What is a cut-off value in a drug test?

You used a test strip, you see one faint line, and you wonder: does a trace already count as positive? The answer is fixed in a single number most people never get to see: the cut-off value. It is the threshold above which a test calls a result positive. If the measured concentration falls below it, the result is called negative, even though a minute amount is present.

That threshold is not a detail; it is the core of what makes a drug test reliable. Without a cut-off, every insignificant contamination would set off an alarm. We believe a good test should not give the most sensitive result, but the most interpretable one, and that is exactly what a well-chosen cut-off makes possible.

What a cut-off value actually is

Every substance has an agreed cut-off, almost always expressed in nanograms per millilitre (ng/mL). A laboratory works with two levels. The first, rapid screening uses a wider threshold. If the value exceeds it, a confirmation analysis follows with a much sharper, substance-specific method (GC-MS or LC-MS) and a lower cut-off. Only when both steps cross the threshold does the result formally count as positive.

The figures below are commonly used reference values for urine. They differ per laboratory and per guideline, so treat them as orientation, not as a fixed law.

What stands out: the confirmation threshold is often lower than the screening threshold. That is deliberate. Screening may be slightly wider so as not to miss positive cases, while confirmation measures sharply and specifically. The Trimbos Institute, the Dutch knowledge centre for substance use, and the RIVM both point out that the chosen threshold directly determines how much use stays "under the radar".

Why the cut-off determines what you see

A high cut-off means light or older exposure comes out negative. A low cut-off catches more, but raises the chance that passive or negligible exposure already counts. The threshold is therefore a trade-off between sensitivity and relevance, not a sign of a better or worse test.

The big advantage of a laboratory test is that you do not just hear "positive or negative", but receive a quantified value: how far you sit above or below the threshold. A line on a home test never gives that. How a test strip compares to a lab analysis is explained in home drug test vs lab test.

Cut-off and the detection window

The cut-off works together with the detection window. After use, a substance gradually falls below the threshold. The moment that happens is exactly the end of the detection window. A higher cut-off shortens that window, a lower one lengthens it. So the same use event can still be positive at one threshold and already negative at another. The full per-substance overview is in how long do drugs stay detectable.

Cut-off, sensitivity and specificity

Behind the threshold sit two concepts that are often confused. Sensitivity is the chance that a test actually picks up use; specificity is the chance that a negative result is genuinely correct. A low cut-off raises sensitivity but lowers specificity: you catch more real cases, but also more noise. A high cut-off does the opposite. The figures in the table are therefore not an arbitrary choice, but the result of that trade-off, set in international guidelines and adopted by Dutch laboratories.

Worth remembering: a measured value says something about the concentration present, not about how much you used or when. Two people with the same result may have used at very different moments and in very different amounts. The cut-off tells you whether the substance sits above the agreed threshold, no more than that.

Common question: does a value just below the cut-off count?

Formally, no. A value just below the threshold counts as negative, even if something measurable is present. That can feel contradictory, but it is deliberate: without that lower bound, measurement and background noise would constantly produce positive results. It is precisely for this reason that the Trimbos Institute and the RIVM recommend a confirmation step before any consequences are attached to a result. A quantified lab value also shows how close you sit to the threshold, information a line on a home test never gives.

If you want a quantified result instead of a line, you can turn to the core 5-panel or the extended 10-panel, where each value is set against an established cut-off. The difference between a screening and a confirmed measurement is explained in home drug test vs lab test.

Every test result at Zuivertest includes a professional assessment from a BIG-registered doctor. A drug test can provide clarity, but does not replace medical advice. For treatment decisions, discuss your results with your GP.

Sources

• Trimbos Institute, National Drug Monitor, substance use in the Netherlands (trimbos.nl)
• RIVM, information on drugs and detection (rivm.nl)