HEMOLYTIC AND ANTIGENIC MEASUREMENTS OF COMPLEMENT - A COMPARISON OF SERUM AND PLASMA SAMPLES IN NORMAL INDIVIDUALS AND PATIENTS

  • 1 January 1982
    • journal article
    • research article
    • Vol. 100  (3) , 437-444
Abstract
Over a 2-yr period, 10 patients [6 with polyclonal cryoglobulinemia, 2 with monoclonal cryoglobulinemia and 2 with systemic lupus erythematosus but without cryoglobulins] with a discrepancy between functional and antigenic assays in the routinely employed clinical assays for measuring serum complement concentrations were evaluated. These differences were secondary to cold-dependent activation of the classsical complement pathway in vitro, in some cases by cryoglobulins and in others by unknown means. Plasma samples were procured with commonly used anticoagulants (EDTA, citrate or heparin) that prevent in vitro complement activation. To assess whether plasma samples were suitable for complement determination, a comparison of serum vs. plasma samples for THC total, C4 [complement component 4], C2, C3, factor B and C6 levels in normals and patient populations was undertaken. Only modest differences were found between serum and plasma samples for these functional and antigenic assays except for heparinized samples in which determinations by rate nephelometry produced falsely elevated C4, C3, and factor B antigenic levels. Plasma samples, especially EDTA or citrate, are suitable for complement determinations and could be used either routinely or, more selectively, in patients in whom there is a discrepancy between functional and antigenic determinations.