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CAP Today




June 2011

The CAP has 30 official liaisons to various organizations who attend scientific meetings or designate others to do so. They report to the Standards Committee, which reports to the Council on Scientific Affairs. We publish periodically bits of what the CAP’s outbound liaisons hear and see in their liaison roles.

Revising ISO 15189: goals and next steps

William J. Castellani, MD

The ISO 15189 standard, Medical Laboratories—Particular Requirements for Quality and Competence, applies quality system requirements to the clinical laboratory with a strong focus on responsiveness to the client’s needs (patient and clinician). Although originally intended to provide structured quality requirements to the clinical laboratory, it is used as an accreditation standard internationally. The current version was published in 2007 and a draft revision is now being considered. The CAP currently supports three liaisons to the work group responsible for the standard (I am one, and John Eckfeldt, MD, PhD, and Christopher Lehman, MD, are the others) and provides input to the U.S. position on this and associated standards. More text has been added in the draft, but most of the material strives to clarify the requirements in the current standard. Nonetheless, areas of controversy remain.

The work group has spent considerable time addressing the concept of uncertainty of measurement in the medical laboratory. In the science of measurement (metrology), the uncertainty associated with any determination is an important consideration: It determines how much confidence should be placed on the determination and, more important, if a product specification gives a range of acceptability, whether the true value is actually likely to fall within this range. This acknowledges that there is error but the measurement is the only guide to the underlying true value. Several standards bodies concerned with metrologic issues, including ISO, have adopted a formal approach called the Guide to the Expression of Uncertainty in Measurement, or GUM. Medical laboratories, however, work in a different environment, one in which measurements are rarely done in isolation. Results are interpreted in the context of a patient with a history, associated findings, and correlative laboratory data. Laboratory results are a limited snapshot view of a dynamic, complex system (the patient) in which other external needs may be in play, especially speed. Results never are absolute: A “normal” result does not prove health, and an “abnormal” result does not document disease.

Given this disparity, two attempts have been made to provide a bridge between the GUM and medical laboratory testing: ISO Draft Technical Specification 25680, Medical Laboratories—Calculation and Expression of Measurement Uncertainty, and CLSI C51-P, Expression of Measurement Uncertainty in Laboratory Medicine; Proposed Guideline, both of which the College has reviewed. The difficulty of this undertaking is clear given there are two documents on the same issue, the ISO document is not a standard but a technical specification (which is more informative, intended to either lead to a standard in the future or be withdrawn after a limited life span), the ISO document went through nine versions before being circulated as the current draft (and has received negative votes), and the CLSI document was prepared while the ISO document was undergoing its gestation. The wording of the draft ISO 15189 revision regarding uncertainty of measurement emphasizes the need to recognize the error in any result and its various sources, and be able to provide to the user—the clinician—a reasonable estimate of this error. The formalism in the GUM must be put in the context of the role of any measurement in evaluating a patient and is anticipated to be a major point in the discussion of this concept as the ISO 15189 revision proceeds.

A committee draft has already been circulated among the member bodies of ISO Technical Committee 212. This draft international standard is now in the comment period, with the expectation that the comments will be addressed at the next Work Group 1 meeting in October. If the document is felt to be ready for publication, it will then circulate as a final draft international standard for approval or disapproval. If approved, it will be scheduled for publication; it becomes the official standard on publication, supplanting the current 2007 version.

Dr. Castellani, vice chair of the CAP Standards Committee, is in the Department of Pathology at Penn State Hershey Medical Center. He is the CAP’s liaison to ISO Technical Committee 212 Work Group 1.