Characteristics of Sickle Cell Disease Children Having Elevated Thrombin Potential

Abnormalities of the clotting system are often observed in sickle cell disease (SCD). In addition to activation of coagulation, increased thrombin generation (TG) has recently been demonstrated in SCD children

To characterize the group of SCD children with increased TG in terms of clinical and biological parameters.

TG was performed in the platelet-poor plasma of 97 SCD children at steady-state and 80 controls aged between 2 and 20 years. TG was triggered using 1 pM tissue factor and 4μM synthetic phospholipids with thrombomodulin to activate the protein C/protein S anticoagulant pathway. The Endogenous Thrombin Potential (ETP) and the peak height were analyzed. As these parameters increase with age in normal children, controls were distributed in 4 categories of age: [2–5], [6–10], [11–15] and [16–20] years. The mean ETP and the mean peak were calculated for each age category. A ratio for ETP (r ETP) and a ratio for the peak (r Peak) were defined for each control and patient as follows: individual ETP/ mean ETP and individual peak/ mean peak according to age category. Overall mean of r ETP and r Peak was then calculated such as to eliminate bias due to age. This calculated mean was 1.00 (0.39 – 1.61) for r ETP and 0.99 (0.28 – 1.81) for r Peak in controls. TG was considered abnormal if r ETP or r Peak value was above the mean + 2SD of controls (r ETP≥ 1.62 and r Peak≥ 1.82). Clinical and laboratory parameters were compared between SCD children having normal or increased ratios using the Mann Whitney test for numbers or the Fisher's exact test for proportions. P < 0.05 was considered significant.

Overall 48 (49.4 %) patients showed either high r ETP or high r Peak whereas both parameters were increased in 31 (31.9 %) patients. As shown in Tables I and II, SCD children with elevated ratios were characterized by a younger age, shorter duration of hydroxyurea (HU) treatment, lower total hemoglobin level, higher reticulocyte and monocyte counts, higher LDH and D-dimer levels and a trend to increased procoagulant microparticle level (PMP) as compared with those having normal ratios. The higher D-dimer level in the group with abnormal ratios indicates that these children also manifest a higher degree of coagulation activation than those with normal ratios. Differences observed with markers of hemolysis are consistent with other reports suggesting a link between hypercoagulability and high hemolytic rate in SCD. The borderline significance of PMP is probably due to the use of exogenous phospholipids in TG which reduces the sensitivity of the test to endogenous phospholipids at the surface of PMPs.

According to our study, Elevated Thrombin Potential is more frequently encountered in SCD children of younger age, with a shorter duration of HU treatment and with increased rate of hemolysis. These observations together with elevated D-dimer level seem to characterize SCD children with a hypercoagulable state.

No relevant conflicts of interest to declare.