Wayne, Pennsylvania, USA-The Clinical and
Laboratory Standards Institute (CLSI) recently published Expression of
Measurement Uncertainty in Laboratory Medicine; Approved Guideline (C51-A).
This document describes a practical approach to assist clinical laboratories
and in vitro diagnostic device manufacturers in developing and calculating
useful estimates of measurement uncertainty, and illustrates their application
in maintaining and improving the quality of measured values used in patient
C51 illustrates the assessment of measurement uncertainty
with both bottom-up and top-down approaches. The bottom-up approach suggests
that all possible sources of uncertainty are identified and quantified in an
uncertainty budget. A combined uncertainty is calculated using statistical
propagation rules. The top-down approach directly estimates the measurement
uncertainty results produced by a measuring system. Methods to estimate the
imprecision and bias are presented theoretically and in worked examples.
“Uncertainty is the modern way to describe the
relevance of a result of measurement,” states Anders Kallner, MD, PhD,
Associate Professor of Clinical Chemistry, Karolinska
Hospital, Stockholm, Sweden,
and Chairholder of the document development committee. “This document
describes the concept and how it can be used in practice in an easy and
The guideline discusses the definition of what is intended
to be measured, lists sources of measurement uncertainty, describes the
generation of statistical estimates of uncertainties and their combination, and
discusses the use of uncertainty estimates.
The objectives of this document are to:
- Familiarize the reader with the concept of measurement
- Describe the processes of implementing the concept of
measurement uncertainty in laboratory medicine.
- Describe the practical approaches to developing relevant and
useful estimates of measurement uncertainty.
- Discuss the uses of the measurement uncertainty information
“Measurement uncertainty is a relatively recent, but
essential concept for comparing measurements across time and place,”
explains David L. Duewer, PhD, Analytical Chemistry Division, National
Institute of Standards and Technology, and a member of the document development
committee. “The document, championed and guided by the late Richard R.
Miller, Jr., seeks to help the clinical chemistry communities better
understand, make use of, and estimate measurement uncertainty.”
The principles for expression of measurement uncertainty
provided in the document illustrate how the components of measurement
uncertainty can be combined to help estimate the performance characteristics
that can be reliably achieved by the measuring system. The recommendations
provided are consistent with the Guide to the expression of uncertainty in
measurement (GUM) and with the International Organization for Standardization
(ISO) standards concerned with laboratory accreditation.
CLSI and the Association of Public Health Laboratories
(APHL) have announced a related webinar to this document. The webinar,
Uncertainty in Measurements – Estimation and Practical Use, will take place on
April 5, 2012 from 1:00 PM to 2:00 PM Eastern (US) Time. Dr. Kallner, the
aforementioned Chairholder of the C51 document development committee and the
speaker for this webinar, will discuss how uncertainty in measurement is
internationally established in all fields of analytical chemistry, physics, and
CLSI is a volunteer-driven, membership-supported, nonprofit
organization dedicated to developing standards and guidelines for the health
care and medical testing community through a consensus process that balances
the perspectives of industry, government, and the health care professions. For
additional information, visit the CLSI website at www.clsi.org
or call 610.688.0100.