False Positives in STD Testing: What You Need to Know

Q: False Positives in STD Testing: What You Need to Know

Hello： I would like to provide some suggestions for your reference. <br>Anonymous screening for sexually transmitted infections (STIs) should include HIV testing. <br>Since screening is a preliminary examination, a definitive diagnosis requires a second test using the Western blo

Infectious disease issues?

Hello Doctor, on July 6th, I had an encounter with a girl with a complicated relationship (we used a condom throughout).
Three weeks later, at the end of July, I underwent STI screening, which came back negative.
On October 9th, I went to a hospital in Taoyuan for anonymous testing, and the results showed a very faint line indicating a positive reaction.
I used another test strip, which also showed a faint line, so the doctor advised me to undergo more precise testing (I forgot the name of the test, but the result came back negative).
The doctor told me to come back for another test in three months.
I would like to ask if I need to be concerned.
Why did I get a false positive? Could it be related to the cold I had and the medication I took? I am very worried.
Thank you, Doctor.

Chen, 20~29 year old female. Ask Date: 2019/10/18

Dr. Du Shixi reply Urology

Hello: I would like to provide some suggestions for your reference.
Anonymous screening for sexually transmitted infections (STIs) should include HIV testing.
Since screening is a preliminary examination, a definitive diagnosis requires a second test using the Western blot method.
Screening alone cannot be used for diagnosis; it is intended to identify individuals who need further detailed examination.
The reason for using the ELISA method for screening is its high sensitivity, although it has lower specificity.
When conducting ELISA testing, nearly all true positive cases will be detected, but the false positive rate is also relatively high (meaning it may identify individuals who do not actually have HIV).
Therefore, confirmation through the Western blot test is still necessary.

As for why false positives occur, it is difficult to determine, and I personally believe that medications have little impact.
Online sources suggest that non-specific reactions (of unknown cause), hypergammaglobulinemia, or the presence of antibodies targeting other pathogens that resemble HIV viral antigens may lead to false positive results.
Autoimmune diseases, such as systemic lupus erythematosus, can also cause false positive results.
(If one truly wants to investigate, it may be necessary to obtain information from the screening equipment manufacturers or to look for research papers.) I would like to remind you that if you are concerned about STIs, it is important to practice safe sex at all times.
Wishing you good health.

Reply Date: 2019/10/18

More Info

Understanding false positives in STD testing is crucial for anyone who has engaged in sexual activity, especially when there are concerns about sexually transmitted infections (STIs) like HIV. Your situation highlights the complexities of STD testing, the potential for false positives, and the importance of follow-up testing.

First, let's clarify what a false positive means in the context of STD testing. A false positive occurs when a test indicates that a person has an infection when they do not. This can happen for several reasons, including the sensitivity and specificity of the test used. For example, initial screening tests like ELISA (Enzyme-Linked Immunosorbent Assay) are designed to be highly sensitive, meaning they are good at detecting true positives, but they can also yield false positives due to cross-reactivity with other antibodies or conditions.

In your case, you initially tested negative for STIs three weeks after your encounter, which is a reassuring sign. However, the subsequent test showing a faint positive line raises concerns. The faintness of the line can indicate a low level of antibodies or antigens, which may not be clinically significant. It's important to remember that many factors can influence test results, including the timing of the test in relation to potential exposure, the type of test used, and even individual biological variations.

Regarding your question about whether your cold or the medications you took could have influenced the test results, it's generally unlikely. Most common medications and mild illnesses do not typically interfere with STD test results. However, certain conditions, such as autoimmune disorders or other infections, can sometimes lead to false positives.
The recommendation from your healthcare provider to undergo more precise testing is standard practice. Confirmatory tests, such as the Western Blot or more advanced nucleic acid tests, are essential to accurately diagnose or rule out infections like HIV. These tests are more specific and can help clarify any uncertainties from initial screenings.

You mentioned that your doctor advised you to return for testing in three months. This follow-up is crucial because it allows for the window period of HIV testing to be fully accounted for. The window period is the time after exposure during which the test may not detect the infection. For HIV, this period can range from 10 days to several weeks, depending on the type of test used.
In summary, while the faint positive result can be concerning, it is essential to approach the situation with a level head. Follow your doctor's advice for further testing, and consider discussing your concerns with a healthcare professional who specializes in infectious diseases. They can provide more personalized guidance based on your specific circumstances.

In the meantime, practicing safe sex, including the use of condoms, is vital in reducing the risk of STIs. If you have any further questions or concerns, don't hesitate to reach out to your healthcare provider for support. Remember, staying informed and proactive about your sexual health is the best approach to ensuring your well-being.

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