Missed detection of significant positive and negative shifts in gentamicin assay: implications for routine laboratory...

A product recall was issued for the Roche/Hitachi Cobas Gentamicin II assays on 25^th May 2016 in Australia, after a 15 - 20% positive analytical shift was discovered. Laboratories were advised to employ the Thermo Fisher Gentamicin assay as an alternative. Following the reintroduction of the revised assay on 12^th September 2016, a second reagent recall was made on 20^th March 2017 after the discovery of a 20% negative analytical shift due to erroneous instrument adjustment factor.

The practices of an index laboratory were examined to determine how the analytical shifts evaded detection by routine internal quality control (IQC) and external quality assurance (EQA) systems. The ability of the patient result-based approaches, including moving average (MovAvg) and moving sum of outliers (MovSO) approaches in detecting these shifts were examined.

Internal quality control data of the index laboratory were acceptable prior to the product recall. The practice of adjusting IQC target following a change in assay method resulted in the missed negative shift when the revised Roche assay was reintroduced. While the EQA data of the Roche subgroup showed clear negative bias relative to other laboratory methods, the results were considered as possible 'matrix effect'. The MovAvg method detected the positive shift before the product recall. The MovSO did not detect the negative shift in the index laboratory but did so in another laboratory 5 days before the second product recall.

There are gaps in current laboratory quality practices that leave room for analytical errors to evade detection.