Performance comparison of Westergren modified SRS 100/II and alternate iSED® method for erythrocyte sedimentation rate.

INTRODUCTION: The erythrocyte sedimentation rate (ESR) includes three phases, each prone to different interferences. Due to many disadvantages of the reference Westergren method, modified and alternate methods have been introduced. The aim of this study was to compare the modified Westergren method on SRS 100/II analyzer in citrate blood with the alternate method on iSED® analyzer in EDTA sample. Additionally, possible interfering factors and ESR stability during 6 h at room temperature were evaluated. METHODS: A total of 188 samples were included in the method comparison. Additionally, the effects of inflammation, haematocrit and MCV values on ESR were evaluated. To determine ESR stability in different samples, ESR was evaluated at three time points; within 15 min of blood sampling and after 3 and 6 h in different sample types and analyzers (N = 65). RESULTS: Results indicated the constant difference between tested methods with obtained mean bias of 5 mm (95% CI: 3-7). There was higher absolute mean bias in groups with ESR > 40 mm and elevated inflammation markers (p < 0.001). Regarding different MCV and haematocrit groups there was no statistically significant difference in obtained absolute mean biases for MCV (p = 0.087) while there was higher bias in low haematocrit group compared to normal haematocrit (p = 0.004). In addition, there was a significant difference between ESR values at different time points for iSED® (p < 0.001) and no difference for SRS 100/II analyzer (p = 0.406). CONCLUSION: There are differences in ESR values between tested methods. EDTA sample on iSED® should be analysed as soon as possible to avoid falsely increased ESR.

Faecal calprotectin determination: impact of preanalytical sample treatment and stool consistency on within- and between-method variability.

INTRODUCTION: We assessed the differences in faecal calprotectin (FC) concentrations measured by two assays depending on the stool consistency and extraction method. MATERIALS AND METHODS: Stool samples were extracted using the EliA Stool Extraction Kit, Calex® Cap extraction device and respective weighing methods, while FC concentrations were measured using the EliATM Calprotectin and Bühlmann fCAL® Turbo method and checked for within- and between-method variability with regard to extraction method and stool consistency category. Extraction yield was evaluated for impact of different sample incubation time (10 min and 1 h) in extraction buffer for both methods and for impact of different initial sample dilutions (1:50, 1:100, 1:500) for fCAL® Turbo method. RESULTS: Results determined from Calex® Cap extracts were higher compared to weighing method extracts (mean bias 33.3%; P < 0.001), while no significant difference was found between results obtained with EliA Stool Extraction Kit and weighing method (mean bias 0.1%; P = 0.484), in both cases irrespective of stool consistency. Bühlmann fCAL® Turbo results were higher than EliATM Calprotectin results (mean bias 32.3%, P = 0.025 weighing method; and mean bias 53.9%, P < 0.001 extraction devices), the difference is dependent on stool consistency and FC concentration. Significantly higher FC extraction yield was obtained with longer sample incubation time for both methods (P = 0.019 EliATM Calprotectin; P < 0.001 fCAL® Turbo) and with increasing initial sample dilution for fCAL® Turbo method (P < 0.001). CONCLUSION: Preanalytical stool sample handling proved to be a crucial factor contributing to within- and between-FC assay variability. Standardization is urgently needed in order to assure comparable and reliable FC results.

Gentamicin and Vancomycin Interference on Results of Clinical Chemistry Parameters on Abbott Architect c8000.

CONTEXT.­: Gentamicin and vancomycin are nephrotoxic antibiotics. Little is known about the influence of drug concentrations on results of clinical chemistry tests. OBJECTIVE.­: To investigate gentamicin and vancomycin interference on results of 33 commonly measured biochemistry tests. DESIGN.­: The study was carried out in the University Department of Chemistry, Medical School University Hospital Sestre Milosrdnice (Zagreb, Croatia). For each drug, 10 aliquots of pooled serum were prepared. In order to cover toxic concentrations, pool serum samples were spiked with drugs to obtain 0 to 50 µg/mL of gentamicin and 0 to 200 µg/mL of vancomycin. Biochemistry tests were measured in duplicate on the Architect c8000 analyzer, and drug concentrations were measured on Architect i2000 SR (both Abbott Laboratories, Abbott Park, Illinois). For each tested concentration, bias was calculated against the initial measurement. Acceptance criteria were defined as measurement uncertainty of the commercial control with the value close to the measured range of the pool sample. RESULTS.­: For gentamicin, all bias values were below established criteria. For vancomycin, significant changes were observed for potassium, direct bilirubin, and immunoglobulin A. Significant bias was already detected at low vancomycin concentration (2.98 µg/mL) for direct bilirubin (bias = 9.7%; acceptable = 8%). Potassium bias at the highest vancomycin concentration (204.4 µg/mL) exceeded acceptance criteria (bias = 4.5%; acceptable = 4%). For immunoglobulin A, no apparent trend was observed, and bias is attributed to increased method imprecision. CONCLUSIONS.­: Gentamicin did not interfere with the results of clinical chemistry tests. Direct bilirubin concentration is falsely increased in the presence of vancomycin, and potassium is affected at high concentrations.