Johnston M, Harrison L, Moffat K, Willan A, Hirsh J
Hamilton Civic Hospitals Research Centre, Ontario, Canada.
J Lab Clin Med. 1996 Aug;128(2):214-7. doi: 10.1016/s0022-2143(96)90014-1.
The International Normalized Ratio (INR) was introduced to reduce the variability of prothrombin time (PT) reporting. One potential problem with the use of the INR is the assumption that its reliability is reduced when it is used to monitor patients during the induction phase of treatment. This shortcoming arises because the model used to establish the INR system is based on the use of pooled plasma from patients stabilized on warfarin for at least 6 weeks. Because the prolongation of the PT by warfarin during the induction phase mainly reflects reduction in factor VII levels (whereas the prolongation of the PT after 6 weeks of stabilization reflects reductions in factors X, II, and VII), there exists a potential for loss of accuracy of the INR during warfarin induction. To overcome this potential problem, it has been suggested that the PT ratio should be used to report results during the induction phase of treatment and that the INR system should be reserved for reporting results after the patient has been stabilized. This approach is confusing to the clinician. In addition, the validity of this approach has never been demonstrated in a clinical study. To address this issue, we studied 43 patients for the first 5 days after they started warfarin therapy. We measured the PT in the same plasma samples from each patient with five different commercial thromboplastins. The variance in the PT ratios among the five thromboplastins was compared with the variance obtained with the INR values derived from the PT ratios when using the international sensitivity indexes provided by the manufacturer. Our results indicate that, even during the induction phase, there is less variance with the INR system than with the PT ratio system.
国际标准化比值（INR）的引入是为了减少凝血酶原时间（PT）报告的变异性。使用INR的一个潜在问题是，人们认为在治疗诱导期用于监测患者时，其可靠性会降低。出现这一缺点的原因是，用于建立INR系统的模型是基于使用华法林稳定治疗至少6周的患者的混合血浆。因为华法林在诱导期使PT延长主要反映因子VII水平降低（而稳定治疗6周后PT延长反映因子X、II和VII降低），所以在华法林诱导期间存在INR准确性丧失的可能性。为克服这一潜在问题，有人建议在治疗诱导期应使用PT比值报告结果，而INR系统应留作患者病情稳定后报告结果之用。这种方法让临床医生感到困惑。此外，这种方法的有效性从未在临床研究中得到证实。为解决这一问题，我们对43例开始华法林治疗后的前5天的患者进行了研究。我们用五种不同的商用凝血活酶在每个患者的相同血浆样本中测量PT。将五种凝血活酶之间PT比值的方差与使用制造商提供的国际敏感指数从PT比值得出的INR值的方差进行比较。我们的结果表明，即使在诱导期，INR系统的方差也比PT比值系统的方差小。
