PubMed · 5806441
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J W Ten Cate. 1969. Acquired platelet defects.. https://pubmed.ncbi.nlm.nih.gov/5806441/
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Coagulometer-induced errors in International Normalized Ratios (INR) may be corrected by assigning an International Sensitivity Index (ISI) specific for the local combination of coagulometer and thromboplastin reagent (System ISI). In the present study, 57 laboratories determined the INR of eight frozen coumarin plasmas. There was considerable variation in INR reported at the different centres, with coefficients of variation (CV) ranging from 11.30% to 17.29%. In addition, their consensus mean INR values were consistently higher than those obtained manually. The overall mean percentage deviation was 20.06%, indicating that correction was required to reduce the over-estimation of INR that occurred even in those Systems incorporating a thromboplastin reagent with an instrument-specific ISI. Local correction using coumarin plasma calibrants reduced this value to < or = 7% with current reference thromboplastins BCT 441, OBT 79 and RBT 90 and also lowered the CV to < 5%. In contrast, when adsorbed plasma calibrants were employed, mean percentage deviations were 7.87% with BCT 441, 12.47% with OBT 79 and 77.37% with RBT 90 as reference respectively. This difference may be due, in part, to the difficulty in assigning an INR to adsorbed plasma calibrants, which contain no protein induced by vitamin K antagonists (PIVKA). This study demonstrates that coumarin plasma calibrants are superior in System ISI calibration.
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The possible applications of the measurement of platelet aggregation by conventional photometry are limited by the short lifetime of platelet suspensions. Recently a microplate-based technique was introduced, which promised to revolutionize experimental design by enabling simultaneous assessment of 96 platelet samples. However, adoption of this technique has been slow since the available equipment was not able to satisfy all the conditions required for conventional aggregometry, especially adequate agitation of samples whilst maintaining total control of incubation temperature. This report describes how these problems may be overcome, together with the introduction of on-line analysis of data using commercially available software, obviating the complexities of data management previously encountered.