Aim: Biotin in human serum is a potential interfering factor for streptavidin-biotin-based assays. We aimed to evaluate the effective half-life of biotin and biotin metabolites, and establish a pharmacokinetic (PK) model to simulate the time taken for the biotin concentration to fall below a series of thresholds. Materials & methods: PK properties of biotin (5, 10 and 20 mg daily) were evaluated in healthy participants. Biotin serum concentrations were simulated for high-dose regimens (1 mg daily to 300 mg q.i.d.) using a population PK model. Results: Washout periods required for biotin concentrations to reach thresholds ranging from 10 to 100 ng/ml were successfully simulated. Conclusion: Our simulations provide valuable guidance on biotin washout periods necessary to avoid false assay results. Immunoassays that allow rapid measurement of analytes can be vital for the correct diagnosis of a broad range of diseases [1]. The interaction of streptavidin and biotin has been utilized for the development of robust and highly sensitive immunoassays by many manufacturers (Abbott, Beckman Coulter, Ortho Clinical Diagnostics, Roche Diagnostics, Siemens Healthcare Diagnostics and others). Biotin, a water-soluble vitamin, is a small and stable molecule that can be conjugated to many proteins without significantly affecting their biological activity; this interaction is the strongest known noncovalent binding between a protein and a ligand [2].Exogenous biotin has the potential to interfere with streptavidin-biotin-based assay results. The impact of interference on test results can be the generation of falsely high values, obtained when using a competitive assay design, whereby an excess of biotin in the specimen competes with biotinylated analog for binding sites on streptavidin. Alternatively, when using a sandwich assay design, an excess of biotin in the specimen can displace biotinylated antibodies, which can generate falsely low values [3]. Reports of biotin interference leading to incorrect biochemical diagnoses in both adults and children have been published previously, along with warnings to clinicians and pathologists to interpret unexpected assay results with caution and consider the potential effect of biotin interference before making a diagnosis [4][5][6][7].The normal serum concentration of biotin is very low; published average values range from below 0.1 to 0.8 ng/ml [8,9]. The adequate daily intake of biotin is 30 μg/day [10] and biotin deficiency is rare as the majority of diets contain enough biotin for this to be reached. However, biotin is increasingly being marketed as a lifestyle supplement which is claimed to strengthen hair and nails, despite no scientific confirmation of these benefits [11]. The unregulated, over-the-counter (OTC) product is available in doses ranging from 50 μg found in multivitamin

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BackgroundImmunochromatographic rapid antigen tests (RATs) emerged onto the COVID-19 pandemic testing landscape to aid in the rapid diagnosis of people with suspected SARS-CoV-2 infection. RATs are particularly useful where RT-PCR is not immediately available and symptoms suggestive of a high viral load and infectiousness are assumed. Several lateral flow immunoassays have been authorized for use under EUA and/or the CE mark, presenting varying overall clinical performance data generated by the manufacturer or by independent investigators. To compare the real-world clinical performance of commercially available rapid chromatographic immunoassays intended for the qualitative detection of SARS-CoV-2, we performed a systematic meta-analysis of published data.MethodsWe searched the MEDLINE®, Embase, BIOSIS and Derwent Drug File (ProQuest)for manufacturer-independent prospective clinical performance studies comparing SARS-CoV-2 RATs and RT-PCR assays. Only studies on lateral flow assays not needing a separate reader for retrieving the result were included, if data were available on viral load, patients’ symptom status, sample type, and PCR assay used. For better data comparability, recalculation of the studies’ single performance data confidence intervals using the exact Clopper–Pearson method was applied.ResultsWe could include 19 studies (ten peer-reviewed) presenting detailed clinical performance data on 11,209 samples with 2449 RT-PCR-positives out of study prevalence rates between 1.9–100 % and between 50– 100% symptomatic samples. Four studies directly compared two to three different RATs and 15 studies compared one RAT to RT-PCR. Overall specificity ranged, with one test outlier, between 92.4% (87.4– 95.9) and 100% (99.7–100), and overall clinical sensitivity varied between 28.9% (16.4–44.3) and 98.3% (91.1–99.7), depending on assay, population characteristics, viral load, and symptom status. Sensitivity in high-viral-load samples (cycle threshold ≤25) showed a considerable heterogeneity among the assays ranging from 66.7% to 100%.ConclusionOnly two RATs offered sufficient manufacturer-independent, real-world performance data supporting use for the detection of current SARS-CoV-2 infection in symptomatic or high-viral-load patient populations. Reliable positive predictive values require testing of symptomatic patients or asymptomatic individuals only in case of a high pre-test probability. If RATs are used for screening of asymptomatic cases in low-prevalence scenarios, a lower positive predictive value of the result has to be considered.

ObjectivesResults can vary between different free thyroxine (FT4) assays; global standardization would improve comparability of results between laboratories, allowing development of common clinical decision limits in evidence-based guidelines.ContentWe summarize the path to standardization of FT4 assays, and challenges associated with FT4 testing in special populations, including the need for collaborative efforts toward establishing population-specific reference intervals. The International Federation of Clinical Chemistry and Laboratory Medicine Committee for Standardization of Thyroid Function Tests has undertaken FT4 immunoassay method comparison and recalibration studies and developed a reference measurement procedure that is currently being validated. Further studies are needed to establish common reference intervals/clinical decision limits. Standardization of FT4 assays will change test results substantially; therefore, a major education program will be required to ensure stakeholders are aware of the benefits of FT4 standardization, planned transition procedure, and potential clinical impact of the changes. Assay recalibration by manufacturers and approval process simplification by regulatory authorities will help minimize the clinical impact of standardization.SummarySignificant progress has been made toward standardization of FT4 testing, but technical and logistical challenges remain.OutlookCollaborative efforts by manufacturers, laboratories, and clinicians are required to achieve successful global standardization of the FT4 assays.

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