IL33 and sickle cell disease: Plasma IL-33 levels were comparable in 44 patients with sickle cell disease with osteonecrosis of the femoral head as compared with 24 patients with sickle cell disease without ONFH (2.05 ± 4.57 pg/mL versus 1.50 ± 2.89 pg/mL, p-value = 0.590).