Nailing Drug and Alcohol Testing: The Use of Fingernails as an Alternative to Hair Testing

DATIA Focus Magazine, Summer 2014

By Joseph Salerno, United States Drug Testing Laboratories

Sourced by USDTL© Laboratory

Fingernail Testing Has Many Similarities to Hair Testing, As Well As Some Advantages Including Ease of Collection, Stability, and a Longer Window of Detection

Substance abuse in the 21st century is an ever-evolving and sophisticated animal. Through the Internet, new drugs—both illicit and prescription—are available in dizzying arrays. Along with the new drugs being abused are new methods to avoid detection. Labs must maintain constant research and development to meet the needs of the ever-changing market. Thankfully, the old adage ‘you are what you eat’ still rings true.

Hair testing has caught on as a popular sample to detect substances of abuse and so has the ability of the abuser to Google ways to offset drug tests. In an effort to remain ahead of the curve in this complex market, researchers have turned to other sample types to go beyond the limits of hair testing. Fingernails are composed of keratin, the same protein matrix found in hair. Fingernail testing has many similarities to hair testing, as well as some advantages including ease of collection, stability, and a longer window of detection. The detection of substances in fingernails provides a powerful tool for the drug and alcohol testing industry.

Incorporation of Drug and Alcohol Biomarkers in Nail Samples

Fingernail keratin is four times thicker than that found in hair. While hair grows only in length from the hair root, nail keratin grows in two directions. From the germinal matrix, fingernails grow in length as they emerge from the nail root. As they elongate, fingernails also grow in thickness with new keratin being added to the underside of the fingernail along the nail bed (Figure 1). It was previously thought that substances could only enter the fingernail from the germinal matrix, but research on therapeutic drug monitoring has debunked this model of drug capture. Blood vessels in the nail bed continuously feed the growing fingernail. As a result, drug and alcohol biomarkers are trapped in the keratin matrix over the entire fingernail as it grows in length. Fingernails are a reservoir matrix made up of a tight weave of keratin fibers that are also porous. This tight but porous nature means that nails are a superb matrix for catching and trapping drug and alcohol biomarkers. Chronic drug or alcohol use causes a continuous build-up of biomarkers along the entire fingernail as it grows.

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