How Accurate Are Blood Tests for HIV?

While HIV (Human Immunodeficiency Virus) doesn’t have a known cure, advancements in medical science have made it possible for today’s patients to live for years or even decades after receiving a diagnosis. However, in order for patients to have the best prognosis and exert maximum control over the progression of their illness, it is critically important to be diagnosed as early as possible. If a lab technician makes an error when testing a patient’s tissue or blood samples, leading to a missed HIV diagnosis, the patient can be deprived of years of life. In this article, our medical lab test error attorneys will explain how HIV is diagnosed, and which tests have the best accuracy rates.

How Do Doctors Test for HIV/AIDS?

There are several different methods doctors can use to test for HIV. These methods include the following:

  • CD4 Cell Count Tests – CD4 cells, more commonly known as T-cells, are a specific type of white blood cell (WBC) whose role is to fight off viruses and bacteria. HIV gradually destroys CD4 cells, progressing to AIDS once a patient’s CD4 count dips below 200. Your doctor will take a blood sample and send it to a medical lab to be tested for presence of CD4 cells.
  • HIV Antibody Tests – Antibodies are proteins created by the immune system to fight off bacteria, viruses, and other foreign bodies, which are called antigens. The first HIV antibodies to develop are usually those which fight the p24 antigen, followed by more antibodies to fight gp120 and gp41 proteins. The two most common types of HIV antibody tests are called Western Blot and ELISA. Your doctor will take an oral swab, which can return results in as little as 15 or 20 minutes. For this reason, they are sometimes called rapid tests. The FDA has approved several oral swab kits for at-home use, including OraQuick and Home Access.
  • HIV Combination Tests – Combination tests detect both antibodies and the antigens they fight against. The advantage of using a combination test is that it can detect the virus up to 20 days earlier than an antibody test. Your doctor will take a blood sample and send it to a lab for screening. Combination tests are also called fourth generation tests.
  • HIV RNA Tests/Nucleic Acid (NAT) Tests – RNA stands for ribonucleic acid. Unlike antibody tests, RNA tests screen for the virus itself, which is detectable in blood before antibodies start to develop. Your doctor will take a blood sample to send to a lab for screening.

Additionally, patients should undergo viral load testing immediately after being diagnosed with HIV, and again every two to eight weeks during the initial stages of treatment. Once the patient finds a good treatment regimen, viral load testing frequency can be reduced to every three to six months, as directed by your physician. A viral load test is a blood test which measures how much of the virus is present in the bloodstream. Patients with low viral loads generally have a better prognosis than those with high viral loads.

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How Often is HIV Misdiagnosed, and Which Test Types Are Most Accurate?

Generally speaking, HIV tests have high accuracy rates. However, while statistically rare, potential still exists for tests to come back with false negatives (testing negative when a patient has HIV) or false positives (testing positive when a patient does not have HIV). Various HIV test accuracy statistics are listed below.

  • The website of OraQuick, a rapid in-home test which calls for an oral swab, claims that “in studies, the OraQuick oral fluid test detected 91.7% of people who were infected with HIV, and 99.9% of people who were not infected with HIV.” In other words, OraQuick failed to detect HIV in about 8.3% of HIV positive patients, or about eight out of every 100 users.
  • According to the AIDS Action Committee (AAC), Western Blot tests, which are used to help confirm the results of positive ELISA tests, have an approximate accuracy rate of 99.5%. Quest Diagnostics also notes that Western Blot tests “may not accurately reflect infection status during acute infection.”
  • According to the National AIDS Manual (NAM) AIDSmap, which has been a trusted source of HIV/AIDS information since the 1980s, an evaluation by the UK’s now-defunct Health Protection Agency (later replaced by Public Health England) found that nine out of 10 fourth generation HIV tests had an accuracy rate of 100%. However, one combination test (Abbott Murex Ag/Ab) failed to diagnose HIV in one out of 508 samples. That test was found to have an accuracy rate of 99.8% – still high, but not perfect.
  • NAM AIDSmap also reports that “false positive results are fairly common” in HIV RNA tests, adding that “most tests only detect HIV-1,” and that “very few are capable of detecting HIV-2.” HIV-1 and HIV-2 are two different viruses. Most cases of HIV in the United States involve HIV-1, with HIV-2 primarily concentrated in West African countries such as Cameroon and Gabon.

To help reduce the risk of receiving an inaccurate diagnosis, all patients are strongly advised to undergo follow-up testing to confirm any initial test results. If you have any questions about how to interpret at-home test results, you should consult with a physician right away.

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If you found out you were HIV positive after a lab mix-up caused a misdiagnosis or false negative, or if you received a false positive due to a careless lab technician’s mistake, you may be able to recover compensation to help pay for your medical bills and other expenses. To learn more about your legal options in a free and completely confidential legal consultation, call the Baltimore clinical malpractice lawyers of Whitney, LLP at (410) 583-8000.


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