Antiserum to pregnancy-associated plasma protein A (PAPP-A) recognizes human haptoglobin

The presence of pregnancy-associated plasma protein A (PAPP-A) in non-pregnancy serum has been questioned with reference to insufficient specificity of the antibodies raised against this glycoprotein in some departments and used in immunoassay. For convenience, but also because of this unclear situation, many laboratories now use the only commercially available anti-PAPP-A preparations in their assays. By analysing pregnancy and non-pregnancy serum with two-dimensional electrophoresis (2-DE) and Western blotting, we could demonstrate that this antiserum marketed by Dakopatts (Denmark) was capable of binding haptoglobin whereas our own (Dr P. Bischof) antibody preparation did not recognize haptoglobin.