Cutoff Value of Qualitative HBsAg for Confirmatory HBsAg Using the Chemiluminescence Microparticle Immunoassay Method.

BACKGROUND: Confirmatory hepatitis B surface antigen (HBsAg) is an assay used to distinguish weakly reactive from false-positive HBsAg results. OBJECTIVE: To determine the signal to cutoff (S/CO) value of chemiluminescence microparticle immunoassay (CMIA) HBsAg assay that should trigger follow-up confirmatory HBsAg testing. METHODS: All specimens with an initial S/CO value of 0.90-100.00 were subjected to repeat HBsAg testing after high-speed centrifugation. The specimens with an initial S/CO value in that range remained in the same range and were then followed up with confirmatory HBsAg testing. RESULT: In total, 132 specimens had an S/CO value between 0.90 and 100.00 after high-speed centrifugation, followed by confirmatory HBsAg retesting. The S/CO value of HBsAg specimens for which the results required verification with confirmatory HBsAg was 0.98 (100% sensitivity, 3.3% specificity) through 9.32 (47.1% sensitivity, 100% specificity). CONCLUSION: The HBsAg S/CO values (as determined by the chemiluminescent microparticle immunoassay [CMIA] method) that should trigger confirmatory HBsAg testing are 0.98-9.32.

Comparison of point-of-care and central laboratory analyzers for blood gas and lactate measurements.

BACKGROUND: Blood gas analysis and blood lactate measurement have important roles in patient management. Point-of-care (POC) testing simplifies and provides rapid blood gas and lactate measurements. This study aimed to compare pH, pCO2 , pO2 , and lactate measurements between a POC device and a benchtop blood gas analyzer typically used in a hospital central laboratory, and to evaluate the inter-device variability of the POC device. METHODS: A cross-sectional study was conducted with a sample size of 100. Each sample was measured for pH, pCO2 , pO2 , and lactate using a Nova pHOx plus L® benchtop blood gas analyzer in the central laboratory and an i-STAT® handheld POC device. The results of both devices were compared using Pearson or Spearman correlation coefficients and Bland-Altman tests. Testing of the inter-device variability was done by using three different i-STAT® devices, and the results were compared statistically. RESULTS: Strong correlations were observed for all test results. In Bland-Altman analysis, ≥95% of the results were within the limits of agreement, with the exception of lactate, which had only 93%. The results that were beyond the limits were primarily lactate levels >8 mmol/L. Biases between the benchtop analyzer and the i-STAT® were not clinically significant, except pH. No significant inter-device variability was observed between the i-STAT® analyzers. CONCLUSION: This comparison study of pH, pCO2 , pO2 , and lactate measurements between Nova pHOx plus L® and i-STAT® analyzers showed good agreement. However, lactate measurement results >8 mmol/L on the i-STAT® analyzer should be interpreted with caution.