A false-positive result is when a person not infected with a virus or a disease receives a positive test result. A person tested for HIV may get a false-positive result due to errors in home tests, the presence of other health conditions, and facility or provider-based issues.

In 2019, the Centers for Disease Control and Prevention (CDC) estimated that 1.2 million people in the United States have HIV, and close to 160,000 are unaware they have the condition. The CDC also reports that less than 40% of people in the U.S. have ever had an HIV test.

False-positive HIV test results can have a significant emotional and social impact on a person. However, if an initial test turns out to be positive, a person will likely undergo additional testing to determine the test’s accuracy.

Continue reading to learn more about the common causes for receiving false-positive HIV test results.

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The most common causes of an incorrect HIV test result include the timing of testing, type of HIV test used, other health conditions, technical issues at the testing site, or a faulty HIV test.

Timing of testing

After a person contracts HIV, the body does not immediately produce antibodies to fight off the infection.

This is why HIV tests have a window period, the period between the person contracting HIV and the time a test can detect its presence in the body.

Testing too early, before the window period, can result in a false-negative result.

Type of HIV test used

Most testing sites use HIV antibody tests, called ELISA tests, for rapid screening of HIV. These tests detect antibodies that the body creates in response to an HIV infection.

However, many people also do rapid HIV testing using oral fluid and finger-prick tests. A 2017 study found that many children undergoing longstanding antiretroviral therapy (ART) received false-negative results from oral fluid tests.

Moreover, a 2018 review found that while self-testers often get reliable and accurate results, incorrect specimen collection is the most common error that affects the performance of these tests.

The same review mentioned that blood-based tests are more specific and reliable than oral fluid rapid tests. Despite this, many people prefer oral fluid tests for their convenience.

Read more about ELISA tests here.

Other health conditions

The most common cause of a false-positive HIV result is when the test detects antibodies for a different infection or substance. For example, recent viral infections may cause a false-positive ELISA test result.

A 2020 study reported false-positive HIV results due to a schistosomiasis infection. In a 2018 case study, a person with babesiosis had a false-positive HIV test, which became negative after successful treatment.

Certain other conditions that may cause a person to have a false-positive in an ELISA include:

The following may also cause a false-positive result:

Test inaccuracy

HIV tests are generally highly accurate but may produce a small number of false-positive results. The CDC states that HIV tests have 99.6% specificity. This means that for every 1,000 people without HIV who take the test, 996 will receive true negative results, and four may receive a false positive. However, newer tests have a lower chance of causing false positives.

Technical or clerical error

Mishandling samples, mislabeling, and mixing up specimens can occur during testing. At-home tests may also be prone to user error. Some testing devices may rely on subjective interpretation when reading a result, leading to incorrect interpretations when results are borderline.

Of the 1.2 million people who have HIV in the U.S., around 13% do not know they have HIV and need to receive a screening for the condition. Moreover, about 40% of new HIV transmissions are from people who do not know that they have HIV.

The risk of HIV transmission depends on the behavior or exposure. The CDC measures a specific behavior’s likelihood to transmit HIV for every 10,000 exposures.

Blood transfusion has the highest risk of transmitting HIV. Receptive anal sex, or receiving the penis into the anus, also increases transmission risk. A 2010 meta-analysis found a 1.4% risk of transmission, or 1 in every 71 exposures, from unprotected anal sex, regardless of whether the receptive person is male or female.

Needle sharing also carries some risk. A person has a 1 in 160 chance of getting HIV when they share a needle with a person with the condition.

Impact on testing

The prevalence of HIV, or how common it is in a community, can affect the chances of getting a false-positive result. In communities where HIV is common, the probability that a positive result is accurate is higher. In contrast, in places where very few people get HIV, getting true-positive results is rarer.

If a person receives a positive result in a screening test, they will likely undergo additional testing to confirm the result. A specialist can administer several kinds of confirmatory tests for various reasons, including:

  • to detect antibodies more effectively than regular screening tests
  • to detect viral load in the blood
  • to check if the person has HIV-1 or HIV-2

According to the CDC fact sheet on false-positive HIV results, if a person had a screening through a laboratory, the lab will likely use the same specimen to perform additional tests.

However, if the positive result is from a rapid test or a self-test, follow-up tests can involve:

  • forwarding the person’s specimen to a laboratory
  • doing a rapid test algorithm
  • referring a person to a healthcare professional for a follow-up test

Finding the cause of a false-positive result

Since there are various reasons for false-positive results, individuals should speak with a doctor about the probable cause. Some may be due to human error, such as a technical or clerical oversight.

However, a false-positive result can also result from another condition, such as an STI or an autoimmune disorder. Autoimmune disorders that may cause false-positive results include lupus and rheumatoid arthritis.

HIV tests cannot detect whether a person has the virus immediately after exposure. This is because there is a window period before a test can detect the presence of HIV in the blood. If a person tests during this time, they will likely receive a negative result.

The CDC recommends that a person retest 45 days after exposure and an initial negative result from a laboratory-based antibody or antigen test and 90 days after exposure for all other tests.

The CDC recommends everyone between 13–64 years old undergo HIV screening at least once in their lives as part of their routine health care. Early diagnosis of HIV allows people to have longer, healthier lives and reduces the likelihood of transmission.

Additionally, the CDC recommends individuals at higher risk get tested at least once a year. These include:

  • men who have sex with men
  • transgender individuals
  • injection drug users (IDUs)
  • African Americans
  • Latinx people

Aside from those mentioned above, hiv.gov recommends the following people to get tested often:

  • people who have had sex with an HIV-positive person
  • people who have had more than one sexual partner
  • people engaged in sex work, or those who exchange sex for money or drugs
  • people diagnosed with or receiving treatment for another STI
  • people who have had sex with someone who has experienced any of the above
  • people who have a sexual partner whose sexual history is unknown

There is currently no cure for HIV. However, people who test positive for HIV should immediately start ART. ART is an effective treatment that manages the virus. It reduces a person’s viral load to very low levels. When levels reach a point that standard tests may not detect, this is known as undetectable HIV.

A person at risk of contracting HIV should get screened for HIV and other STIs. Several practices may also help people avoid contracting the disease, including:

  • abstaining from sexual intercourse and activities
  • not sharing needles
  • avoiding having multiple sexual partners
  • using a condom or another barrier method during sexual activities
  • staying in a monogamous relationship

A person at risk for HIV, including people with HIV-positive partners and IDUs, can take pre-exposure prophylaxis to prevent getting the disease. In the same way, those who suspect possible exposure to HIV should speak with their healthcare providers about taking post-exposure prophylaxis.

While uncommon, a person who does not have HIV may receive a false-positive result. However, HIV is not diagnosed with a single test and requires confirmatory tests to confirm the accuracy of the initial test.

Certain factors can cause a false-positive HIV test, including other health conditions and human and technical error.

A person at risk of contracting HIV can take preventive measures to avoid getting the virus. Someone who turns out to have a true-positive test result can receive HIV treatment to control the condition and go on to lead a long, healthy life.