The R and CI Values from Thromboelastography (TEG) May be the Risk Predictors for Low-Dose Emicizumab in Chinese Pediatric Hemophilia Patients

Introduction: Emicizumab (EMI) is widely used in patients with Hemophilia A. Previous studies indicate that in developing countries, many patients use EMI below the standard dose, making monitoring during use necessary. However, EMI's effect on coagulation-related indices complicates monitoring in these patients. Previous research supports the use of a human-derived chromogenic substrate method to assess FVIII-like activity. However, not all laboratories are capable of measuring drug concentration and FVIII-like activity, while testing thromboelastography (TEG) is relatively simple. Our study, by analyzing various TEG parameters and their correlation with FVIII-like activity and EMI concentration, attempts to find a simpler method to monitor the coagulation status in Chinese pediatric patients with hemophilia A.

Methods: We conducted a retrospective study on children with Hemophilia A at Beijing Children's Hospital. Data were collected from March 2023 to July 2024 for patients who underwent EMI treatment. Laboratory tests performed included TEG, FVIII-like activity, and EMI concentration during the loading period (just prior to the first maintenance dose) and throughout the maintenance period. FVIII-like activity was measured using the human-derived chromogenic substrate method, and EMI drug concentration were measured using the modified one-stage assay. We used Spearman's rank correlation analysis to explore relationships among TEG parameters, EMI concentration, and FVIII-like activity.

Results: Forty-four Hemophilia A patients without inhibitor, treated with EMI, were included in the study. Their median age was 4 years (range 0.1-11), with a Body Mass Index of 16.1 (range 12.4-25.7). Of these, seven had moderate and thirty-seven had severe hemophilia. During the loading period, 24 patients received a median weekly EMI dose of 2.7 mg/kg (range 2.1-2.3). Median EMI concentration was 53.6 μg/ml (range 31.8-79.9), with median FVIII-like activity at 17.4 IU/dl (range 15.4-35.4). Spearman's rank correlation analysis revealed a strong positive correlation between FVIII-like activity and EMI concentration (r=0.6491, p=0.0006). In the maintenance period, 40 patients received treatment with a median monthly EMI dose of 5.2 mg/kg (range 1.6-6.4). Their median EMI concentration was 52.6 μg/ml (range 17.8-73.8), and median FVIII-like activity was 16.2 IU/dl (range 4.3-33.3). A continued strong correlation persisted between FVIII-like activity and EMI concentration (r=0.6636, p<0.0001). EMI concentration negatively correlated with the R-value of TEG (r=-0.4112, p=0.0127), and FVIII-like activity showed correlations with both the R-value (r=-0.4497, p=0.0059) and Clotting Index (CI) of TEG (r=0.3338, p=0.0466). Thirty-seven patients (92.5%) had CI within the normal range (-3 to 3), but three patients (7.5%) displayed CI outside the normal range, with values of -5.7, -3.4, and -3.3, and corresponding R values of 9.2, 10.2, and 10.3 minutes. Their respective FVIII-like activity were 10.5 IU/dl, 10.4 IU/dl, and 14.6 IU/dl.

Conclusion: Our study presents the characteristics of EMI concentration and FVIII-like activity in Chinese pediatric hemophilia patients. It finds that prolonged R-values and reduced CI-values may indicate lower FVIII-like activity, suggesting a risk of bleeding. These findings imply that R and CI values of TEG could serve as important predictors of bleeding risk, offering valuable insights for monitoring the coagulation status during EMI treatment.