How Often Do Fingernail Drug Tests Come Back With a False Positive Drug Test

How do hair and fingernail drug testing compare?

There are many different drug testing methods out there, and while the majority of our clients use hair testing, we will sometimes use fingernail testing when the former is simply not possible.

The two have plenty of similarities, but also a number of differences. If you're unsure as to which to choose and when, read on for our guide to both: how they work, how they are used, and their benefits and limitations.

Hair Testing

How does it work?

Hair testing identifies drug and alcohol markers both inside and outside a shaft of hair. When the sample arrives in the laboratory for testing, it is first washed to remove external contamination before any testing takes place. Then, also using cut-offs, the detection of metabolites is further confirmation of actual consumption as opposed to contamination. In the case of drugs, the test allows the lab to measure the number of drugs and their metabolites in the hair shaft. For alcohol, it establishes whether certain biomarkers of alcohol consumption are present in the hair. Learn more about the process here .

What are hair tests used for?

Hair drug and alcohol testing is a reliable means of establishing an individual's history of drug or alcohol consumption, distinguishing between casual and chronic use, and detecting usage over a period of up to 12 months.

What drug and alcohol use does hair testing show?

The exact number of substances tested for varies from laboratory to laboratory. At Cansford, we have the ability to test for 120 substances: alcohol, plus drugs in categories including antidepressants, steroids, new psychoactive substances (i.e. 'legal highs',) opiates and more. Contact us for a full list.

What are the cut-offs for hair testing?

A cut-off is the point which determines whether a test result is positive or negative. When the amount of drugs or alcohol in the system are below the cut-off, they are considered as "Not Detected" or "Negative". When they are above the cut-off, they are considered "Detected" or "Positive".

Cut-offs vary depending on the substance being tested for - and may also vary depending on the methodology used and the laboratory conducting the analysis. Recommended cut-off levels can be found in the Society of Hair Testing Guidelines .

What is the collections process for hair testing?

Hair samples are generally collected under controlled conditions, and by a trained collector. They are immediately wrapped and labelled, before being sealed in a tamper-proof envelope and sent to the testing laboratory. Read more about the collections process here .

What are the benefits of hair testing?

Hair testing is chosen for its accuracy and its ability to determine long term patterns of use. It offers the widest window for detection of any testing method: 0-6 months for alcohol, and 7 days to 12 months (or more) for drugs, depending on the length of the hair.

What are the limitations of hair testing?

Hair samples can be subject to external contamination , as a result of being in close contact with drug users. However, as noted before, if procedures are followed properly, the risk of false positives through external contamination is extremely rare.

While hair testing can paint a long term picture of drug use, it cannot pinpoint the exact date of usage, nor can it confirm the context of use - unless the lab is informed of anything that might affect the test results.

What else do you need to know?

Hair testing is one of the most expensive forms of drug testing, however, its accuracy is second to none - and it can be conducted even if the subject is bald , or if they try to cheat the system . In addition, a hair test can replace many separate urine or oral fluid tests, making it an ideal sample to prove abstinence.

Fingernail Testing

How does it work?

Like hair, fingernails are composed of keratin. Substances are able to pass into the nail as it is formed and from the blood vessels under the nails into the keratin fibres of the nails themselves and become trapped. As the nails grow longer and thicker, the layers provide a history of substance use. Testing can be conducted in two different ways, either using immunoassay screening followed by a confirmation test, or with liquid chromatography and mass spectrometry .

What are fingernail tests used for?

Fingernail drug tests are commonly used in situations where hair testing is the preferred method, but where hair collection is challenging. If a person can't have their hair cut for religious reasons, for instance, or people who have little to no body hair to test.

What drug and alcohol use does fingernail testing show?

As well as testing for EtG alcohol markers, fingernail drug tests can confirm the presence of drugs including opiates, cocaine, amphetamines, barbiturates and benzodiazepines. Depending on the numbers of tests requested, these tests can also cover substances like fentanyl, tramadol and ketamine.

There are two types of fingernail drug test: screening tests (or presumptive tests), which are qualitative tests to establish whether a drug is present, and confirmation tests (or definitive tests) - quantitative tests confirming which drugs are present, and in what quantity.

What are the cut-offs for fingernail testing?

Despite having been around since the 1980s, it is only in recent years that fingernail testing has come to the fore. As such there are currently no industry-wide standards for the method, and cut-off levels will vary from laboratory to laboratory.

What is the collections process for fingernail testing?

The optimum sample size for both screening and confirmation testing is 10mg which equates to approximately 2-3 mm clippings from one fingernail. Sampling all ten fingernails could produce a sample weight of 100mg. If the fingernails are not sufficiently long, samples can be taken from the toenails instead.

The donor clips the samples in front of a trained collector, using clippers that have been cleaned and after washing their hands and cleaning under their nails. The sample is secured in a clearly labelled envelope, before being sent to the lab for analysis.

What are the benefits of fingernail testing?

Fingernail testing - unlike urine and blood testing - can be used to test within a timeframe of months, rather than days. A three millimetre sample of nail can provide an exposure history of up to (approximately) eight months. A three millimetre fingernail clipping might represent six months and the same from a toenail 12 months. The collection method is less intrusive than methods like blood testing, and with samples given in front of collections staff, there is little risk of tampering.

What are the limitations of fingernail testing?

While fingernail drug testing can look back at up to eight months of substance usage, it cannot establish the exact pattern of drug use which can be seen in hair testing.

Sample collection is only possible if fingernails or toenails are long enough, and the condition of the nails is vital: nails must have a normal appearance, and be free of contaminants - including dirt, oil, nail polish and false nails. In addition, toenail samples must not be collected if the donor suffers from peripheral artery disease or diabetes.

Fingernail testing cannot be used to establish recent drug usage: substances can only be identified in fingernails between two and four weeks after ingestion. It is also unsuitable for confirming one-time substance use, as it is unlikely that the drug will have made it into the keratin.

What else do you need to know?

Fingernail drug testing is the closest alternative to hair testing - if the latter is not possible.

How Often Do Fingernail Drug Tests Come Back With a False Positive Drug Test

Source: https://blog.cansfordlabs.co.uk/the-differences-between-hair-and-fingernail-drug-testing

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