A national surveillance program for evaluating new reagent lots in medical laboratories.

OBJECTIVES: Differences between laboratory results attributable to the use of different reagent lots can potentially affect the diagnosis and monitoring of patients. To minimize patient risks, all laboratories should verify that new reagent lots meet agreed analytical performance specifications (APS). We propose a simplified, pragmatic approach for laboratories that involves compilating results into a national surveillance program, and present the first results obtained when applying this approach to troponins, glycated hemoglobin (HbA1c), prostate-specific antigen (PSA) and D-dimer. METHODS: In the surveillance program we have (i) determined APS for selected analytes, (ii) implemented a simplified procedure for lot evaluation with patient samples used in laboratories across Norway and (iii) performed central processing of the results from the participating laboratories. RESULTS: Over a one-year period, 27 Norwegian laboratories returned results from 28 lot changes for troponin I, 11 for troponin T, and 29 for HbA1c, PSA and D-dimer. The mean difference between two reagent lots was 4.5% for troponin I (for a concentration interval of 20-32 ng/L), 5.1% for troponin T (10.7-17.5 ng/L), 2.2% for HbA1c (40-50 mmol/mol), 3.7% for PSA (3-5 µg/L) and 5.5% for D-dimer (0.4-1.0 mg/L FEU). CONCLUSIONS: A novel procedure for reagent lot evaluation is proposed in which information about multiple lot changes from different medical laboratories can be accumulated nationally. Sharing this information allows simplification of lot evaluations in individual laboratories and provides real-world data about lot-to-lot variations.

Self-management of warfarin therapy.

BACKGROUND: Clinical studies from other countries show that self-management of warfarin therapy may reduce the risk of mortality, thromboembolism and complications when compared to conventional therapy. The purpose of this study was to train patients in self-management and compare the results with conventional therapy in Norway. METHOD: A total of 23 patients who had previously been given conventional therapy by their GPs were instructed in how to measure INR (using the CoaguChek XS device) and administer warfarin dosage through a structured training programme over the course of 27 weeks. The participants continued with self-management for a further 28 weeks after the end of the training period. The time in the therapeutic range (TTR, measured as a percentage) was calculated and the TTR for conventional therapy and self-management were compared. RESULTS: No significant difference in average TTR was found when comparing conventional therapy (70% (95% confidence interval (CI) 62-78)) with the self-management period (75% (95% CI 69-81, p = 0.24)). The percentage of extreme INR values (< 1.5 or > 5.0) was higher during conventional therapy than during self-management (6.8% vs. 1.0%, p < 0.001). INTERPRETATION: No significant difference in TTR was found when comparing self-management and conventional warfarin therapy in our study, but for self-management there was a lower percentage of extreme INR values compared to conventional warfarin therapy.

Effect of coagulation factors on discrepancies in International Normalized Ratio results between instruments.

BACKGROUND: The reasons for discrepancies between International Normalized Ratio (INR) results determined by point-of-care-instruments and laboratory measurements are not fully understood. In this study we investigated whether different levels of coagulation factors in the plasma of patients can explain some of the systematic and/or random parts of the difference in INR between the instruments. METHODS: Blood samples were collected at four different patient visits from each of 34 outpatients on warfarin treatment. INR was determined on a laboratory instrument (STA Compact(®)) and on three point-of-care instruments (Simple Simon(®)PT, CoaguChek(®)XS and INRatio™). In addition, the level of fibrinogen, coagulation factors II, V, VII and X was determined. INR instruments were compared in pairs. Simple linear regressions as well as multiple linear regressions and nested ANOVA analyses were used to examine the data. RESULTS: The coagulation factors, especially fibrinogen, factors II and VII, could explain between 16% and 45% of the total variance of the differences in INR between instruments dependent on instruments compared. After correction for factors no systematic difference was seen for four of the six comparisons and the between- and within-subject variation of the differences were reduced by up to 69% and 52%, respectively. CONCLUSIONS: By correcting for the appropriate coagulation factors, especially the systematic differences, but also the between- and within-subject variation of the differences between instruments, were reduced. This indicates that different levels of coagulation factors in the plasma of the patients play an important role in explaining discrepancies between INR instruments.