Evaluation of von Willebrand factor and ADAMTS-13 antigen and activity levels in sickle cell disease patients in Kuwait

Sickle cell disease (SCD) is a severe form of hemolytic anemia characterized by chronic hemolysis and is associated with increased thrombotic risk. Elevated von Willebrand factor (vWF) levels in SCD have been attributed to increased secretion and impaired processing by its cleaving protease ADAMTS-13. In this study we measured vWF and ADAMTS-13 antigen and activity levels in our SCD patients. Hematological and biochemical parameters for 59 SCD patients (20 children and 39 adults) were analyzed and compared to 59 age-and sex-matched controls. Commercially available ELISA kits were used to measure vWF and ADAMTS-13 antigen and activity levels in patients and controls. Patients had significantly higher levels of vWF (p< 0.006) and ADAMTS-13 activity (p< 0.006) compared to controls. When patients were analyzed according to age and genotype, adult patients (23 SS and 16 S beta degrees thal) maintained higher vWF antigen levels (p< 0.001), but with reduced ADAMTS-13 activity to vWF: Ag ratio (p< 0.003) compared to controls. Pediatric patients (8 SS and 12 S beta degrees thal) had comparable vWF antigen levels to controls (p > 0.05), but had higher levels of ADAMTS-13 activity (p< 0.011) and ADAMTS-13 activity to vWF: Ag ratio (p< 0.038). Age is an important factor to consider when vWF and ADAMTS-13 proteins are analyzed among our patients. Increased vWF in adult patients may be attributed to increased production and resistance of vWF to proteolysis rather than ADAMTS-13 deficiency. This outcome was not seen in pediatric patients as higher ADAMTS-13 activity maintained vWF antigen at comparable levels to normal controls.