CH50 and Its Use in the Allergist–Clinical Immunologist's Practice

Abstract

The CH50 reflects the ability of serum complement to lyse sheep red blood cells (RBCs); its value is the reciprocal of the dilution of serum to lyse 50% of antibody coated sheep RBCs. Reduction of the CH50 occurs when individual complement component(s) are deficient or consumed. The CH50 may be useful for a variety of medical specialties and is most helpful diagnostically when laboratory results are interpreted in the context of the history and physical exam. The primary utility of the CH50 in the practice of an allergist-immunologist is to screen for complement-deficiency associated immunodeficiency (primarily classic or terminal complement component deficiencies) and some vasculitides (usually immune-complex induced and/or small vessel vasculitis). Absent or significantly reduced individual complement components may result in recurrent sinopulmonary bacterial infections, Neisserial meningitis, or sepsis. A reduced CH50 in this situation warrants quantification and functional assays of individual complement components The sensitivity and specificity of a reduced CH50 limit the value of using this test for vasculitis screening unless painful, persistent urticarial lesions or purpura is observed. Thus, the CH50 has definite limitations but serves as a costeffective, screening test with the appropriate clinical presentation.