Hemopexin: a review of biological aspects and the role in laboratory medicine

Background: Hemopexin is a heme-binding plasma glycoprotein which, after ha ptoglobin, forms the second line of defense against hemoglobin-mediated oxi dative damage during intravascular hemolysis. A decrease in plasma hemopexi n concentration reflects a recent release of heine compounds in the extrace llular compartment. Heme-hemopexin complexes are delivered to hepatocytes b y receptor-mediated endocytosis after which hemopexin is recycled to the ci rculation. Methods of analysis: Immunonephelometric and -turbidimetric hemo pexin assays are available as more precise and rapid alternatives to the ra dial immunodiffusion technique. Interpretations: Hemopexin determinations a re not subject to interference by in vitro hemolysis. Altered serum or plas ma concentrations of hemopexin are found not only in hemolytic anemias but also in other conditions Such as chronic neuromuscular diseases and acute i ntermittent porphyria. In laboratory medicine, while hemopexin determinatio n in tandem with haptoglobin has potential applications in the assessment o f intravascular hemolysis and allows for the monitoring of the severity of hemolysis after depletion of haptoglobin, its diagnostic utility is less cl ear in other pathological conditions. Further studies are necessary to full y establish the clinical significance of hemopexin determination. (C) 2001 Elsevier Science B.V. All rights reserved.