What is an EtG cutoff?
A cutoff is the concentration at or above which a laboratory or test reports EtG as positive. It is measured in nanograms per milliliter (ng/mL). A lower cutoff is more sensitive, while a higher cutoff generally reduces the likelihood that low-level incidental exposure will be reported as positive.
| Cutoff | General tradeoff | How to read it |
|---|---|---|
| 100 ng/mL | Highest sensitivity of the three | Can detect more low-level or older exposure, with more incidental-exposure concern. |
| 200 ng/mL | Middle ground | Balances some added specificity with greater sensitivity than 500 ng/mL. |
| 500 ng/mL | Higher specificity | Less sensitive to light or older drinking; commonly used to reduce incidental positives. |
Sensitivity versus specificity
Sensitivity asks, “How often does the test identify drinking when it occurred?” Specificity asks, “How often does the test stay negative when drinking did not occur?” Raising the cutoff tends to lower sensitivity and raise specificity.
In one outpatient study, the 100 ng/mL cutoff was most likely to detect heavy drinking for up to five days and any drinking during the prior two days. Cutoffs of 500 ng/mL were more likely to detect heavy drinking mainly during the prior day. These are group-level findings, not individual guarantees.
If you do not know your cutoff: do not assume. Ask the testing organization or laboratory. Our calculator defaults to 500 ng/mL only as a common comparison point.
Incidental alcohol exposure
Alcohol-containing mouthwash, hand sanitizer, foods, medications, and other products can complicate low-level EtG interpretation. This is one reason clinical context and confirmatory testing matter, especially near a low cutoff.
Source notes
See the PREVEND population analysis for sensitivity and specificity at 100 and 500 ng/mL, and McDonell et al. for cutoff performance over time. To see how a starting concentration crosses these cutoffs over time, use the EtG half-life calculator.