Comparative evaluation of Rosner’s index (ICA) Vs Chang’s (% correction) as a screening test (mixing study)

Introduction: It is difficult to interpretate mixing study results (both screening & confirmatory) in presence of LAC. The main objective of this study is to define cut off values for ICA & % Correction which will reduce the no. of false positive & negative cases & will help in proper categorization of factor deficiency & inhibitors. This study also briefs about preanalytical errors & their correction Material and Methods: Rosner Index= × Cut offs ? 10 = Correction & ? 15 = Inhibitor Latest Sysmex CS-5100 auto-analyser was used to determine the Cut-offs. DRVVT mixing test ratio (Rosners index/ ICA) 1.15, % correction = 10, DRVVT Normalised ratio (NR) = 1.05. p value < 0>15 is 91.1% sensitive for inhibitor diagnosis & it could not categorise, 8% of total cases into factor deficiency /inhibitor. Discussion: Rosners index (ICA) as a confirmatory test for LA is more sensitive than % correction & DRVVT NR. Chang's % correction with a cut off value of >70% is 85% sensitive in diagnosing factor deficiency & a cut off value of <58> Conclusion: It can be safely concluded that Rosner index is better than % correction, both as a screening test & confirmatory test, to differentiate factor deficiency from inhibitor. This study results are in agreement with CLSI guidelines & favours the sequential order screen-confirm- & then if required mixing study as in case of screen and confirm analysis is not clear-cut and/or when other causes of prolonged clotting times are known or suspected The draw back with the mixing studies is that weak LAC can be missed. Though in this study Nijmegen is better than Bethesda in terms of sensitivity & specificity as the later gives false positive results, other studies has to be taken into consideration which shows that both the Bethesda & Nijgmegen technique have low specificity at higher inhibitor titre. If actual quantitation of high titre activity is required, then it is more reliable to estimate empirically plasma dilution that gives 50% inhibition.