Abnormally high level of C4b binding protein and deficiency of free fraction of protein S in a patient with systemic lupus erythematosus and recurrent thromboses.

A patient with systemic lupus erythematosus and numerous thrombotic accidents was found to have a deficiency of the free fraction of protein S, most likely due to an abnormally high level of C4b binding protein. These abnormalities, unique in comparison to 4 other patients with hypercoagulation states, were partially corrected with cyclophosphamide. There was no evidence of a consumption of complement components. The interactions between the hemostasis system and the complement cascade are discussed.