Method Description

Heat inactivated patient plasma, undiluted and serially diluted, is mixed with an equal volume of normal pooled plasma (NPP). The NPP supplies the factor against which the inhibitor is directed in a known concentration. The patient plasma mixtures, along with a control (Bethesda Pool) of diluted NPP are incubated at 37° C for 2 hours, after which factor activity is measured. The factor activity in the undiluted patient and its serial dilutions are compared to the factor activity recovered in the Bethesda Pool. These values are then used to calculate Bethesda units. One Bethesda unit is defined as the amount of antibody that will destroy 50% of the coagulation factor activity in 2 hours.( Owen CA Jr, Bowie EJW, Thompson JH Jr: Diagnosis of Bleeding Disorders. 2nd ed. Little, Brown and Company; 1975; Meijer P, Verbruggen HW, Spannagi M: Clotting factors and inhibitors: Assays and interpretation. In: Kottke-Marchant K, ed. Laboratory Hematology Practice. Wiley Blackwell Publishing; 2012:435-446)