Spurious elevation of AST in a newborn due to a macroAST of maternal origin

Background Macro-aspartate aminotransferase (macroAST) is a high molecular mass form of AST, formed by immunoglobulin binding to circulating enzyme, that reduces clearance and increases AST activity, leading to diagnostic confusion and unnecessary procedures. MacroAST should be considered a benign finding, widely described in adults and occasionally in children. Case Report A 3450 g Caucasian female neonate (M) was born at 40+5 weeks of gestation by vaginal delivery. Apgar scores at 1 and 5 minutes after birth were 9 and 10. Since the last delivery, 4 years before, the mother had isolated AST elevation, without elevation of ALT. She was investigated by liver and heart ultrasound and blood testing for viral, metabolic and autoimmune hepatic diseases without finding any abnormality. Hemolytic, muscular and myocardial causes of elevated AST activity were excluded. Polyethylene glycol (PEG) precipitation test and AST isoenzyme electrophoresis detected a circulating macroAST. M was discharged from the neonatal department at 72 hours of life. After 2 days was readmitted for weight loss and jaundice due to maternal hypogalactia, solved after rehydration and phototherapy. As in the mother, blood testing showed isolated AST elevation in the absence of clinical and biochemical signs of organ disfunction. Being aware of the maternal macroAST, M was not subjected to any procedure except for a liver ultrasound which was negative. The PEG precipitation study confirmed the presence of a macroAST even in the newborn. A follow-up evaluation at 2 months revealed a progressive decrease of AST activity in the infant’s serum, explained by the disappearance of macroAST of maternal origin (Table 1). The diagnosis of macroAST was added to the clinical file and the mother was reassured. Conclusion M showed an isolated AST elevation as a result of passively acquired maternal macroAST. Prompt diagnosis of macroAST let us to avoid unnecessary procedures in a neonate. To our knowledge, this is the first case of transplacental transfer of macroAST reported. Circulating macroenzymes should be suspected also in neonates whenever an isolated, unexplained increased enzyme activity is found, and the mother should be evaluated as source of that finding. Informed consent to publish has been obtained from the parents.