From time to time we receive questions from customers who notice faint or unclear line on their STI rapid test results. This article explains what those faint lines might mean and the best next steps.
Understanding the result lines
Your STI rapid test comes with an instruction card showing how to read the lines for each parameter tested.
Additionally, it’s vital to interpret test results within the time frame specified in the instruction card of your STI rapid test. Reading results early or later than the recommended time can lead to inaccurate conclusions.
This card is included in these tests: STI 8in1, STI 3in1, STI 2in1, Chlamydia urine test.
Testing for infections like Syphilis may involve considering the window period, which is the time between exposure and when the infection becomes detectable through testing. Negative results in this period may not be conclusive.
One clear control line (C) and no test line (T); Negative
One control line (C) and a clear test line (T); Positive
One control line (C) and a faint test line (T); Borderline / unclear result
No visible line in the Control region (C), regardless of Test region (T); Invalid result (indicates a testing error or insufficient specimen).
Why faint lines happen
In some cases, a very faint line may appear in the test area. Any visible line in the Test region (T), regardless of intensity, should be interpreted with caution. Follow the manufacturer’s guidelines regarding the opacity and intensity of the lines, as these are significant indicators when interpreting unclear results. This is particularly important when symptoms or risk factors are present.
A faint line can occur for several reasons:
The test is detecting a very low level of the target bacteria or virus
The infection is in an early stage and may not yet show a clear result
The incubation period for the STI has not yet passed
Slight variations in how the sample flowed through the test strip- Antibody levels are insufficient or fluctuating close to the detection threshold.
What to do if you see a faint line
If you see a faint or borderline line, we recommend:
Repeat the test in 1–2 weeks This allows time for the infection (if present) to develop to a level detectable with more certainty. Incubation periods differ between STIs, so retesting can provide a clearer answer. - For infections like Syphilis, retest at 12 weeks after potential exposure to ensure accuracy due to the window period for developing detectable antibodies.
Consider a laboratory test A lab test offers higher sensitivity and can confirm whether the faint line indicates a true positive result.
Follow up if the line becomes more visible If you repeat the test and the line is clearer or more defined, this could indicate a positive result. In this case, you should follow up with a lab test immediately.
We offer a lab test which analysis for Chlamydia, Gonorrhea and Syphilis. But if you test positive, we cannot provide medication if needed.
If you test positive
If a rapid or lab test confirms an STI:
Contact a healthcare provider for appropriate treatment.
For bacterial STIs (such as chlamydia or gonorrhoea), treatment usually involves antibiotics prescribed by a doctor.
Avoid sexual contact until you have completed treatment and have been retested if recommended by your doctor.
False positive
As with all STI rapid tests, there is a risk of a false positive. A test may show a positive indication even when the result is negative for a few reasons. These are the three most common:
Cross-reactivity: The test may react to something in your sample that’s chemically similar to the target pathogen, but not actually the pathogen itself.
User handling or reading errors: Misinterpreting faint lines, incorrect timing, or contamination can lead to inaccurate results.
Immune system variability: For antibody-based tests, your immune response might cause a signal even if there's no active infection - for example, due to a past infection or even another condition. This test is a immunochromatographic technology test which shortly speaking means it's an antibody-based test.
Reading test results using chatbot
You can get help interpreting your STI rapid test results by uploading a clear image of the cassette to the chatbot.
Before uploading an image, please make sure that:
✅The cassette is placed vertically.
✅The cassette is placed on a flat surface, preferably white or black, with no other objects or tests in the background. Do not hold the cassette in your hand or in the air.
✅The image is of good quality, and not distorted.
✅The lighting is good.
✅ Picture is taken at the time that the test should be read, not earlier or later.
