DISCRIMINATION BETWEEN MYOCARDIAL AND SKELETAL-MUSCLE INJURY BY ASSESSMENT OF THE PLASMA RATIO OF MYOGLOBIN OVER FATTY-ACID-BINDING PROTEIN

Background Myoglobin and fatty acid-binding protein (FABP) each are us eful as early biochemical markers of muscle injury. We studied whether the ratio of myoglobin over FABP in plasma can be used to distinguish myocardial from skeletal muscle injury. Methods and Results Myoglobin and FABP were assayed immunochemically in tissue samples of human hea rt and skeletal muscle and in serial plasma samples from 22 patients w ith acute myocardial infarction (AMI), from 9 patients undergoing aort ic surgery (causing injury of skeletal muscles), and from 10 patients undergoing cardiac surgery. In human heart tissue, the myoglobin/FABP ratio was 4.5 and in skeletal muscles varied from 21 to 73. After AMI, the plasma concentrations of both proteins were elevated between appr oximate to 1 and 15 to 20 hours after the onset of symptoms. In this p eriod, the myoglobin/FABP ratio was constant both in subgroups of pati ents receiving and those not receiving thrombolytics and amounted to 5 .3+/-1.2 (SD). In serum from aortic surgery patients, both proteins we re elevated between 6 and 24 hours after surgery, the myoglobin/FABP r atio was 45+/-22 (SD), which is significantly different from plasma va lues in AMI patients (P<.001). In patients with cardiac surgery, the r atio increased from 11.3+/-4.7 to 32.1+/-13.6 (SD) during 24 hours aft er surgery, indicating more rapid release of protein from injured myoc ardium than from skeletal muscles. Conclusions The ratio of the concen trations of myoglobin over FABP in plasma from patients with muscle in jury reflects the ratio found in the affected tissue. Since this ratio is different between heart (4.5) and skeletal muscle (20 to 70), its assessment in plasma allows the discrimination between myocardial and skeletal muscle injury in humans.