Verification of the analytical characteristics of troponin assays in the laboratory : A how to guide

It is important that both laboratory staff performing troponin measurement and clinicians who interpret troponin results should 'know their routine laboratory's troponin assay' and its performance characteristics. International quality systems established by the International Organization for Standardization (ISO) and accepted by clinical laboratories worldwide require the verification of a new method. As a minimum, a troponin method must be verified as showing 'fitness for purpose' before being used to produce analytical data for patient care. The analytical performance characteristics of troponin assays that require an initial verification include imprecision and limit of quantitation. Validation of the upper reference limit that has been established by the manufacturer is also highly desirable, if possible. If the assay is replacing a previous assay, a method comparison and, if possible, an audit of performance should also be done. Investigation of other characteristics such as limit of blank, limit of detection, interferences and linearity is optional and depends on a laboratory's situation and the availability of resources to do this work. The monitoring of assay performance requires use of appropriate Intemal Quality Controls to assess the assay traceability (bias) and imprecision, and participation in an External Quality Assessinent Scheme to evaluate the assay accuracy and laboratory performance. In addition, the introduction of newer more sensitive troponin assays may require clinical validation in collaboration with local cardiology units and emergency medicine departments, and auditing of the impact of implementation of these more analytically sensitive assays. The following chapter provides a 'how to' guide to clinical laboratories for the verification and monitoring of the analytical performance of troponin assays.