key tool in the management of HIV-infected individuals. Resistance testing is now routinely used in individuals experiencing poor responses to HIV therapy or treatment failure.
In general, a poor response to initial treatment would include individuals who fail to experience a decline in viral load of approximately hundredfold in the first weeks, have a viral load of greater than 500 copies per mL by week 12, or have levels greater than 50 copies per mL by week 24. Treatment failure would generally be defined as an increase in viral load after an initial decline in a person who is believed to be consistently taking his or her medications.
Because drug-resistant viruses can be transmitted, guidelines from the U.S. Department of Health and Human Services (DHHS) (https://aidsinfo.nih.gov/) and International Antiviral Society-USA (IAS-USA) have suggested that resistance testing be performed in individuals who have never been on therapy to determine if they might have acquired HIV that is resistant to drugs.
The goals of antiviral therapy are to enhance immunity and delay or prevent clinical advancement to symptomatic disease without inducing important side effects or selecting for drug-resistant virus. Currently, the best marker of a drug's activity is a decrease in the viral load.
Ideally, prior to initiating treatment, the viral load and the CD4 cell count should be checked and the viral load test then repeated after approximately four weeks of treatment. If the patient is beginning a regimen that includes two to three drugs for which the patient's virus does not appear to be resistant, it is expected that the amount of virus should decrease by at least a hundredfold during this interval.
The ultimate goal is for the viral load to decrease to undetectable levels which should occur by approximately 12-24 weeks. There are some individuals that despite taking all of their medications correctly will suppress their viral load to less than 200 copies/mL but not consistently undetectable levels. It is not completely known how to optimally manage this situation but many experts would continue to monitor on current therapy as long as viral load remains below 200 copies/mL.
Those who are not having an appropriate response to therapy need to be questioned to make sure that they are taking their medications correctly, and if not, why. If the viral load is not going to undetectable levels and the patient is taking the medications correctly, then it is likely that there is a resistant virus to some of the medications. Drug-resistance testing then should be performed and the patient managed as described in the next section.
Once the patient's viral load is suppressed, they can often have viral load and CD4 cell counts performed less frequently (for example, every three to four months and in select cases every six months or possibly even less).
There are currently two main types of resistance tests available in the clinic: one that is called a genotype and the other a phenotype assay. The former looks for mutations in the virus and the latter the actual amount of drug it takes to block infection by the patient's virus.
The genotype test is very helpful in those being screened for the presence of resistant virus prior to initiating treatment and those experiencing viral rebound on one of their first treatment regimens. The phenotype test is particularly useful in those who are highly treatment experienced and have substantial amounts of drug resistance, especially to the protease class. The information derived from these tests, along with a tropism test will ultimately tell the provider which of the many approved drugs are likely to be fully active against the specific patient's virus.
Using this information, the goal is to include at least two and at times preferably three fully active drugs in the next regimen in order to optimize the chances of suppressing the viral load to undetectable levels. It is often useful to seek expert consultation in managing those with multidrug resistant virus.
What happens if the viral load increases while on HIV therapy?
If the patient does suppress their virus to undetectable levels on antiviral therapy but then develops detectable virus, several things should be considered. First, it must be established that the patient is taking the medications correctly. If they are missing doses, then every effort must be made to understand why this is happening and correct the situation, if possible.
If poor adherence is a result of drug side effects, efforts should be directed toward managing the side effects or changing to a better-tolerated regimen. If poor adherence is occurring because of the medication schedule of dosing, new strategies should be discussed such as placing medications in a pillbox, associating the dosing with certain daily activities such as tooth brushing, or possibly changing the regimen. Finally, if the reason for poor adherence is depression, substance abuse, or another personal issue, these issues need to be addressed and managed.
It is important to remember that sometimes, for reasons not entirely understood, the viral load can briefly increase. Unexpected increases, therefore, require repeated testing of the viral load before any clinical decisions are made. If, however, the viral load is continually detected despite proper adherence to the prescribed therapy, serious consideration must be given to the possibility that the virus has become resistant to one or more of the medications being given, especially if viral load is greater than 200 copies/mL.
There is now an abundance of data showing that the use of drug-resistance tests can improve the response to a follow-up regimen. Testing can be used to determine if an individual's HIV has become resistant to one or more of the prescribed drugs.
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DHHS Panel on Antiretroviral Guidelines for Adults and Adolescents. "Guidelines for the Use of Antiretroviral Agents in HIV-1 Infected Adults and Adolescents." Washington D.C.: Department of Health and Human Services, 2018. <https://aidsinfo.nih.gov/contentfiles/lvguidelines/adultandadolescentgl.pdf>
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