The lack of standardization of cardiac troponin I assay systems.

The lack of standardization of cardiac troponin I (cTnI) assay systems has meant an inability to compare absolute values between methods, and non-traceability of cTnI measurement in clinical laboratories. The present study tested whether a common calibrator for cTnI would harmonize values between different methods. Twenty fresh-frozen plasma samples and a common calibrator were analyzed in duplicate using the Dade Behring Stratus II, Chiron ACS:180, Abbott AxSYM, and Beckman Coulter Access immunoassay systems. Uncorrected cTnI values varied up to 60-fold between systems, and when correlated to the Stratus, linear regression slopes were 0.97 (ACS:180), 4.86 (AxSYM), and 0.03 (Access), verifying the differences in calibration. After correction for calibration differences by reference to the common calibrator, among-assay CV ranged from 2.7% to 55%, and was >25% for eight samples. However, the exclusion of Access results reduced the CV to 32% with only four outliers. The results show that comparable cTnI values between methods are possible by the use of a common calibrator. The lack of method harmonization for some samples may be due to non-equal antibody immunoreactivity of different plasma cTnI forms. The complete standardization of cTnI measurement requires both a secondary reference material and standardization of manufacturers' cTnI antibodies.

Evaluation of the Accusport Lactate Analyser.

An investigation of the Accusport Lactate Analyser (ACC) was undertaken to assess its accuracy, linearity, reliability, and versatility. Accuracy was determined by comparing 32 blood assays on the ACC with those obtained using the Kodak Ektachem E250 (E250). Linearity was determined over the range 1.2-18.7 mmol/L. Reliability was measured at 1.7 (low) and 14.4 (high) mmol/L concentrations. Versatility involved determining the optimal sample volume, influence of haematocrit, and the effect of time delay from sampling to assay. Assays determined using the ACC confirm good agreement with the E250. The difference between the two methods compared for lactate determination does not exceed 1.1 mmol/L for concentrations up to approximately 20 mmol/L. Linearity is demonstrated by the regression equation y = 0.026 + 0.970x, r = 0.995. Reliability is expressed by the coefficient of variation of 7% (low) and 4.6% (high). The optimal sample size for accurate assay was determined to be between 20 microL and 50 microL. Mean lactate value did not vary significantly between a haematocrit of 35% and 45%. The Accusport is accurate, linear up to at least 18.7 mmol/L, has good reliability at high and low concentrations, and is able to analyse whole blood up to 15 minutes after sample application to the reagent strip.

A simple quality control protocol for haemoximetry using standard p50.

We have designed a quality control tool for haemoximetry using the principle that standard p50, calculated from blood gas and haemoximetry measurements using the Siggaard-Andersen algorithm, remains unchanged when a specimen of venous blood is oxygenated progressively to 97% saturation of haemoglobin. If the haemoximeter is inaccurate, progressively larger deviations of standard p50 from the constant value occur above 80% saturation. Deviations too small to be detected by analysis of quality control materials comprised of non-haemoglobin dyes and yet sufficient to cause significant errors in derived extractivity parameters can be detected by this method. The suggested protocol is easy to perform, and is recommended as a quality control tool for blood gas analyser/haemoximeters used to determine arterial extractivity parameters.