An EtG hair test looks back further than blood or urine. EtG, ethyl glucuronide, is a direct breakdown product of alcohol that lodges in the hair. Each centimetre of hair covers roughly one month, up to about three months with enough hair length.
That long window makes a hair test suitable for the question of whether someone has drunk little or nothing over a longer period.
How far back does an EtG hair test look?
Scalp hair grows on average about one centimetre per month. A three-centimetre segment therefore gives a picture of roughly the past three months. EtG in hair thus covers a much longer period than CDT in blood, which looks back about two to three weeks.
The choice depends on your question. For a pattern over recent weeks, CDT is often used; for a longer look back, hair analysis may fit better. I set the differences side by side in the overview of proving alcohol use.
How does EtG differ from CDT?
EtG is a direct marker: it is a breakdown product of alcohol itself. CDT is indirect: it measures a change in a transport protein from prolonged use. EtG in hair captures a long period, while CDT mainly shows a recent pattern. Both have their place, depending on the time window you want to cover.
For the related question of how long alcohol stays measurable per matrix, read how long alcohol is detectable.
Every blood test result at Zuivertest includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
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