The initial reporter received questionable elecsys total psa immunoassay (tpsa) results, for 2 samples, from the cobas 8000 e 801 module serial number (b)(4).This mdr will cover the tpsa reagent.Refer to the mdr with patient identifier = (b)(6) for the elecsys free psa immunoassay (fpsa) reagent.Sample 1: (e801 module results): tpsa: 0.150 ng/ml, fpsa: 2.39 ng/ml.(clia method results): tpsa: 1.17 ng/ml, fpsa: 0.05 ng/ml.Sample 2: (collected on (b)(6) 2019, e801 module results): tpsa: 0.198 ng/ml, fpsa: 3.08 ng/ml.The questionable results were not reported outside the laboratory.
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The patient samples were provided for investigation.Investigations of the patient sample could reproduce the customer's measurements.Further investigations of the sample determined there is evidence of an interfering substance or substances present in the sample, causing a considerable decrease in the recovery of total psa.An anti-psa antibody with different specificity was added to the sample and this showed a significant increase in total psa concentration.This would also suggest the presence of a psa isoform that cannot be completely detected by the usage of the standard elecsys total psa assay.Product labeling for total psa states: " 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.It is known that in rare cases psa isoforms do exist which may be measured differently by different psa tests.Findings of this kind have occasionally been reported for psa tests from various manufacturers.".
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