Hair Analysis Panel Discussion: Section 6.3
6.3 What Are the Limitations of Hair Analysis?
What Data Gaps and Research Needs Exist?
Throughout the 1½-day meeting, the group identified various factors that currently limit the use of hair analysis in evaluations of environmental exposures. No specific research agenda was proposed, but gaps in the scientific data were clearly identified.4 The limitations and data gaps were recapped by the panelists as follows:
- The lack of standard procedures for sample collection.
- The lack of standardization of methods and quality assurance/quality
control (QA/QC) among laboratories.
- The possible over-interpretation of results far beyond the
current body of scientific data and in light of limitations
of techniques and procedures.
- External contamination from a variety of sources, which
lowers sensitivity (e.g., environmental, hair treatments, personal
hygiene, and others).
- The lack of a body of evidence to demonstrate the effect
of washing hair on analytical results.
- The lack of reference ranges in which to frame the interpretation
of results. Reliable reference ranges are needed—specifically,
background or expected ranges in different geographical areas
or regions. Reference ranges should be applicable to population
of interest. The DiPietro (1989) data are a good start, but
more data characterizing regional differences are needed.
- The lack of data related to uptake/incorporation of environmental
contaminants into hair. For both metals and organic compounds,
neither kinetic models nor metabolite data are known or fully
understood. Identifying metabolites of substances of interest
would be helpful, because they could serve as markers of internal
- The lack of correlation between levels in hair and blood
and other target tissues.
- The lack of an epidemiologic database linking substance-specific hair levels and health end points.
- It was re-emphasized that identifying measurable levels
of particular substance in hair does not mean an adverse effect
will occur or has occurred. From a medical perspective, many
panelists felt strongly that there is little point in performing
hair analysis for a substance if the findings cannot be used
as a diagnostic aid. Justification needs to be provided for
choosing hair analysis over blood or urine analysis, and a connection
to a clinical endpoint is needed.
- A limited knowledge of the biological variations of hair
growth with age, gender, race, and ethnicity.
- Insufficient data on environmentally relevant organic compounds
in hair. However, information on testing for pharmaceuticals
and drugs of abuse may have value for those looking at organic
Panelists repeated, throughout the discussions, the risk communication challenges that exist with any exposure or diagnostic tool. The limits of the state of knowledge need to be communicated as clearly as possible by laboratories, practitioners, ATSDR, etc. (RB, MG).
4 One panelist cited a pre-print of a paper by Jason Ditton, professor of criminology at Sheffield University, England, as a good overview of the potential problems associated with interpreting hair analysis results, which he felt were on par with panel discussions. The paper highlights uncertainties and intra-individual variability in hair growth rates and substance-specific incorporation rates. It also describes the challenges of external contamination issues, including variability in results depending on wash procedures. The paper concludes that hair analysis is not an "absolute dosimeter," but rather a "chronometrically operating relativistic dosimeter" (RB).