Interstitial Fluid Concentrations of Albumin and Immunoglobulin G in Normal Men

By a wick method human interstitial fluid was collected from the subcutaneous tissue of the forearm. Nine normal men had an average interstitial fluid albumin concentration (Ci) of 2.92 g/100 ml (S.D. 0.32) and a ratio between interstitial albumin concentration and serum albumin concentration (Ci/Cs) of 0.62 (S.D. 0.09). The corresponding values for IgG were 0.65 g/100 ml (S.D. 0.18) and 0.52 (S.D. 0.12) respectively. Evidence is presented showing that subcutaneous interstitial fluid may be representative of interstitial fluid in the whole body with regard to the concentrations of the two proteins. The microvascular permeability in subcutis is greater for albumin than for IgG, the subcutis being perhaps a little more permeable to IgG relative to albumin than the average total body. The available data do not allow one to differentiate between the relative role of the three macromolecular trans-vascular transport mechanisms, diffusion, filtration, and pinocytosis, but it is likely that the transport is not by pure diffusion.