engleski

Visual inspection of the aPTT reaction curve as a reliable screening tool for detecting the presence of FVIII and FIX inhibitors

Background: Specific shapes and slopes of the aPTT reaction curve are characteristic for patients with congenital or acquired FVIII/FIX deficiency. Questionable aPTT results are flagged by the analyzer and should be visually inspected. Aims: To investigate the possibility to detect the presence of FVIII/FIX inhibitors by analyzing flagged aPTT results after visual inspection of reaction curves and manual measurement of the reaction curve angle (RCA). Materials and Methods: The study included 131 patient plasma samples with request for the determination of FVIII/FIX inhibitors. aPTT was performed using Actin FS on Atellica COAG 360 (Siemens, Germany) at 405 nm with manufacturer’s proposed evaluation method DRIFTING BASELINE (DB) and checking method ANGLE DB that flagged aPTT results with RCA<30 degrees. All aPTT reaction curves were visually inspected and RCA were manually measured. FVIII and FIX activities were determined by one-stage clotting assay. Inhibitor titers were determined using Nijmegen modified Bethesda assay. Patients were divided according to the absence (group I, n=103) or presence (group II, n=28) of inhibitors. Results: Excellent correlation between FVIII activities (median:11.0 U/dL, range:0.9–139 U/dL) and RCA (median:53 degrees ; range:13.0–78.0 degrees) was obtained for all tested samples (r=0.932 ; P<0.001). Statistically significant difference of RCA (P<0.001) was identified between group I (median:58 degrees ; range:13.0–78.0 degrees) and group II (mean:31.6 degrees ; range:19.0– 56.0 degrees). ROC analysis revealed that RCA of 51 degrees allowed distinguishing between two groups of patients with sensitivity of 96.4% and specificity of 67.0% , while predefined RCA of 30 degrees showed the sensitivity of 57.1% and specificity of 81.6%. Conclusions: Based on obtained results, it may be concluded that ANGLE DB checking method, together with visual inspection of aPTT reaction curve and angle measurement, provides a simple and reliable tool to screen for the presence of FVIII/FIX inhibitors.

aPTT reaction curve ; reaction curve angle (RCA)

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