The initial reporter received a questionable elecsys tsh assay result for one patient with the cobas e 801 module serial number (b)(4).Historically, the patient's tsh ran around 1 miu/ml with a normal ft4.Then in (b)(6) 2019, the patient's tsh was 95 miu/ml.A similar result was obtained in (b)(6) 2020.On (b)(6)2020 the initial result was 63.4 miu/ml.The sample was tested with a 1:2 dilution with a result of 64.6 miu/ml.The sample was tested with a 1:5 dilution with a result of 53.4 miu/ml.The sample was tested with precipitation with scantibody tubes and the result was negative and polyethylglycol treatment was negative.Due to scantibody, the customer does not believe the high results are due to macro-tsh.The sample was also processed on a liaison analyzer with a result of 0.65 miu/ml.The questionable result was reported outside the laboratory and questioned by the endocrinologist.
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The patient sample was provided for investigation.Upon initial investigation, the results obtained by the customer could be reproduced.Further investigations of the sample determined that it contains an interfering factor against the f(ab')2 fragment of the assay antibody as well as the ruthenium label of the assay.Per product labeling: "in rare cases, interference due to extremely high titers of antibodies to analyte-specific antibodies, streptavidin or ruthenium can occur.These effects are minimized by suitable test design.".
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