Introduction: SARS-CoV-2 antigen tests can complement and substitute for RT-PCR tests. Centralized laboratory automated SARS-CoV-2 antigen tests that can be scaled to process a large number COVID-19 cases simultaneously are now available. We have evaluated the new Roche Elecsys SARS-CoV-2 antigen electro-chemiluminescent immunoassay. Methods: The Roche SARS-CoV-2 antigen assay is a double-antibody sandwich electro-chemiluminescent immunoassay, which reports a cut-off index (COI) (COI ≥ 1.0 considered positive). We assessed assay precision and linearity, and confirmed the reactivity limit. We determined the assay sensitivity and specificity with a verification group (289 controls and 61 RT-PCR positive COVID-19 cases). Assay performance was also validated against the consecutive samples we received (7657 controls and 17 cases) for SARS-CoV-2 antigen testing from June to October 2021. Result: The assay had a within-run precision CV of 3.0% at COI 0.68, and a CV of 1.5% at COI 3.49. Between-run precision was 3.0% at COI 0.68 and 1.8% at COI 3.49. The assay was linear from COI 0.65 to 7.84. All 35 C50 ± 20% test results performed over 7 days were positive/negative, respectively. In the verification group, overall sensitivity was 42.6% (26/61 positive, 95% CI 30.0–55.9), and specificity was 99.7% (1/289 positive, 95% CI 98.1–100). The agreement between the SARS-CoV-2 antigen and the RT-PCR cycle threshold (Ct) count was good (r = 0.90). In cases with Ct counts ≤ 30, the antigen assay sensitivity improved to 94.7% (18/19 positive, 95% CI 74.0–99.9). In our validation group, antigen sensitivity was 62.5% (5/8 antigen positive, 95% CI 24.5–91.5) within the first week of disease onset, but no cases were reactive after the first week of disease onset. Conclusion: The Elecsys SARS-CoV-2 antigen assay has good performance within manufacturer specifications. The sensitivity of the Roche antigen assay was greatest when used in patients with lower RT-PCR Ct values (≤30) and within the first week of disease onset.
Background The anion gap (AG) is often used to evaluate acid–base disorders. The reference interval for normal AG is used to differentiate between raised (gap) or normal AG (non‐gap) acidosis. Historically accepted AG values may not be valid with the evolution of modern analytical techniques and the reference interval requires revalidation. Aims To determine the reference interval for AG based on current laboratory techniques. Methods During a health‐screening exercise, 284 participants with no major illnesses volunteered surplus blood for analysis. The samples were tested in an internationally accredited clinical laboratory. AG was calculated by [Na+] − [Cl−] − [HCO3−] and AGK by [Na+] + [K+] − [Cl−] − [HCO3−]. The reference interval was determined at 2.5th–97.5th percentiles. Analysis was further undertaken for a subcohort of 156 individuals with no suboptimal health indicators. Results Median age was 35 years, body mass index 23.4 kg/m2 and the glomerular filtration rate was 106 mL/min/1.73 m2. Median AG was 13 mmol/L and the reference interval for normal AG is 10–18 mmol/L with a 99% level of confidence. Statistically significant differences in AG were detected for sex, race, obesity and serum albumin, but the difference was 1 mmol/L between subgroups. The reference interval was the same for the sub‐cohort of 156 individuals. Median AGK was 17.7 mmol/L and reference interval was 14.6–22.5 mmol/L. Conclusions The AG reference interval of 10–18 mmol/L is valid for laboratories with similar reference intervals for electrolytes. Lower values expected with current laboratory techniques were not observed. The median AG of 13 mmol/L may be used to differentiate gap acidosis, non‐gap acidosis or mixed acid–base disorders.
Introduction The Roche Cobas c513 (c513) is a dedicated stand-alone high throughput HbA1c analyzer. We evaluated the performance and the difference in turnaround times (TAT) of the c513 against our Cobas 8000 c502 (c502). Methods We assessed the linearity and precision of the c513, and its agreement (Deming regression and Bland–Altman analysis) with the c502 assay. We compared TAT for these analyzers for a single run of 50 samples and for all samples run over 2 comparable time periods. Results The c513 assay was linear from 4.4–18.3% HbA1c. Interassay precision (CV%) was 1.2 and 0.8 at HbA1c levels of 5.7 and 10.5%, respectively. The c513 assay showed excellent concordance with the c502 assay (r = 0.997) with no significant difference between methods by Bland–Altman analysis (mean difference = 0.021% HbA1c, P = 0.1422). The c513 took 17 min to analyze 50 samples, compared to 40 min on the c502. Over comparable 2-month periods, 90% of samples requiring HbA1c tests only were completed under 25 min (c513) vs 30–35 min (c502). For tubes sharing complete blood count (CBC) testing with HbA1c, the 90th percentile TAT was 35–40 min (c513) compared to 45–50 min (c502). Conclusion The c513 assay performs well with excellent correlation to the c502 assay. The improved TAT of the c513 is suitable when there are demands for rapid HbA1c results and it may forestall requests for point-of-care testing. It is also attractive to sites with heavy workloads with a claimed throughput of 400 tests / h.
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