Hair vs Nail Drug Testing

By Gail Evans, Technical Trainer at AlphaBiolabs
Last reviewed: 10/18/2023

Any drug that is consumed circulates in the bloodstream and a proportion of it and its metabolites become incorporated into the keratin that make up nails and hair.

This tough, fibrous protein traps any drugs and their biomarkers ready for detection. Therefore, both hair and nail testing can detect the same drugs.

Head hair drug testing

Head hair drug testing is considered the gold standard in toxicological analysis. This long-established method can provide a history of drug abuse and is routinely used in family law.

The accuracy of any hair drug analysis depends on both the sampling procedure and the laboratory techniques employed. Hair strand samples are normally collected by a trained sample collector.
he hair sample needs to be cut from the highest point of the scalp (the vertex) as this region is associated with least variation in growth rates. Ideally, the sample needs to contain around 200 individual strands (about the width of a pencil) and should be taken from a discrete area whenever possible.

If an individual has been in an environment heavily laden with a drug, detectable levels could be found on the hair sample due to smoke. In addition, it could be present due to direct transfer (such as by hands).

To avoid any such false positive results, each hair sample is chemically washed three times to remove or reduce any drug present prior to analysis. In addition, the Society of Hair Testing (SoHT) Guidelines for Drug Testing in Hair provide recommended cut-off levels to follow [1]. The washing solution can also be analyzed if required. For example, if an individual admits to being surrounded by marijuana smokers, the washing solution could be used to back up the test results. Any external exposure to drugs should be declared at the time of sample collection.

Excessive shampooing, some cosmetic treatments (such as dyeing, bleaching, perming and relaxing), and the use of thermal straighteners may reduce drug concentrations in hair to varying degrees. The extent of the loss will depend on the cosmetic treatment used and the drug present.

All hair treatments should therefore be declared at the time of sample collection and taken into consideration when reviewing the findings of a hair test.

Types of head hair drug tests

There are two types of head hair drug tests available: overview or segmented analysis. As head hair grows at an average rate of 1 cm each month, drug use can be established over a defined period depending on the length of hair selected.

An overview analysis is beneficial to obtain a general indication of drug use. This could range from 3 cm to identify drug use within that 3-month time period, up to 6 (2 x 3) or even 12 (4 x 3) months, dependent on the length of hair available.

Differing results from the 3-month overviews can help highlight patterns in drug use. If a more detailed analysis is needed, segmented would be the preferred option. By segmenting head hair samples into monthly 1 cm sections, a month-by-month profile of drug use can be attained to provide a detailed historical picture of an individual’s drug exposure.

Window of detection: from 1 month segmented up to a 12-month (4 x 3) overview.

Advantages: can effectively confirm long-term exposure to drugs over a defined period depending on the length of hair collected. Can also give detailed analysis on a month-by-month basis.

Body hair drug testing

Head hair strand testing is preferred as this can effectively confirm long-term exposure to drugs over a defined period depending on the length of hair collected. This is because head hair grows at a rate of 1 cm a month.

If head hair is not available alternative collection sites on the body could be considered including chest, back, arm, underarm and leg hair. The growth rate of hair from these alternate sites differs from head hair and as such cannot be used to determine a specific timeframe of drug use. Beard hair grows at a rate of 0.7 cm a month, so analysis of this type of hair can provide a more specific timeframe.

Hair strand samples are normally collected by a trained sample collector. Different types of body hair cannot be combined in one sample. Approximately 20–30 mg of sample needs to be collected. As with head hair drug testing, each body hair sample is chemically washed three times to remove or reduce any drug present prior to analysis. This is to avoid any false positive results from direct transfer (such as by hands), or due to your client being in an environment heavily laden with smoke.

Window of detection: up to a 12-month overview (beard hair can provide a more specific timeframe, dependent on its length).

Advantages: useful if head hair or sufficient nail clippings are not available. Hair can be collected from chest, back, arm, underarm, leg and beards.

Nail drug testing

Nail analysis can provide detailed information about drug consumption and is a highly stable, simple-to-collect and easy-to-transport sample.

The clippings need to be taken as near to the nail bed as possible. Approximately 20 mg of nail is required for the test. If the nail is long (5 mm or above) then only one would be required. If the nails are short then it may be best to take clippings from several nails. Toe nails as well as finger nails can be used, but not a mixture of both. The advantages of using toe nails is that there is less potential for environmental exposure.

It is preferable that nails with shellac or acrylic nails are not used. However, if either of these are present they must be removed prior to the sample collection.

Window of detection: up to a 12-month overview

Advantages: useful when hair drug testing is not available.