Understanding a Faint Line on your Home Drug Test

Understanding a Faint Line on your Home Drug Test

How to Read a Drug Test: Is a Faint Line a Pass?


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If you have ever taken a home drug test then you know the struggle of looking at the results and wondering if you have passed. So to help you understand your results a little better we have put together this info tip sheet.

What does a faint test line indicate?

If there is any hint of a colored line next to the T (as faint as it may be), it should be considered a negative result. See examples below.


What causes a faint T-line?

Simply answered, here are some possible reasons:

  • The test was not left in the urine sample long enough may cause a faint line. 
  • Chemical imbalances or dilution of the urine sample (ie. Too much water was drank before taking the test) may cause a faint line.
  • There is not enough THC in the system to trigger a positive result, however there still may be a small trace in the urine sample may cause a faint line.
  • Low detection level test may cause a faint T-line (ie. THC 20 ng/mL test, THC 15 ng/mL, COC 150 ng/mL).
  • The expiration date of the test has past, may cause a faint line.
  • Taking a medication that is chemically similar to the drug being screened may cause a faint line.

Can we explain further?

The most common cause for a faint T-line is that there is drug present in the sample, but not enough to trigger a positive result.

The THC15 and THC20 ütest+ devices represent the highest sensitivity for antibody-based THC drug screens, meaning a faint T-line would still indicate that the drug concentration is too low for a laboratory to call positive.

The best practice is to not over-interpret a faint T-line. A faint T-line with any hint of color should always be considered a negative result.

Other reasons:

  • Something in the urine other than the drug is causing a faint test line. Drug test scientists refer to this as “matrix interference.” It could be a urine sample that has a very low or high pH level, too much protein, high levels of sediment, a low specific gravity because of the donor over-hydrates or odd color due to medication. Given the inter-person variability and the biological nature of the antibodies used to make these tests, it is impossible to guarantee that every negative urine sample will yield dark test lines. As such, it is important to refer back to point #1 above and not over-interpret a faint line. A faint test line with any hint of color should always be considered a negative result.
  • The biological materials used to make the test are weaker than usual. Sometimes, the antibody or antigen used to make the drug tests will produce lighter lines on all specimens. While this is extremely rare, lighter test lines in completely negative specimens can result from a particular antibody lot. Excellent quality control management is conducted on UTest devices to ensure the best performance, so this phenomenon is extremely rare if almost nonexistent but the same adage applies: A faint test line with any hint of color should always be considered a negative result.
  • The test is expired. The biological materials used to make these drug screens have a well-defined shelf-life. The antibody activity will decrease or become non-effective after a fixed time, so the assigned expiration date is there to prevent customers from using a test after it has expired.

Also check out our blog on how to use a home drug test and if your result is Positive, check out some detox options here or read our other blog on choosing your detox

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