Impact of Hydroxyurea on Thrombin Antithrombin Complex and Vaso-Occlusive Crisis in Pediatric Sickle Cell Disease.

Background: Several studies suggest that increased activity of the coagulation system may be important in the pathogenesis of vascular occlusion in sickle cell disease. Hydroxyurea (HU) has been shown to reduce the frequency of vaso-occlusive manifestations in both adults and children with sickle cell disease (SCD).

Aim: To analyze the effect of HU on Thrombin-Antithrombin (TAT) as a marker of thrombin generation and hypercoagualbility in SCD and to find out the relation between TAT level and vaso-occusive crisis.

Subjects and Method: we evaluated 37 child with sickle cell hemoglobinopathy (mean age 10.92±5.39 years) and 15 normal control children (mean age 9.75±6.34 years). Informed consent was obtained from patients and/or guardians and study approval by local IRB was obtained. Twenty-two patients (59.5%) were on HU, 15 (41.5%) patients did not receive HU, 7 (46.7%) of them were transfusion dependant. TAT assay was done in vitro using a sandwich enzyme immunoassay.

Results: Mean patients’ age at institution of HU was 8.54± 3.85 years with median treatment duration of 4.5 years. Causes for initiating HU therapy were frequent blood transfusion in 11 patients (50%), frequent pain crisis (≥ 3/year) in 9 patients (41%), severe anemia and parents refusing blood transfusion in 1 patient (4.5%) and stroke in another patient (4.5%). HU dose was 20.82±4.95 mg/kg/day. We measured TAT in all patients and compared them to healthy control. There was significant difference in TAT level in sickle cell patients (198.86±185.7) compared to healthy control 2.91±0.94, [P value < 0.0001]. When the level of TAT was compared between the HU and non-HU groups we found that patients on HU had statistically significant lower TAT level (172.36 vs.225.37) [P=0.039]. There was also a significant negative correlation between HU dose and TAT level (p=0.03). A significant positive correlation between number of vaso-occlusive crisis/year [P=0.03], frequency of pain crisis/year [P=0.04], duration of pain crisis [P=0.03] and TAT level was observed.

Conclusion: Hydroxyurea has significant inhibitory effect on thrombogenesis in sickle cell patients, which may be another mechanism for reducing vaso-occlusive crisis. Sickle cell children with higher TAT level had more frequent and severe vaso-occlusive crisis.