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No. 50 (PH 16)
Calculation of Measurement Uncertainty for Complete Blood Cell Counts (CBC)
Atsushi Shirakami, Masako Koguchi, Tsutomu Kakuyama, Kanako Kiso, Takashi Kitagawa
Sysmex Corporation, Japan
Recently, due to penetration of ISO standards (ISO 15189 1) ) and globalization of health services,
medical laboratories are required to assure the reliability of testing results by showing its traceability
and measurement uncertainty. To achieve it, ISO 17511 2) requires IVD manufacturers to establish the
metrological traceability for the testing parameters to the end-users. For hematological testing
parameters, such as CBC, there is no certified reference material (CRM) except for Hb – fresh blood
sample is the only material that can transfer the data of the reference measurement procedure (RMP),
which made the standardization of CBC results more difficult than clinical chemistry. We established the
metrological traceability and the calculation methods of measurement uncertainty for the CBC 5
parameters, WBC, RBC, Hb, Ht and Plt, based on the GUM 3) approach. The major data-transfer process
in the manufacturer consists of the following three steps ;
Step 1. Value assignment of five fresh blood samples with RMP
Step 2. Calibration of standard analyzers with value-assigned fresh blood samples
Step 3. Value assignment of product calibrator
For each step, we evaluated the major uncertainty sources and calculated the measurement uncertainty
by ANOVA and uncertainty budget. Then we assigned the values of the product calibrator with
expanded uncertainty (coverage factor; k=2).So medical laboratory can assure the traceability and
measurement uncertainty by calibrating the hematology analyzer with the product calibrator. However,
as for utility of uncertainty in the routine laboratory test results for clinician, more discussion is
necessary.
1)
ISO 15189, Medical laboratories – Particular requirements for quality and competence
2)
ISO 17511, In vitro diagnostic medical devices - Measurement of quantities in biological
samples - Metrological traceability of values assigned to calibrators and control materials
3)
GUM : Guide to the Expression of Uncertainty in Measurement
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