Testing information
Reading a hair alcohol result
An alcohol result arrives as one number in picograms per milligram. This is what that number is read against, what each finding supports, and the four things it cannot settle on its own.
- The three international bands
- What each finding supports
- Limits stated plainly
What was found is exact. When it happened is an estimate.
Which substances are in the hair, and how much of each, is measured to a very high degree of certainty. The laboratory uses mass spectrometry, which identifies a molecule by its mass rather than inferring it from a colour change or a reaction. A positive result is a positive result.
Dating that use is the approximate part. Hair does not all grow at the same speed, individual follicles grow at slightly different rates, and some are resting at any given time. It is the same reason a haircut never grows out perfectly evenly. So a length of hair corresponds to an approximate period, not to a particular day.
These are two separate questions, and this is the part worth being clear about: an estimated timeline does not make the substance finding any less reliable. The chemistry is precise. The calendar is approximate.
What the certificate measures
The body produces ethyl glucuronide, EtG, only once alcohol has been consumed and metabolised, and a small amount of it is incorporated into hair as the hair grows. The laboratory measures how much, in picograms per milligram: a picogram is a trillionth of a gram, which is why the numbers look large beside the thresholds. Reporting begins at 5 pg/mg, and the figure is then read against three bands agreed internationally rather than set by any one laboratory.
No significant alcohol use; not inconsistent with abstinence. May reflect incidental or environmental exposure.
Moderate consumption, such as regular social drinking.
Heavy or chronic use, indicative of frequent consumption.
| Finding | Concentration | Indicates |
|---|---|---|
| Abstinent or very irregular consumption | < 5 pg/mg | No significant alcohol use; not inconsistent with abstinence. May reflect incidental or environmental exposure. |
| Regular consumption | 5 – 30 pg/mg | Moderate consumption, such as regular social drinking. |
| Chronic excessive consumption | > 30 pg/mg | Heavy or chronic use, indicative of frequent consumption. |
Bands from the Society of Hair Testing's Consensus on Alcohol Markers (2019 revision)
What each finding supports, and what it does not
A band is a description of an average, and each one carries its own limits. Set out plainly, because these are the points that get argued, and a reader who meets them here is not meeting them for the first time across a table.
Abstinent or very irregular consumption
< 5 pg/mg
What it supports. A result in this band is consistent with abstinence, and it is the finding most often sought where someone has undertaken not to drink.
What it does not. It is not a certificate of abstinence. Very low readings can also come from alcohol in everyday products rather than from drinking, and a person who drank only within the fortnight before collection may not yet have grown the hair that would record it.
Regular consumption
5 – 30 pg/mg
What it supports. A result here is consistent with ordinary social drinking sustained across the period tested, rather than with either abstinence or heavy use.
What it does not. It cannot separate a glass most evenings from a heavier weekend and five dry days. Both produce the same average, and the average is what the hair records.
Chronic excessive consumption
> 30 pg/mg
What it supports. A result in this band is consistent with heavy or sustained consumption across the period tested, and it is the finding that most often prompts a request for interpretation.
What it does not. It is a description of consumption, not a clinical diagnosis. Dependence is assessed by a clinician, not measured in hair, and no concentration establishes it on its own.
Four things a concentration cannot settle
Most questions that follow a hair alcohol result are one of these four, and the answer to each is a property of the method rather than of the laboratory.
A date
A segment is an average of everything in it. A 3 cm sample covers roughly three months and reports one figure for the whole of it, so a result cannot place drinking in a particular week, or on a particular day.
A number of drinks
No laboratory reports drinks, because the arithmetic does not work. Alcohol is metabolised at different rates by different people, and hair type and cosmetic treatment shift how much EtG is measured from the same consumption.
A pattern
Steady drinking and episodic drinking that average the same across the period produce the same band. Where the distinction matters, segmenting the sample month by month shows the shape that a single figure hides.
A diagnosis
A band describes what was consumed, not what it means clinically. Alcohol use disorder is a clinical assessment made by a treating practitioner, and a hair result is one piece of information a clinician might consider.
The question underneath most of these is how much drinking a given band represents. How many drinks a day show up in a hair alcohol test works through what each band looks like in practice.
If a result is disputed
A concentration on its own is rarely the end of a matter, and where one is being relied on, the questions that decide its weight are the period the segment actually covers, whether the hair was cosmetically treated, whether external exposure could contribute, and whether the pattern implied is the only one the figure supports. A forensic interpretation report addresses those in writing.
Dr Michael Robertson interprets hair, blood, urine, saliva and breath results regardless of who conducted the testing, so a result from another provider or another method can be reviewed. Instructions come through this clinic, and reports start from $495.
Can a shorter period be looked at on its own?
Yes. A sample can be segmented so that each centimetre is analysed separately, which turns one averaged figure into a month-by-month sequence and is what shows a change over the period rather than a single number covering all of it. The arrangement is set out on the hair alcohol testing page.
Why FAEE markers are not reported
The Society of Hair Testing removed fatty acid ethyl esters from its Consensus on Alcohol Markers at the 2019 revision, having earlier removed them from its proficiency testing programme, for lack of uniformity in how FAEE results were analysed and interpreted. EtG is the marker the current consensus is built on, and it is the marker reported here.
Can a result from another laboratory be reviewed?
Yes. An interpretation is an opinion on what a result supports, and it does not depend on who produced the result or on which sample type was used. Hair, blood, urine, saliva and breath results are all within scope, and a report can address a result issued by any provider.
Common questions about hair alcohol results
What do the EtG levels on a hair alcohol test generally indicate?
Hair alcohol results are reported as ethyl glucuronide (EtG) in picograms per milligram of hair and read against three internationally agreed bands. Below 5 pg/mg is consistent with abstinence or very irregular consumption; 5 – 30 pg/mg indicates regular consumption such as social drinking; above 30 pg/mg indicates chronic excessive consumption. The bands come from the Society of Hair Testing's Consensus on Alcohol Markers, 2019 revision. Each describes an average across the whole period tested, not a measurement of any single occasion.
Is a low EtG result proof that someone has not been drinking?
It is strong evidence, but it is not proof, and an honest report says so. A result below 5 pg/mg is not inconsistent with abstinence, which is the way the standard itself is worded. Two things can produce a low figure other than not drinking: alcohol in everyday products such as some hair preparations and mouthwashes can contribute externally, and hair takes roughly a fortnight to grow above the scalp, so very recent consumption may not be in the sample yet.
Can a hair alcohol test say how many drinks a day someone had?
No, and no hair alcohol test can. The laboratory reports a concentration, and a concentration cannot be converted into drinks. Individual metabolism, hair growth rate, hair type and cosmetic treatment all change how much EtG is incorporated from the same consumption, and the same weekly volume taken in one sitting or spread across a week produces the same average. What the result establishes is the band the average falls in.
Can a hair alcohol result be challenged?
Yes. A concentration is a starting point, not a conclusion, and the arguments that bear on it are well established: the period the segment actually covers, cosmetic treatment, external exposure, and whether the pattern the figure implies is the only pattern consistent with it. A forensic toxicologist's report sets out what the result does and does not support. Dr Michael Robertson interprets hair, blood, urine, saliva and breath results regardless of who conducted the testing, and is instructed through this clinic.
Does a hair alcohol test detect alcohol the way a breath test does?
No, and the two answer different questions. A breath test measures alcohol present now and speaks to impairment at that moment. A hair test measures EtG, a by-product the body produces only after alcohol has been consumed and metabolised, and which is laid down in hair as it grows. Reporting begins at 5 pg/mg. It shows consumption across weeks and months rather than impairment on a day.
More on the full FAQ page.
Book a hair alcohol test
Alcohol (EtG) Hair Testing, $699, with EtG reported against the international bands above and results in 5–7 business days.