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USDTL Research

Testing Nails for Drugs

by Douglas Lewis, DSc, President, Scientific Director, USDTL

Testing nails for drugs has been a useful tool for more than twenty five years. It has only been in recent years, however, that fingernails have been re-evaluated as a forensic matrix with utility to provide better detection for certain drugs and even provide a degree of dose-response relationship. Studies conducted in the late 1980’s on anti-fungal drugs used to treat fungal infected nails showed that fingernails and toenails grew not only in length from germinal matrix but continually in thickness from the distal matrix, thus drugs and metabolites were added from the beginning of nail growth and then all along the ventral surface as the nails grew in length. When the nail emerges from the matrix, there is a one to two week lag until the nail is sufficiently long enough to safely clip and collect a specimen. This lag is similar to the time hair takes to grow up from the follicle and emerge above the scalp line high enough to cut safely. Nails have a distinct advantage over hair. Hair is often treated cosmetically with agents such as bleaches, dyes, permanents andstraighteners that destroy drug substances in the hair thereby reducing or eliminating the presence of the offending substances. Nails are not treated in the same manner. Nail polishes have not been shown to be effective adulterants. Prosthetic nails are like hair weaves, a substitution and not a valid specimen.

ETG Sensitivity in Fingernail vs Hair

In a recent study, 606 college students provided detailed alcohol consumption histories via the time-line, follow-back technique along with hair and fingernail specimens for alcohol biomarker ethyl glucuronide (EtG) analysis. A detailed breakdown of the data showed that male fingernail and hair EtG strongly correlated with reported alcohol histories. Female fingernail EtG had the same strong correlation but hair EtG showed a diminished correlation when compared to male peers. Additionally, the mean fingernail EtG concentration for all positive specimens was 2.5 times the mean hair concentrations. While the data did not allow any inferences other than gender difference, previous data that showed EtG susceptibility to peroxide oxidation suggests that cosmetic treatment of hair may be a biasing factor.

Carboxy-THC Sensitivity in Fingernail vs Hair

In another recent study, de-identified, paired hair-fingernail specimens were analyzed for Carboxy-THC at the SAMHSA Proposed Mandatory Guidelines for Federal Workplace Drug Testing Confirmation Cut Off concentration of 0.05 pg/mg (50 fg/mg). Of the 120 specimens tested, 31% of the hair specimens tested positive with a mean concentration of 854 fg/mg, while 41% of the fingernail specimens tested positive with a mean concentration of 4662 fg/mg. Positive Carboxy-THC in fingernail specimens were on average 5.5 times higher than positive hair specimens.

What is the Window of Detection?

A frequent question that arises concerning nail testing is “What is the window of detection for fingernails?” There are a limited number of references in the literature that fully describe the window of detection of nail as a drug testing specimen type. But, this information is not critical for our intended applications. The available literature indicate that some drugs wash out as quickly as 3 months while some can be retained for many more months. The theoretical upper limit is the age of the nail material, which for the average person is 5-6 months minus the washout rate. However, some individuals may have slighter faster nail growth while others may have slightly slower. Also, a major consideration in the detection window is how high the original drug exposure level was. What we know is that nail has a long window of detection; longer in some instances than hair and that some compounds in nails may have predictable dose-response relationships. Fingernails show much promise in the forensic toxicology area. They allow analysis for compounds that can be difficult to monitor in body fluids and easily adulterated in hair but accumulate and can be detected and quantified in fingernails.

2012 is Douglas Lewis’ 21st year as president and scientific director of USDTL. Prior to USDTL, he spent five years as an assistant professor of clinical pathology at Northwestern University Medical School while also serving as the head of the toxicology section at the Children’s Memorial Hospital in Chicago. During his tenure at Northwestern and Children’s, Lewis established the first non-Olympic anabolic steroids testing lab in the United States and was a toxicologist for the U.S. Weight Lifting Federation. He also developed new specimens such as meconium for use in diagnosing substance-exposed newborns.


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