Human papillomavirus (HPV) is one of the most common sexually transmitted infections, with an estimated 80% of sexually active individuals contracting the virus at some point in their lives. HPV testing is commonly used to screen for cervical cancer in women, since certain high-risk strains of HPV can cause abnormal cell changes that may lead to cancer if left untreated. However, like any screening test, HPV testing is not 100% accurate and false positive results can occur.
What is a false positive HPV test result?
A false positive HPV test result means that the test detected HPV but the person does not actually have an active HPV infection. There are a few reasons why this can happen:
- The test picked up a very low level of HPV that the body cleared on its own before the test was performed
- The test mistakenly detected another type of virus or cell irregularity as HPV
- There was a technical error in how the sample was collected or tested
A false positive does not mean the test gave an incorrect strain result. If the test detects any strain of HPV, even if it’s a strain that is not high-risk, it will read as a positive result overall. The strain typing can still be accurate even if the overall positive result is false.
How common are false positive HPV test results?
Estimates vary on how often false positives occur for HPV testing. According to a review published in The Lancet, the false positive rate is typically reported to be between 2% and 5%. However, a few key factors influence false positive rates:
- Population tested – False positive rates are higher in populations with low rates of HPV infection overall. In populations with a high prevalence of HPV, false positives are less common.
- Age – HPV false positives are more common in older age groups where HPV infection is less prevalent. The false positive rate is lower in younger sexually active women.
- Type of test – Some types of HPV tests are more prone to false positives than others. Tests that detect HPV DNA are more specific than those that detect HPV RNA.
Research has found false positive rates varying from less than 2% up to 8% depending on the factors above. But overall, a typical range is 2-5% across broader study populations.
How are false positives minimized on HPV testing?
Although false positives can occur, HPV testing is still considered an accurate cervical cancer screening method when performed correctly. There are some techniques to help minimize false positives:
- Use HPV DNA tests rather than RNA detection tests which are less specific
- Do not use HPV testing in populations under age 30 where HPV is highly prevalent
- Repeat testing to rule out transient HPV infections – two positives indicates a true result
- Perform HPV genotyping to identify high-risk strains if the overall test is positive
- Use liquid-based cytology samples rather than tissue samples to reduce errors
- Have strict protocols in place for sample collection, handling, and testing procedures
Following best practice guidelines for HPV testing is the best way for clinicians to reduce the chances of false positive results.
What happens if you get a false positive HPV test result?
If your HPV test comes back positive but you do not actually have HPV, your doctor will usually recommend follow-up testing to confirm:
- Repeat the HPV test – If this is also positive, it likely represents a true infection
- HPV genotyping test – This looks for high-risk HPV strains
- Cervical cytology – Looks for abnormal cervical cells under the microscope
- Colposcopy – Visual examination of the cervix after applying a diluted vinegar solution
- Cervical biopsy – Removal of a small sample of cervical tissue to test for abnormalities
In most cases, repeat testing will come back negative if the original positive was a false positive. If abnormal cells are detected, you will require treatment and monitoring. But if further testing is normal, you can be reassured the initial result was incorrect and you do not have HPV.
Conclusion
HPV testing is an invaluable cervical cancer screening tool, but false positives do occur in a small percentage of results. By understanding what causes false positives and using proper testing protocols, healthcare providers can minimize inaccurate results. If you receive an unexpected positive HPV test, do not panic – follow up testing will determine if this was a false positive or true positive requiring further management.
Frequently Asked Questions
What is the false positive rate for HPV testing?
Most studies estimate the false positive rate for HPV testing to be between 2-5%. However, false positive rates can vary across different populations and test methods. False positives are more common with less accurate HPV RNA tests, in older age groups, and in populations with low HPV prevalence.
Why do false positive HPV results happen?
There are a few reasons a false positive HPV result can occur:
- A very low level of transient HPV was detected that cleared spontaneously
- Another type of virus or cell irregularity was mistaken for HPV
- An error occurred in sample collection, handling, or testing procedures
Even though HPV tests are generally accurate, no test is 100% perfect at distinguishing between HPV and other closely related viruses or cell abnormalities.
Can you get a false positive on one HPV strain but still have another strain?
Yes, it is possible to get a false positive result on one HPV strain but still test positive for another strain. HPV genotyping looks for 13-14 individual high-risk HPV types. You could test falsely positive for one strain but actually have a true infection with a different high-risk strain. The overall positive result would still be accurate even if the specific strain typed incorrectly.
How many false positives occur from repeat HPV testing?
Repeat testing after an initial positive HPV result greatly reduces the chances of a false positive diagnosis. Studies have found that over 90% of persistent double-positive HPV test results represent a true underlying HPV infection. The false positive rate drops to 1% or less when HPV testing is repeated and confirm as positive. This demonstrates the value of verifying an initial positive result with follow-up HPV testing.
Should you get tested for HPV again after a positive result?
Yes, repeat HPV testing is recommended if you have an initial positive result. Testing again in 6-12 months can help confirm whether the initial positive was false or indicative of an actual HPV infection needing further evaluation. Two positive HPV tests makes it highly likely you have a true positive. Repeat testing provides added certainty.
What else can be done to confirm an HPV test result?
In addition to repeat HPV testing, other follow-up tests that may be used to confirm an initial positive HPV result include:
- HPV genotyping to identify high-risk strains
- Cervical cytology (Pap smear) to look for abnormal cells
- Colposcopy visual inspection of the cervix
- Cervical biopsy to take a tissue sample
If multiple tests come back normal, the original positive HPV result was likely false. If abnormalities are detected, it confirms a true positive.
Key Takeaways
The main points about false positive HPV test results include:
- False positives occur in an estimated 2-5% of HPV test results
- False positives are more common in certain populations and with less accurate test methods
- A false positive means HPV was detected but no actual infection exists
- Repeat testing helps confirm or rule out a false positive result
- Follow-up HPV genotyping and cervical cytology also help validate true test results
- While false positives are possible, HPV testing remains an important cervical cancer screening tool when done properly