Human α1‐microglobulin: Its measurement and clinical significance

Abstract

α₁‐Microglobulin (α₁‐M), also called protein HC, is a low‐molecular‐weight (LMW) glycoprotein (about 30 kDa) with unique physicochemical properties. Using purified urinary α₁‐M as a standard and specific antibody against α₁‐M, an assay system for α₁‐M was developed, and the clinical significance of this protein was investigated by measuring total levels of α₁‐M under physiological and pathological conditions. α₁‐M is distributed in various body fluids: in serum, it consists mainly of free LMW α₁‐M and monomeric IgA–α₁‐M complex. The total α₁‐M level in serum and urine usually reflects LMW α₁‐M variation sensitively, and its determination is quite useful as an indicator of renal glomerulotubular dysfunction and hepatic dysfunction. Serum levels can vary, depending on IgA‐α₁‐M complex level, in parallel with the IgA concentration. The heterogeneity of α₁‐M purified from different sources of urine by different procedures and underestimation of IgA‐α₁‐M complex by solid‐phase antibody assays can be important causes for the discrepancy of serum levels between assays.