25-OH Vitamin D3-BSA is a hapten-carrier protein conjugate formed by coupling 25-OH Vitamin D3 to bovine serum albumin (BSA). As a hapten, 25-OH Vitamin D3 alone cannot induce an immune response and must be conjugated to a large molecular protein to become a complete antigen with immunogenicity. 25-OH Vitamin D3-BSA may be supplied as a lyophilized powder or as a solution. The solution is prepared in 0.01 M PBS (pH 7.4) buffer at a typical concentration of 1 mg/mL.