Hair, nail, blood or urine: choosing the right sample
No single sample type answers every question. The right choice starts from what the case needs to show — recent use, a pattern over months, or abstinence — and works back to the sample that can show it.
The decision
Start with the question, not the sample
Every instruction is really one of three questions. Has this person used recently? — choose a short-window sample: oral fluid or urine. What is the pattern over months? — choose a long-window sample: hair or nails. Have they stayed abstinent? — usually a long-window sample, often supported by repeat short-window tests or a blood marker. Answer that first question and the sample choice largely makes itself.
The sample types at a glance
- Oral fluid — the shortest window, reflecting very recent use. Quick and non-invasive to collect, well suited to workplace programmes, post-incident and for-cause testing.
- Urine — the workhorse for recent use, covering roughly the last few days depending on the substance. Widely used in court work alongside hair.
- Hair — the timeline sample. Around one centimetre of head hair reflects roughly one month, so a standard sample evidences a pattern across months, and segmentation can show whether use is increasing, decreasing or absent. See the complete hair testing guide.
- Nails — the alternative long-window sample. Fingernails cover around 3 to 6 months; toenails look back longer. The usual choice where head and body hair are unavailable or heavily treated.
- Blood (including PEth) — for specific questions. PEth is an alcohol marker in blood reflecting roughly the previous two to four weeks of drinking, sitting neatly between a breath test's hours and hair alcohol markers' months.
This page is a general guide. It is not legal, medical or technical advice. Laws, guidance and laboratory methods change, so check the current requirements for your own case. Detection windows are indicative. They vary with the substance, dose, how often it is used and the individual. Last reviewed .
When hair is not an option
Hair is the default long-window sample, but it is not always available — the donor may have very short hair, no body hair, or hair so heavily bleached that interpretation would be compromised. Nail testing exists for exactly these cases: clippings are simple to collect under chain of custody and cover a period of months. A case is never stuck because the obvious sample is unavailable.
Combining samples: the strongest instructions
In family and care proceedings, the strongest instructions usually combine windows. A hair test alone shows the pattern over months but not the last few days; a urine test alone shows recent days but no history. Together they close the gap. Similarly, hair alcohol markers combined with PEth give both the long pattern and the recent weeks — useful where abstinence is claimed and the court wants it checked across both timescales.
Workplace programmes
For workplace testing the calculus is different: speed, scale and dignity at collection matter alongside the window. Oral fluid screening on site, backed by ISO 17025 accredited laboratory confirmation, covers most workplace scenarios, with hair reserved for pre-employment checks in safety-critical roles. The employer’s guide covers this in depth.
What every sample type has in common
Whatever the sample, the result is only as strong as the process around it: collection under chain of custody, analysis in an ISO 17025 accredited laboratories, and reporting fit for the purpose it was instructed for. NIVHA applies one professional standard across every sample type — there are no home kits and no shortcuts.
Common questions
Sample choice — your questions answered
Which drug test goes back the furthest?
Hair testing looks back the furthest of the routine sample types — a standard 3 cm head hair sample reflects roughly the previous three months, and longer samples can look back further. Nail testing also covers a period of months and is the usual alternative where hair is unavailable.
What is the best test for very recent use?
Oral fluid has the shortest window and is well suited to detecting very recent use, which makes it the usual choice for post-incident and for-cause workplace testing. Urine covers roughly the last few days, depending on the substance.
Can a test be beaten by shaving or dyeing hair?
Where head hair is unavailable, body hair can usually be used instead, and nail samples are a further alternative — so removing hair does not put testing out of reach. Cosmetic treatments such as bleaching can reduce some substance levels and must be disclosed. They are taken into account, although heavy bleaching can make a negative result unreliable.
What is PEth testing?
PEth (phosphatidylethanol) is a blood marker of alcohol consumption that reflects roughly the previous two to four weeks of drinking, and longer after heavy drinking. It is often instructed alongside hair alcohol markers because the two windows complement each other — hair shows the pattern over months, PEth shows the more recent weeks.
Can different sample types be combined in one instruction?
Yes, and in court work they usually are. A common combination is hair plus urine — the hair evidencing the pattern over months and the urine the recent snapshot. We will recommend the right combination for what your case needs to show.
Not sure which test your case needs?
Tell us what you need to show and we will recommend the right sample, or combination, in confidence.