Serum secretory component: a potential marker of biliary obstruction.

Secretory Component (SC) was measured in serum samples from patients with a variety of disorders using enzyme-linked immunosorbent assay (ELISA). The overall precision of the method at high and low concentrations of SC was 11% (CV). Serum concentrations of SC were significantly higher in patients with several forms of liver disease (means = 82.37 mg/l +/- SD 56.9) compared with normals (means = 6.0 +/- SD 4.2), patients with diseases of mucosal surfaces (means = 7.4 mg/l +/- SD 4.2) and patients with elevated alkaline phosphatase due to causes other than overt liver disease (means = 16.4 mg/l +/- SD 7.6). Serum SC levels correlated strongly with serum alkaline phosphatase activity (rs = 0.648) in the presence of liver disease. Raised serum SC in liver disease probably reflects reflumeans of biliary SC and secretory IgA into blood due to cholestasis. Estimation of serum SC could be clinically useful as an index of biliary obstruction, especially to distinguish a raised serum alkaline phosphatase activity of liver or bone origin.