If you want to demonstrate alcohol use, for a CBR procedure, a new job, or your own peace of mind, a lab looks at specific biomarkers. CDT in blood reflects chronic use over roughly the past two to three weeks. EtG in hair can look back around three months. Which test suits you depends on the question you want answered.
Most people searching for this have a concrete reason: a CBR investigation into driving fitness, a job where sobriety matters, or simply wanting to show themselves they are clean. Below you will read what each alcohol marker measures, how far back it looks, and what an abnormal value can mean.
How do you prove alcohol use with a test?
Proving alcohol use can be done in three ways, depending on the time window. CDT in blood points to sustained heavy use over the past two to three weeks. EtG in hair captures use over a longer period, roughly one month per centimetre of hair. PEth in blood sits between those windows. A home test strip only gives a yes/no signal and is unsuitable here.
The difference lies in the matrix, the biological material analysed. A lab quantifies an exact value per marker with a reference range, instead of a faint line. In a borderline case, that distinction can make the difference between doubt and a result you can support.
What is a CDT test and how far back does it look?
CDT stands for carbohydrate-deficient transferrin, a form of the iron-transport protein transferrin that rises with prolonged heavy alcohol use. The most common result is a percentage (%CDT), with the same reference value of below 2.8% for men and women. CDT looks back roughly two to three weeks.
The half-life of CDT is around 14 to 17 days. With full abstinence, an elevated value usually falls back toward normal within two to three weeks, though after prolonged heavy use it can take longer. CDT is therefore mainly a marker of a pattern, not of a single drink. If you want one marker measured specifically, a CDT test for alcohol can quantify that value for you.
Which blood values does the CBR use for alcohol?
In an investigation into driving fitness, the CBR does not look at a single number but at a combination of blood values. A frequently used set is gamma-GT, CDT and MCV. If all three are elevated, that points to a pattern of chronic excessive use; one abnormal value alone says less.
- Gamma-GT (GGT): a liver enzyme, reference roughly 10 to 40 in men and 6 to 25 in women. Can also rise from liver or gallbladder conditions and some medications.
- CDT (%CDT): reference below 2.8%. The most specific of the three for alcohol, with a look-back window of two to three weeks.
- ASAT/ALAT: liver enzymes that can indicate strain; markedly elevated values point to a greater load.
- MCV: the average size of red blood cells, which can be elevated after prolonged heavy use.
The CBR weighs these values together with an interview and the reason for the referral. The result of a single test therefore does not decide the outcome of a procedure on its own. What a separate test does do is give you insight beforehand into where you stand.
What is the difference between CDT, EtG and PEth?
CDT, EtG and PEth each measure alcohol use in their own way and over their own window. CDT is an indirect marker in blood, EtG is a direct breakdown product measured in urine or hair, and PEth is a direct marker in blood. The table below sets the differences side by side.
| Marker | Matrix | Look-back window | What it mainly shows |
|---|---|---|---|
| CDT (%CDT) | Blood | ± 2 to 3 weeks | Pattern of chronic heavy use |
| EtG (hair) | Hair | ± 1 month per cm, up to ± 3 months | Use over a longer period |
| EtG (urine) | Urine | ± 1 to 3 days | Recent use |
| PEth | Blood | ± 2 to 4 weeks | More recent pattern, sensitive |
No single marker is the right one for every question. For a long look back, hair analysis may fit better; for a pattern over recent weeks, CDT is often used. For the related question of how long substances stay detectable, read more in our overview of how long drugs stay detectable.
Can a CDT value be too high without heavy drinking?
Yes, it can. An elevated %CDT usually relates to sustained alcohol use, but not always. A number of factors can influence the value without heavy drinking, which is why a lab never looks at CDT alone.
- Rare inherited disorders in the sugar chains of proteins (CDG variants) can raise %CDT.
- Severe liver conditions can disturb the transferrin pattern.
- A recent blood transfusion can affect the measurement.
A quantified lab value with a reference range offers more grip here than a home strip, because the result can be placed in context. What an abnormal value means for you personally is best discussed with a doctor.
How do you prove that you are sober?
Showing that you drink little or nothing calls for a marker that matches the period you want to cover. For recent weeks, a CDT value within the reference range can support that pattern; for a longer look back, an EtG hair test is sometimes used. A single measurement is a snapshot; a repeated measurement shows a line over time.
At Zuivertest you choose which marker to have measured, only you see the result, and every result comes with an assessment by a BIG-registered doctor. You can have the CDT marker measured on its own or as part of a broader panel.
Frequently asked questions
How long does alcohol stay detectable in blood?
Alcohol itself is usually measurable in blood for a few hours up to about a day. Markers of a use pattern, such as CDT, look back further: roughly two to three weeks.
Does a CDT test show whether I drank yesterday?
No. CDT responds to sustained heavy use over weeks, not to a single evening. For very recent use, other markers, such as EtG in urine, are more suitable.
Do I need a referral for an alcohol test?
Not at Zuivertest. You order online, we arrange the lab referral via ZorgDomein, and you have blood drawn at a lab near you.
Can my employer or the CBR see my result?
No. A test ordered through Zuivertest sits behind your own secured account. Only you decide whether to share the result.
Every blood test result at Zuivertest includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
Sources
- Jellinek, "Which blood tests does the CBR use?" (jellinek.nl)
- Richtlijnendatabase, "Laboratory testing for alcohol misuse in driving-fitness assessments" (richtlijnendatabase.nl)
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