Evaluating Commutability of Control Materials in Three Nordic External Quality Assessment Schemes for Lipoproteins

BACKGROUND

The quality of control materials is crucial for evaluating external quality assessment (EQA) results. To detect method differences, the EQA material should behave the same as a patient sample, meaning the material must be commutable. Noncommutable materials may cause misinterpretations of EQA results. Here, we examined the commutability of EQA materials used in 3 Nordic EQA schemes for lipids.

METHODS

The study was designed according to the procedures recommended for assessing commutability by the International Federation of Clinical Chemistry and Laboratory Medicine. Commutability was assessed based on the difference in bias between a control material (CM) and clinical samples (CS) consisting of human plasma using 2 different measurement procedures (MPs). Measurands: LDL-cholesterol (LDL-C), total cholesterol (TC), HDL-cholesterol (HDL-C), and triglycerides (TG). Four CMs (CM1-4) were assessed for commutability by using 40 CSs and 3 MPs (Abbott Architect, Roche Cobas, and Siemens Atellica).

RESULTS

Unmodified native CMs (CM1 and CM3), stored at -80 °C, were commutable for all included measurands, except for LDL-C that was indeterminate, when comparing MPs pairwise. Modified CM2 was noncommutable for HDL-C, LDL-C, non-HDL-C, and LDL-C calculations. Unmodified native CM4, stored at -20°C were noncommutable for LDL-C.

CONCLUSIONS

Unmodified serum samples stored at -80 °C were commutable for lipids on the evaluated MPs, and therefore suitable as CMs in EQA schemes. Moreover, the study demonstrated that minor modifications of samples may lead to noncommutability.

Quantitative determination of cerebrospinal fluid bilirubin on a high throughput chemistry analyzer

BACKGROUND

Subarachnoid hemorrhage is a condition with high rates of mortality and morbidity. The diagnosis requires an urgent cerebral computed tomography scan and also a lumbar puncture if the scan fails to demonstrate intracranial blood. In Sweden the cerebrospinal fluid (CSF) is analyzed by spectrophotometric scanning for the presence of hemoglobin and bilirubin. The aim of the study was to develop a quantitative diazo reagent based analysis of cerebrospinal fluid bilirubin as a replacement for spectrophotometric scanning.

METHODS

The CSF bilirubin assay on an Architect C8000 chemistry analyzer was compared with spectrophotometry using patient samples.

RESULTS

The method correlates with spectrophotometry, has a good linearity and precision.

CONCLUSIONS

Quantitative bilirubin measurement offers shorter turnaround times, simplifies the interpretation of the results and reduces work load in comparison with spectrophotometry.