aPTT Mixing Test 의 다양한 판정방법에 대한 비교평가

Abstract

Mixing studies have long been used for the evaluation of an unexplained prolongation of PT and aPTT. If a prolonged PT or aPTT of patiennts plasma(PP) is corrected to normal when mixed with normal pooled plasma(NPP), a factor deficiency is indicated, but if the result is not corrected, a circulating anticoagulant is indicated. The mixing test is a useful frrst line procedure in the performance of the lupus anticoagulant test. The principle of the mixing test is simple, but there is no uniform agreement as to what criteria should be used to judge correction. The retum to normal range after mixing with normal plasma is usually used as a guide for correction. However, it is often inadequate in the cases of a markedly prolonged aPTT with factor deficiency because a prolonged aPTT may not be corrected to normal in a 1: 1 mix of PP with NPP. In those cases, a 4:1 mix of PP with NPP might be more helpful to differentiate the presence of a circulating anticoagulant and factor deficiency. The purpose of this study was to evaluate the four different defmitions of correction for interpreting 1:1 mixing study results for comparison. We have interpreted the mixing test result as ‘corrected’, if the prolonged patient’s result returned to the reference interval. We compared our result with three different kinds of interpretation methods. One of them was a “ plus 5 sec" method which was defined as correction, if the patient’s result after mixing was within the range of plus 5 sec of NPP. The second one was "percent correction" and it was calculated from the formula, including NPP aPTT, patient’ s aPTT and mixing aPTT. For aPTT mixing studies, less than 58 % correction suggested the presence of a circulating anticoagulant. The last one was Rosner index which was calculated from the formula and greater than 15 was regarded as evidence of a circulating anticoagulant. The sensitivity of the four methods was quite similar among four different definitions from 66.7 % to 92.8 %, but "plus 5 sec" methods showed the highest value. The specificity of "percent correction" was 45.2 % and it was the best result. The positive predictive values among four different defmitions were quite similar in the range of 68.2 % - 73.0 %, but negative predictive values were relative lower then the positive predictive values. These results suggested that the mixing test is a useful method to screen the presence of a circulating anticoagulant. In conclusion, our interpretation method showed good sensitivity for detecting circulating anticoagulant, but specificity was relatively poor and the llpercent correctionll method of the aPTT 4: 1 mix testing after incubation is recommended.