ACCURACY AND PRECISION OF THE TAS ANALYZER FOR NEAR-PATIENT INR TESTING BY NON-PATHOLOGY STAFF IN THE COMMUNITY

Aims-To assess the accuracy and precision of INR measurement by traine d practice and district nursing staff using the Thrombolytic tic Asses sment System (TAS) analyser. Methods-Seventeen nurses from four practi ces were trained to measure INR using the TAS analyser on citrated cap illary blood samples. Quality control (QC) consisted of: daily interna l QC using normal and abnormal commercial plasmas; monthly local exter nal QC scheme using fresh citrated venous blood; and registration of a ll analysers in the NEQAS (national external quality assessment scheme ) main users scheme. Results-Analysis of internal QC results demonstra ted satisfactory interanalyser and intra-analyser precision with no ev idence of analytical drift in any of the four practice analysers over an eight month period. Local and national external QC results confirme d the interanalyser precision but INR was underestimated by the TAS an alysers compared with the CA 1000 using either Diagen rabbit brain thr omboplastin or Innovin, and with other NEQAS users. Conclusions-The TA S analyser has many features to commend it for use by non-pathology st aff to determine INR. Local internal and external QC and entry into th e NEQAS main users group are possible because the TAS analyses citrate d plasma or blood. The TAS analyser underestimates INR when the geomet ric mean normal prothrombin time (GMNPT) is determined by conventional methods. A local correction factor can be introduced by adjusting the normal PT to give INR results comparable with the local laboratory. T his is particularly desirable when INRs are measured using both near-p atient and laboratory analytical systems on different occasions.