Evaluation of commutability of control materials

[Analytical Quality of Glucose Measurements in Germany]

The measurement quality of systems used for determination of glucose concentrations has to be sufficiently high to obtain measurement results that are reliable in a clinical context regarding the intended use (e. g., diabetes diagnosis and monitoring). The "Richtlinie der Bundesärztekammer zur Qualitätssicherung laboratoriumsmedizinischer Untersuchungen" (guideline of the German Medical Association on quality assurance in medical laboratory examinations) includes specifications on the internal and external quality assurance that are legally binding for glucose measurements in healthcare. In the opinion of the authors, however, there is room for improvement, and examples are provided. Systems for self-monitoring of blood glucose by patients do not fall under any legally binding requirements for quality assurance. With systems for continuous glucose monitoring, there are currently no technological means to regularly check measurement quality. Additionally, repeated manufacturer-independent evaluations, which could lead to improved measurement quality, are not available.

Commutability of a Whole-Blood External Quality Assessment Material for Point-of-Care C-Reactive Protein, Glucose, and Hemoglobin Testing

BACKGROUND

The optimal situation in external quality assessment (EQA) is to use commutable materials. No previous study has examined the commutability of a whole-blood material for point-of-care (POC) testing. The aim of this study was to determine the commutability of the Norwegian Quality Improvement of Laboratory Examinations (Noklus) organization's “in-house” whole-blood EQA material for C-reactive protein (CRP), glucose, and hemoglobin for frequently used POC instruments in Norway and to determine the possibility of using a common target value for each analyte.

METHODS

The study was performed according to the Clinical and Laboratory Standards Institute guidelines. The EQA material was pooled stabilized EDTA venous whole-blood containing different concentrations of the analytes. The EQA material and native routine patient samples were analyzed using 17 POC and 3 hospital instruments. The commutability was assessed using Deming regression analysis with 95% prediction intervals for each instrument comparison.

RESULTS

The EQA material was commutable for all CRP and hemoglobin POC instruments, whereas for glucose the material was commutable for all POC instruments at the lowest concentration analyzed [126.0 mg/dL (7.0 mmol/L)] and for 3 POC instruments at all of the concentrations analyzed.

CONCLUSIONS

Noklus EQA participants using CRP and hemoglobin POC instruments now receive results that are compared with a reference target value, whereas the results for participants using glucose POC instruments are still compared with method-specific target values. Systematic deviations from a reference target value for the commutable glucose POC instruments can be calculated, and this additional information can now be offered to these participants and to the manufacturers.

Trueness assessment for serum glucose measurement using commercial systems through the preparation of commutable reference materials

BACKGROUND

Commutable reference materials (RMs) are suitable for end-users for evaluating the metrological traceability of values obtained using routine measurement systems. We assessed the performance of 6 routine measurement systems with validated secondary RMs.

METHODS

We tested the homogeneity, stability, and commutability of 5 minimally processed human serum pools according to the standard guidelines. The serum pools were assigned values as per the reference procedure of the United States Centers for Disease Control and were used to evaluate the trueness of results from 6 commercial measurement systems based on enzymatic methods: 3 glucose oxidase (GOD) and 3 hexokinase (HK) methods.

RESULTS

The prepared RMs were validated to be sufficiently homogenous, stable, and commutable with the patient samples. Method bias varied for different systems: GOD01, -0.17 to 2.88%; GOD02, 1.66 to 4.58%; GOD03, -0.17 to 3.14%; HK01, -3.48 to -0.85%; HK02, -3.83 to -0.11%, and HK03, -1.82 to -0.27%.

CONCLUSIONS

We observed that the prepared serum glucose RMs were qualified for trueness assessment. Most of the measurement systems met the minimal quality specifications.

The commutability of external quality assurance serum and reference serum materials between the VITROS® Albumin Slide and four other routine albumin methods

Background

Between-method differences in external quality assurance schemes (EQAS) are assumed to be indicative of between-method differences in results for fresh diagnostic serum samples. However, this assumption is only valid if the EQAS fluid is shown to be commutable between methods with the fresh human samples. Using fresh human serum samples, we studied the commutability of six UK National EQAS (UKNEQAS) samples and two reference serum preparations using five methods for the measurement of albumin.

Methods

The VITROS® Albumin Slide was compared with two liquid reagent bromocresol green-based methods and two immunoturbidimetric methods. Thirty fresh human serum samples, six UKNEQAS samples and two reference materials were analysed over a period of five days by all methods. The reference materials were: a certified protein reference material, CRM470 (protein reference preparation) and the Scandinavian NFKK Reference Serum X.

Results

A concentration-dependent tendency towards non-commutability was seen for the six UKNEQAS samples. Two of the methods recovered the CRM470 above the upper limit of the expected range and the remaining three were within the expected range.

Conclusions

Assessment of commutability is important in the investigation of between-method differences in EQAS. External quality assurance and reference materials should have been demonstrated to be commutable and be available at multiple concentrations, before they may be considered appropriate for the assessment of accuracy.