Determination of APTT factor sensitivity – the misguiding guideline

Abstract

IntroductionThe Clinical and Laboratory Standards Institute (CLSI) has produced a guideline detailing how to determine the activated partial thromboplastin time’s (APTT) sensitivity to clotting factor deficiencies, by mixing normal and deficient plasmas. Using the guideline, we determined the factor sensitivity of two APTT reagents.MethodsAPTTs were performed using Actin FS and Actin FSL on a Sysmex CS-5100 analyser. The quality of factor-deficient and reference plasmas from three commercial sources was assessed by assaying each of the clotting factors within the plasmas and by performing thrombin generation tests (TGT).ResultsTesting samples from 50 normal healthy subjects gave a two-standard deviation range of 21.8–29.2 s for Actin FS and 23.5–29.3 s for Actin FSL. The upper limits of these ranges were subsequently used to determine APTT factor sensitivity. Assay of factor levels within the deficient plasmas demonstrated that they were specifically deficient in a single factor, with most other factors in the range 50–150 iu/dL (Technoclone factor VII-deficient plasma has 26 iu/dL factor IX). APTTs performed on mixtures of normal and deficient plasmas gave diverse sensitivity to factor deficiencies dependent on the sources of deficient plasma. TGT studies on the deficient plasmas revealed that the potential to generate thrombin was not solely associated with the levels of their component clotting factors.ConclusionDetermination of APTT factor sensitivity in accordance with the CLSI guideline can give inconsistent and misleading results.

Do Pt and APTT Sensitivities to Factors’ Deficiencies Calculated by the H47-A2 2008 CLSI Guideline Reflect the Deficiencies Found in Plasmas from Patient’s?

“…4 This guide procedure was considered as misleading because different sensitivities were calculated when different deficient plasmas were used, which was not explained by differences in concentrations of the other factors in them or by matrix effect of lyophilized materials compared to freeze thaw specimens, because they also showed differences when thrombin generation tests were performed on deficient plasmas. 6 The authors of this article recommended against following the guideline in routine laboratories and suggested that the manufacturer's data should be used or that the sensitivities should be calculated by processing samples of patient's with single-factor deficiencies, instead. In our study, we followed the CLSI guideline procedure 4 and also calculated the sensitivities by analysing data obtained from the plasma of patient's with a single factor deficiency and demonstrated that our APTT reagent instrument combination (micronized silica) had high sensitivity (>30IU/dL) to all factors evaluated, except prothrombin, by following the CLSI guideline.…”

“…However, more recently, it has been shown that, although this guideline is feasible, 5 different results were obtained when using different deficient plasmas source, lyophilized or frozen, or lyophilized from different manufacturers. 6 The objective of this study was to calculate the sensitivity of the PT and APTT, used in our laboratory, to various factor levels by following the guideline procedure and to compare the results with those obtained using plasmas from patients with a single factor deficiency.…”

Investigation of sensitivity for coagulation factor deficiency in APTT and PT: how to perform it?

“…Lawrie et al suggested that lyophilized deficient plasmas may contain procoagulant material [10]. They concluded that determination of APTT factor sensitivity in accordance with the CLSI guidelines can give inconsistent and misleading results.…”

“…They concluded that determination of APTT factor sensitivity in accordance with the CLSI guidelines can give inconsistent and misleading results. The use of well-defined patient samples was recommended [10].…”

Influence of vitamin K antagonist treatment on activated partial thromboplastin time

“…Very low FIX in patients on VKA treatment, due to mutation in the FIX gene, with prolonged aPTT have been described, but is very rare [2]. This relationship likely depends also on the combination of aPTT reagent and instrument utilized and aPTT reagents differ largely in sensitivity to coagulation factor deficiency [3]. Although aPTT measurement is not indicated in VKA monitoring, the aPTT is widely used as part of a coagulation screening panel.…”