College of American Pathologists
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  Q & A





cap today



April 2007

Q: Within the past couple of years, I’ve seen drugs-of-abuse screening tests performed on human hair matrices instead of urine samples. Is it possible to detect and analyze long-term or chronic exposure to toxic heavy metals, such as mercury or lead, using human hair? If certain abused drugs can build up in hair follicles over time, can the same be said for mercury, lead, arsenic, and cadmium?

A. Hair from the human head has been used for years to detect metals in cases of chronic exposure or extended poisoning. As with drugs of abuse deposited in hair, however, there are caveats, some of which are unique to metals. For example, metals are prevalent in the environment, so people are exposed on a daily basis. Normal concentrations are reported, but normal is a reflection of an individual’s environment. People who drink well water, for example, are often susceptible to higher concentrations of various metals, such as arsenic, than those who don’t.

A common misconception is that the testing of hair is equivalent to hair follicle testing. The anatomy of head hair reveals that the follicle encloses the hair root beneath the skin. The dermal papilla is at the base of the follicle and is fed by the bloodstream. Various analytes within the bloodstream enter the growing hair under the skin and ultimately become part of the emerging visible hair. It takes about one week for the analyte-hair complex in head hair to emerge. While all the mechanisms by which analytes get into and stay in hair are not understood, it can be reasonably predicted that metals binding to sulfhydryl groups within the hair is integral to the process.

Another concern with metals analyses in hair is the potential for contamination. Because metals are ubiquitous in our day-to-day environment, it is possible that hair can be contaminated at some point between collection and analysis. All facets of hair analyses, including collection, must be performed carefully to limit the chance of contamination, with subsequent findings interpreted in light of such issues. Further confounding the issue are reports of metals and drugs migrating through hair once in the hair. The concept of analyte mobility in hair is controversial but is included here for completeness purposes. Lastly, hair, once above the skin, may be exposed to various analytes through sweat, sebum, and the environment, thus representing additional sources of positive results in hair.

Robert A. Middleberg, PhD, DABFT, DABCC-TC
Laboratory Director
Vice President of Quality Assurance
National Medical Services Labs
Willow Grove, Pa.

Consultant, CAP Toxicology
Resource Committee

Q. Is it necessary to do a cell count and differential on body fluids/cerebrospinal fluid, or CSF, on tube one and tube four? Our ER physicians insist on doing this with CSF. They are upset we get the same results.

A. Comparing cell counts on the first and last tubes collected from a lumbar puncture is a common practice that is used to help recognize a traumatic tap. Traumatic taps occur in about 20 percent of lumbar punctures. The theory is that traumatic taps will show decreasing numbers of erythrocytes as the sample is collected, providing a clue that allows the clinician to distinguish a traumatic tap from a central nervous system, or CNS, hemorrhage, and interpret the results accordingly. In a traumatic tap, the differential can be affected if the peripheral blood leukocyte population differs significantly from the CSF population. The fact that you are seeing the same results in both tubes is a good finding, suggesting that there is no contamination from the peripheral blood.

There are other clues that one can use to distinguish a traumatic tap from CNS hemorrhage, and many of these are more reliable than comparing cell counts in the first and last tubes. Xanthochromia (which is seen as a color change in the centrifuged supernatant) appears within hours of CNS hemorrhage and can persist for up to four weeks. Erythrophages will also appear within a few hours of hemorrhage, and hemosiderin can be seen within approximately 48 hours. Hematin and hematoidin crystals usually are seen two weeks or more after the event and can be either within macrophages or neutrophils or lying free.


Galagan KA, Blomberg D, Cornbleet PJ, et al. Color Atlas of Body Fluids. An Illustrated Field Guide Based on Proficiency Testing. Northfield, Ill: College of American Pathologists; 2006:47–49, 148–151, 158–159, 270–275.

Katherine A. Galagan, MD
Chief of Pathology and
Director of Clinical Laboratories
Virginia Mason Medical Center
Seattle, Wash.