Methods of preparing a solid reference material so as to elicit a positive control response when tested for in-vitro complement activation include providing biological tissue； treating the tissue with an aqueous cellulose solution for a time sufficient to allow fluid in the tissue to be replaced by the aqueous cellulose solution； drying the cellulose-treated tissue by a vacuum-drying process or a lyophilization process to form dried tissue； and storing the dried tissue in a dry, ambient environment. The tissue prepared by these methods and its use in an in-vitro complement assay and diagnostic kit are also described.
