Myoglobin is a respiratory protein that is unique to skeletal and cardiac muscle. It is composed of a single polypeptide chain of 153 amino acids, with an iron-containing, heme-prosthetic group, and has a molecular weight of approximately 17,800. Its function is thought to involve the transport of oxygen across the cell, and the modulation of oxygen's availability for cellular reactions of respiration. In the course of muscle disorders or stress, myoglobin may leak from muscle tissue to the circulation, and from there may appear in the urine.1
Within the past several years, application of sensitive immunologic methods has allowed the detection and quantification of myoglobin in the circulation. Although many types of disorders have been studied, this discussion will highlight three areas, as follows: myocardial disease, genetic disorders of muscle, and acquired skeletal muscle disease.
Increased levels of serum myoglobin occur in most, if not all, patients during the