Commutability Study

Commutability Study of Creatinine Reference Materials

In 2006, NKDEP's Laboratory Working Group (LWG) conducted a commutability study of the National Institute of Standards and Technology's (NIST) Standard Reference Material (SRM) 967 to ensure its commutability with native serum samples for most of the commonly used commercial creatinine methods available at that time.

Reference materials are typically used to establish or validate the calibration traceability of a routine measurement procedure to a reference measurement procedure of higher order. When a reference material is intended to be measured by a routine clinical method, commutability* of the reference material must be validated for all routine methods for which the reference material is intended for use.¹

Results

Fresh, frozen serum creatinine reference materials from NIST, SRM 967 (as well as material from the College of American Pathologists' Accuracy Calibration Verification/Linearity Survey LN24 used in 2006) were found to be commutable with a panel of native clinical serum samples for the manufacturers' reagents and instruments listed below. Reference materials and clinical samples were measured by each of the stated analytical systems and by a LC/IDMS reference measurement procedure at NIST. Commutability was evaluated using criteria described in Clinical and Laboratory Standards Institute (CLSI) document EP14-A2.²

Commutable Reagents and Instruments

Manufacturer	Reagent (Product Number)	Instrument Model
Abbott Diagnostics	Creatinine (7D64)	Abbott AEROSET® System Abbott Diagnostics Creatinine, Next Generation (3L81) Abbott ARCHITECT cSystemsTM c8000
Abbott Diagnostics	Creatinine (7D64)	Abbott ARCHITECT cSystemsTM c8000
Abbott Diagnostics	Creatinine, Next Generation (3L81)	Abbott AEROSET® System
Beckman Coulter, Inc.	CREA (442760)	Synchron® CX4 PRO
Beckman Coulter, Inc.	CREA (442760)	Synchron® Unicel DxC 800
Beckman Coulter, Inc.	Creatinine (443340)	Synchron® CX3 Clinical System
Beckman Coulter, Inc.	CREm (472525)	Synchron® Unicel DxC 800
Dade Behring, Inc.	Dimension® CREA Flex (DF33A)	Dimension® RxL System
Olympus Diagnostics Systems	Creatinine (OSR6178)	Olympus AU400®
Olympus Diagnostics Systems	Creatinine (OSR6178)	Olympus AU640e®
Ortho Clinical Diagnostics	CREA Slides (814 1947)	VITROS® 950 Chemistry System
Roche Diagnostic Corporation	CREA plus (11775642)	Hitachi 911 Analyzer
Roche Diagnostic Corporation	CREA/RB (12217333)	Hitachi 911 Analyzer
Siemens Diagnostics	Creatinine_2 (B01-4126-01)	ADVIA® 1650 Chemistry
Siemens Diagnostics	Creatinine Enzymatic (B01-4127-01)	ADVIA® 1650 Chemistry

The list provided above documents commutability of the NIST SRM 967 and CAP LN24 creatinine reference materials with native clinical serum samples for various reagent-instrument combinations determined for specific reagents used on these specific instrument systems in 2006. The commutability characteristics observed at that time may not apply to different reagent-instrument combinations.

Because the specified creatinine reference materials (NIST SRM 967 and CAP LN24) met the CLSI EP14-A2 criteria for commutability with all reagent-instrument combinations tested, it is expected that these reference materials will be commutable with native clinical serum samples when the same reagent (using the same methodological principle) is used on very similar instrument models supplied by the same instrument manufacturer.

Nevertheless, caution should be exercised in extrapolating the above findings to different reagent-instrument combinations, even when the instruments and reagents are produced by the same in vitro diagnostic manufacturer. It is recommended that clinical laboratories consult with the manufacturer(s) of their reagents and instruments to determine the applicability of the established commutability characteristics for these reference materials to particular measurement procedures, including different configurations of creatinine reagents and instrument models.

*Definition of Commutability

Commutability has been defined as the equivalence of the mathematical relationships between the results of different measurement procedures for a reference material and for representative samples from healthy and diseased individuals.³ This definition is based on the more technical definition in ISO document 17511.⁴ Commutability does not imply accuracy or trueness of results, only that results for a reference material had the same mathematical relationship between two methods that was observed for native clinical samples measured by the same two methods.¹

References

1. CLSI Document C53-A. Characterization and qualification of commutable reference materials for laboratory medicine; approved guideline. Wayne, PA: Clinical and Laboratory Standards Institute; 2010.

2. CLSI Document EP14-A2. Evaluation of Matrix Effects; Approved Guideline. 2nd ed. Wayne, PA: Clinical and Laboratory Standards Institute; 2005.

3. Miller WG, Myers GL, Rej R. Why commutability matters. Clinical Chemistry. 2006;52(4):553–554.

4. ISO International Standard 17511:2003(E). In vitro diagnostic medical devices – Measurement of quantities in biological samples – Metrological traceability of values assigned to calibrators and control materials. 1st ed. Geneva, Switzerland: International Organization for Standards; 2003.