APTT critical value establishment in four different reagent/instrument systems based on single factor deficiencies

There are significant differences in the activated partial thromboplastin time (APTT) critical values reported in different studies, most of which does not make recommendations for any specific clear detection systems. The International Council for Standardization in Hematology (ICSH) recommends that APTT critical values be established based on the reagent type, coagulation factor sensitivity and heparin response. The objective of this study was to establish APTT critical values by using different reagents and based on single coagulation factor deficiencies.

The APTT values were determined in commercial endogenous coagulation factor-deficient plasma at concentrations of 1 IU/dL, 2 IU/dL, 5 IU/dL, 10 IU/dL, 20 IU/dL, and 30 IU/dL by using four assay systems. The retrospective collection of data from patients who lacked factor VIII (FVIII), FIX, or FXI alone was performed. Receiver operating characteristic (ROC) curves were constructed to assess the diagnostic accuracy of APTT for identifying patients with an endogenous coagulation factor activity < 5 IU/dL.

The APTT values in the plasma samples with the same concentrations of endogenous coagulation factors were significantly different among the four assay systems (P < 0.001). The suggested critical values of APTT were 40.0 s for Sysmex CS5100 (Actin FSL), 58.0 s for Sysmex CS5100 (Actin), 51.8 s for STA-R Evolution (STA-PTTA), and 64.8 s for ACL TOP 700 (HemosIL SynthasIL). On the basis of the ROC curve, the optimal threshold values for APTT (STA-PTTA) were 55.8 s in patients with a simple deficiency of FVIII (sensitivity = 100%, specificity = 85.7%, area under the ROC curve (AUC) = 0.982), 54.3 s in patients with a simple deficiency of FIX (sensitivity = 100%, specificity = 92.9%, AUC = 0.986), and 71.7 s in patients with a simple deficiency of FXI (sensitivity = 100%, specificity = 94.1%, AUC = 0.992), which were closer (difference of 0.6-2.5 s) to the cutoff points for commercial plasma at equal factor levels.

APTT critical values need to be established for different reagents based on the presence of a single coagulation factor deficiency.