Orosomucoid contents of pleural and peritoneal effusions of various etiologies

Orosomucoid (α₁ acid glycoprotein) is a small protein (mw = 45,000) which is formed in the liver. It is considered to be one of the principal serum components of the acute phase reactant proteins. Recently, it has been claimed that orosomucoid concentrations in pleural and peritoneal fluids distinguished neoplastic from nonneoplastic noninflammatory effusions more effectively than the concentrations of total protein, albumin, α₁, α₂, β, or γ globulin. This was checked. Orosomucoid and the contents of 7 other proteins were determined by radial immunodiffusion in sera and in pleural or peritoneal fluids of 66 patients. No significant difference between concentrations of individual proteins in effusions of neoplastic origin and those of nonneoplastic inflammatory origin was found. In noninflammatory fluids, the protein concentrations were lower, but their distribution was similar to distributions in the other fluids tested. These findings support the view that the protein content of effusions reflects changes in vascular permeability.