Serum enzymes: a guide to the aetiology of burn injury

Abstract

PATIENTS are often admitted to the burns treatment centre with little recollection of the circumstances of their injury. This is particularly true of elderly patients who may suffer burn injury following a syncopal attack. For patient management it may be helpful to investigate the circumstances of the injury to ascertain if cardiac ischaemia or electrical burn injury has occurred. In this situation measurement of the levels of selected serum enzymes may be helpful. In this paper we have investigated the levels of the enzymes creatine kinase (CK), aspartate aminotransferase (ASAT) and hydroxybutyric dehydrogenase (HBD) in the serum of 6 patients who suffered either flame or electrical burn injury. From this it was possible to determine how much muscle damage occurred as a result of the injury or whether a myocardial infarct was a causative factor in the accident. Enzymes found in the serum are usually present as a result of leakage from damaged or diseased tissues. They may also arise from erythrocytes should significant intravascular haemolysis occur. CK occurs both in skeletal and heart muscle, while HBD occurs predominantly in heart muscle. ASAT is found in many tissues including erythrocytes, muscle, heart and liver but elevation in serum activity is highest following liver damage. Thus, the finding of elevated ASAT levels in serum with relatively normal CK levels is an indication of acute or chronic liver damage. Heart and skeletal muscle damage may be differentiated by measuring the levels of CK and HBD in the serum. Damage to skeletal muscle is seen as raised levels of CK with little or no elevation of HBD, whereas damage to cardiac muscle results in elevation of both enzymes. These enzymes can only be used as indicators of acute muscle damage since the slow breakdown of muscles associated with wasting does not result in marked elevation of serum CK levels. The results presented, consisting of 6 Case Reports on pairs of patients sustaining burns of comparable severity but different aetiology, suggest that a laboratory request for a ‘cardiac enzyme investigation’ on days 2-4 after injury (the day of injury being day 0) may well be of value in indicating hitherto unsuspected cardiac involvement and muscle damage caused by equivocal electrical injuries such as radiant electric fire burns.