Alcohol test results are reported in different units depending on the type of test, and each one uses its own scale and cutoff values. A breathalyzer gives you a BAC percentage, a urine test measures a metabolite in nanograms per milliliter, and a hair test uses picograms per milligram. Knowing which test you’re looking at is the first step to understanding what your number actually means.
Breathalyzer and Blood BAC Results
Breathalyzer and standard blood alcohol tests both report results as blood alcohol concentration, or BAC, expressed as a percentage. A BAC of 0.08% means there are 80 milligrams of alcohol per deciliter of blood. If your results come back in mg/dL instead of a percentage, divide by 1,000: 80 mg/dL equals 0.08%.
Here’s what different BAC ranges generally indicate:
- 0.00%: No alcohol detected.
- 0.01% to 0.05%: Mild effects. You may feel relaxed and slightly less alert, with minor changes in judgment.
- 0.06% to 0.15%: Noticeable impairment. Slurred speech, reduced coordination, and impaired judgment, memory, or balance are common in this range.
- 0.16% to 0.30%: Severe impairment. Risk of blackouts, vomiting, and significant loss of motor control increases sharply.
- Above 0.30%: Life-threatening range. Loss of consciousness, suppressed breathing, and alcohol poisoning become serious concerns.
The legal driving limit in most U.S. states is 0.08%. Some states also penalize drivers at lower levels. New York, for example, considers a BAC above 0.05% legal evidence of impairment, and a BAC of 0.18% or higher qualifies as aggravated DWI. Commercial drivers face stricter standards, typically 0.04%. For drivers under 21, most states enforce a zero-tolerance policy at 0.02% or lower.
How Fast BAC Drops
Your body clears alcohol at a relatively fixed rate, but that rate varies by person. Non-drinkers metabolize alcohol at roughly 12 mg% per hour, which translates to a BAC drop of about 0.012% each hour. Social drinkers clear it a bit faster, around 0.015% per hour. People with heavy, long-term drinking histories can metabolize alcohol nearly twice as fast, at roughly 0.030% per hour, because the liver adapts to sustained exposure.
This means if you’re a moderate drinker who blows a 0.08%, it will take roughly five to six hours for your BAC to return to zero. Body weight, biological sex, food intake, and liver health all influence the exact timeline. Women generally reach higher BAC levels than men after the same number of drinks due to differences in body water content and enzyme activity.
Urine EtG Test Results
EtG (ethyl glucuronide) is a metabolite your body produces after processing alcohol. Unlike a breathalyzer, which only catches alcohol while it’s still in your system, an EtG urine test can detect drinking days after the fact. Results are reported in nanograms per milliliter (ng/mL), and interpretation depends heavily on which cutoff the testing program uses.
Three cutoff levels are standard:
- 100 ng/mL cutoff: The most sensitive. It detects over 76% of light drinking within two days and roughly 79% of heavy drinking up to five days later. This cutoff is commonly used in clinical and research settings to maximize detection. The tradeoff is a higher chance of false positives.
- 200 ng/mL cutoff: A middle ground. It catches over 55% of light drinking and over 66% of heavy drinking across a five-day window, with fewer false positives than the 100 ng/mL cutoff. Programs where a false positive carries serious consequences, like legal or employment monitoring, often prefer this threshold.
- 500 ng/mL cutoff: The least sensitive. It primarily detects heavy drinking within the previous day (78% detection rate on day one) and misses most light drinking after 24 hours. A result above 500 ng/mL is a strong indicator of recent, substantial alcohol use.
If your result is below the cutoff, it’s reported as negative. A result above the cutoff is positive, but the number itself doesn’t tell you exactly how many drinks someone had or precisely when they drank. Higher values generally suggest heavier or more recent drinking, but individual metabolism, hydration, and kidney function all affect the number. “Heavy drinking” in these studies means more than three standard drinks for women or four for men in a single day.
False Positives on EtG Tests
EtG tests can occasionally flag positive without intentional alcohol consumption. Chloral hydrate, a sedative medication, has been documented to cause false positives on EtG immunoassay screening. Incidental exposure to alcohol through hand sanitizers, mouthwash, or certain medications containing ethanol can also produce low-level positive results. This is one reason many monitoring programs use the 200 ng/mL or 500 ng/mL cutoff rather than 100 ng/mL: higher thresholds filter out most incidental exposure. If a screening result is disputed, confirmatory testing with more precise laboratory methods can distinguish a true positive from a false one.
PEth Blood Test Results
Phosphatidylethanol, or PEth, is a substance that forms in red blood cell membranes when alcohol is present. Because red blood cells live for about 120 days, PEth can reflect drinking patterns over the previous three to four weeks rather than just the past few hours or days. Results are reported in nanograms per milliliter (ng/mL).
The cutoffs used in practice vary somewhat, but general interpretation looks like this:
- Below about 8 ng/mL: Consistent with abstinence or very minimal drinking.
- 8 to 20 ng/mL: A gray zone. Some light drinking may have occurred, but PEth is not reliable at distinguishing abstinence from occasional, light use.
- 20 ng/mL or higher: Widely used as the threshold indicating moderate to heavy consumption.
- Above ~28 ng/mL: Associated with moderate, regular consumption in studies of healthy adults.
One study of trauma patients found that levels at or above 18.3 ng/mL suggested alcohol misuse, while levels at or above 23.9 ng/mL pointed to severe misuse. The key limitation of PEth testing is that it cannot reliably distinguish someone who is completely abstinent from someone who drinks very lightly. It’s most useful for identifying sustained, heavier patterns of use.
Hair Follicle Test Results
Hair testing measures EtG that has been incorporated into the hair shaft as it grows. Since scalp hair grows about one centimeter per month, a standard 3-centimeter sample covers roughly three months of history. Results are reported in picograms per milligram (pg/mg).
The Society of Hair Testing provides the most widely referenced cutoffs:
- 5 pg/mg or below: Does not contradict self-reported abstinence. This doesn’t guarantee zero drinking occurred, but it’s consistent with an abstinence claim.
- Above 5 pg/mg but below 30 pg/mg: Strongly suggests repeated alcohol consumption, roughly equivalent to regular drinking of more than about 10 grams of ethanol per day (less than one standard drink daily).
- 30 pg/mg or higher: Strongly suggests chronic excessive consumption, corresponding to an average intake of 60 grams or more of ethanol per day (about four to five standard drinks daily).
Hair tests are commonly used in custody disputes, professional licensing reviews, and liver transplant evaluations. They’re valued for their long detection window, but they don’t pinpoint specific drinking episodes. A result of 15 pg/mg, for instance, tells you someone has been drinking regularly over recent months, but it can’t tell you which days or how much on any given occasion. Hair treatments, color, and growth rate can all influence results to some degree.
Which Test Covers Which Timeframe
The type of test determines how far back it can look. Breath and standard blood tests only detect alcohol while it’s actively circulating, typically within 12 to 24 hours of the last drink. Urine EtG at the 100 ng/mL cutoff can pick up heavy drinking for up to five days and any drinking for roughly two days. PEth blood testing reflects patterns over the previous three to four weeks. Hair testing captures the longest window, covering approximately three months with a standard sample length.
If you’re trying to understand a result you’ve received, the most important things to identify are the type of test, the unit of measurement, and the cutoff your program or provider uses. A “positive” on a 100 ng/mL EtG screen means something very different from a “positive” on a 500 ng/mL screen, even though both say the same word on the report. When in doubt, ask the ordering provider or testing facility what cutoff was applied and what your specific number means in context.