[Analysis of APTT Mixing Test Results in Factor Ⅷ Inhibitor-Positive Hemophilia Patients]

OBJECTIVE

To analyze the results of activated partial thromboplastin time (APTT) mixing test in coagulation factor Ⅷ inhibitor-positive hemophilia patients, so as to increase the value of APTT mixing test in the screen of factor Ⅷ inhibitor.

METHODS

Eighty plasmas samples with different titers of coagulation factor Ⅷ inhibitors had been collected and diluted for routine immediate APTT mixing test and at 37 ℃ 2 hours incubation APTT mixing test. Fifteen samples were selected for immediate and normal temperature incubation for 15 min, 30min, 1 hour, 2 hours and 37 ℃ for 30 min, 1 hour, 2 hours APTT mixing test.

RESULTS

The results of APTT mixing test were significantly correlated with the titers of coagulation factor Ⅷ inhibitors. The ROC curve result showed that the best diagnostic cut-off value for 2 hours incubation APTT mixing test at 37 ℃ to determine the presence or absence of coagulation factor Ⅷ inhibitors was 43.8 s (sensitivity and specificity was 85.90% and 100%, respectively), while the best diagnostic cut-off value for distinguishing high-titer and low-titer Ⅷ inhibitors was 52.4 s (sensitivity and specificity was 98.18% and 95.65%, respectively). The critical coagulation factor Ⅷ inhibitor titer that could not be corrected by immediate APTT was 5.14 BU/ml, while that could not be corrected by 37 ℃ 2 hours incubation APTT was 1.31 BU/ml. Paired samples t -test was performed on the APTT mixing test results at different times and temperatures, and the differences were statistically significant (P < 0.05).

CONCLUSIONS

The APTT mixing test can be used as a screening index for coagulation factor Ⅷ inhibitors. APTT mixing test result shows a significant time-temperature dependence with lower titers of coagulation factor Ⅷ inhibitor. Patients with hemophilia who cannot be corrected by immediate APTT mixing test should be alert to the possibility of high titer of coagulation factor Ⅷ.