October 2011 Clinical Laboratory News: Biological Variation Overlooked too Often

AM 2011

The educational offerings at the AACC 2011 Annual Meeting were as diverse as the attendees. Symposia, workshops, brown bag sessions, and more gave attendees the latest information, as well as practical advice, on a myriad of clinical lab topics. Below is a brief on one of the sessions.

Biological Variation Overlooked Too Often

By Genna Rollins

Biological variation is an important, but sometimes overlooked, source of test result variation that can be quite significant in putting test results in context, according to Alan Wu, PhD, moderator and one of three panelists for a short course on the subject. “There’s a tendency among clinicians to over-interpret lab values rather than not understanding that lab data has inherent variability,” he said.

A professor of laboratory medicine and chief of the clinical chemistry laboratory at San Francisco General Hospital, Wu explained that intra-individual variation can be used to determine the reference change value, the change needed in an individual’s serial results before the change is considered significant. The Index of Individuality, the ratio of intra- and inter-individuality, is helpful in determining whether traditional population-based reference values have utility for any particular analyte.

For example, when the index of individuality is <0.6, the dispersion of values for an individual will span only a small portion of the reference range, and therefore reference values will be of little utility. Analytes with this type of profile, like creatinine, are best used for monitoring disease trends. In contrast, for analytes with a high index of individuality >1.4, the distribution of values from any individual will cover much of the entire reference range, making conventional reference ranges of greater utility. An example is cystatin C, which is better used for disease diagnosis.

Co-presenters Roy Gerona, PhD, and Martin Kroll, MD, spoke, respectively, on incorporating biological variation in quality control programs, and taking biological variation into consideration when interpreting lab results. Gerona is a research scientist at the University of California San Francisco, and Kroll is chief of laboratory medicine at the Boston University School of Medicine.

Wu mentioned that he relies on Callum Fraser’s book, Biological Variation: From Principles to Practice, which is available through AACC’s online bookstore. Wu said, “it’s the biological variation Bible. I’ve read it multiple times and I’ve gotten something out of it every time.”

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