False positive result
What is False positive result?
A false positive result happens when a blood test shows you have a condition or infection when you actually do not. This means the test signals a problem that is not really there. False positives are uncommon, but they can occur with many types of medical tests.
These results can cause unnecessary worry and may lead to extra testing or treatments you do not need. Understanding why false positives happen helps you stay calm and work with your doctor to confirm your true health status. Most false positives are resolved with follow-up testing that provides more accurate answers.
Blood tests for infections like hepatitis, HIV, tuberculosis, and cytomegalovirus can sometimes produce false positive results. Technical issues with the test, cross-reactivity with other infections, or certain health conditions can all trigger incorrect positive readings. Getting retested or using a different type of test usually clarifies the situation.
Symptoms
- Test result showing infection or disease that you do not have
- Follow-up tests that come back negative
- No physical symptoms matching the positive test result
- Confusion or anxiety about conflicting test results
- Need for additional confirmatory testing
Many people who receive a false positive feel completely healthy because nothing is actually wrong. The only sign of a false positive is the test result itself, which does not match your clinical picture.
Concerned about False positive result? Check your levels.
Screen for 1,200+ health conditions
Causes and risk factors
False positive results can happen for several reasons. Cross-reactivity occurs when antibodies in your blood react to the test in unexpected ways. This can happen if you have another viral infection, an autoimmune disease, or have recently been vaccinated. Pregnancy can also cause false positives in some antibody tests. Technical issues in the laboratory, such as contamination or equipment problems, may produce incorrect results as well.
Certain vaccines, like the BCG vaccine for tuberculosis, can trigger positive results on TB tests even when you do not have an active infection. Recent infections with viruses other than the one being tested for may create antibodies that confuse the test. People with autoimmune conditions are at higher risk for false positives because their immune systems produce unusual antibody patterns. Understanding these factors helps you and your doctor interpret test results more accurately.
How it's diagnosed
Diagnosing a false positive requires follow-up testing to confirm whether the original result was accurate. Your doctor may order a different type of test that uses a different method to detect the same condition. For example, if an antibody test comes back positive, a more specific test like a PCR test or a Western blot may be used to verify the result. Comparing your test results with your symptoms and health history helps doctors determine if a false positive is likely.
Rite Aid offers blood testing that includes tests for hepatitis, HIV, tuberculosis, and cytomegalovirus. If you receive an unexpected positive result, retesting through our Quest Diagnostics lab network can help confirm your status. Your doctor may also recommend waiting a few weeks and testing again, as some infections take time to show up accurately in blood work.
Treatment options
- Repeat the same test after a waiting period to see if results change
- Use a different type of confirmatory test with higher specificity
- Review your medical history, symptoms, and risk factors with your doctor
- Avoid unnecessary treatments until the result is confirmed
- Consider testing at a different laboratory if technical issues are suspected
- Discuss vaccination history and recent infections that might affect results
- Seek a second opinion from a specialist if results remain unclear
Need testing for False positive result? Add it to your panel.
- Simple blood draw at your nearest lab
- Results in days, not weeks
- Share results with your doctor
Frequently asked questions
False positives happen when something in your blood reacts incorrectly with the test. Cross-reactivity from other infections, autoimmune diseases, recent vaccinations, or pregnancy can all trigger false positives. Technical problems in the lab, like contamination or equipment errors, are less common causes.
False positives are uncommon but vary depending on the specific test being used. Tests with high sensitivity may catch every true positive but also produce more false positives. More specific confirmatory tests have much lower false positive rates. Your doctor can explain the accuracy rates for your particular test.
Stay calm and talk to your doctor about follow-up testing. Do not start any treatments until the result is confirmed with a different test. Your doctor will review your symptoms, health history, and risk factors to determine the next steps. Most false positives are cleared up with a second test.
Yes, certain vaccines can trigger false positives on some blood tests. The BCG vaccine for tuberculosis can cause a positive QuantiFERON test even without active TB infection. Recent vaccinations may create antibodies that interfere with some antibody tests. Always tell your doctor about recent vaccines before testing.
Your doctor will recommend the right timing based on the specific test and your situation. Some infections require waiting 2 to 4 weeks for antibodies to develop properly. Others may be retested immediately using a different testing method. Following your doctor's guidance ensures the most accurate follow-up results.
Pregnancy can cause false positives on certain antibody tests, particularly for cytomegalovirus. Hormonal changes and immune system shifts during pregnancy may create antibody patterns that confuse some tests. If you are pregnant and receive an unexpected positive result, let your doctor know right away.
A true positive means you actually have the condition the test is looking for. A false positive means the test says you have it, but you really do not. Confirmatory testing using a different method helps distinguish between the two. True positives will remain positive on follow-up tests.
Yes, autoimmune diseases can raise your risk of false positive results on antibody tests. Your immune system produces unusual antibodies that may react with test components in unexpected ways. If you have an autoimmune condition, your doctor may choose more specific tests or interpret results more carefully.
The test result itself does not harm your physical health, but it can cause stress and worry. It may also lead to unnecessary follow-up tests or treatments if not properly investigated. Working closely with your doctor to confirm results prevents unneeded interventions and gives you peace of mind.
You cannot completely prevent false positives, but you can reduce the risk. Choose accredited laboratories like Quest Diagnostics that follow strict quality standards. Tell your doctor about all medications, vaccines, and health conditions before testing. If you receive an unexpected positive, always confirm with a second test before taking action.