Can plasma ammonia be measured in patients with acute liver disease?

Abstract

Background Plasma ammonia (PA) measurement is of key importance in the diagnosis and monitoring of some inherited metabolic disorders and to monitor subsequent treatment of hyperammonaemia. Methods Over a six-month period, patients' ammonia concentrations were measured in parallel, using an enzymatic–UV kit (Infinity Ammonia Liquid Stable Reagent, Thermo Electron Corporation, Australia) on an Olympus AU640 analyser (Olympus UK Ltd, Hertfordshire) and on our current dry chemistry system (Vitros 250, Ortho Clinical Diagnostic). Alanine amino transferase (ALT) was added to a human plasma sample to investigate its effect on the assessment of ammonia concentration. Results Both methods correlated well (InfinityTM kit = 1.12 × Vitros 250 + 39, R2 = 0.95, n = 105). However, clinically important discrepancies ranging from 100 to 380 μmol/L were found in patients with acute liver failure. Ammonia concentration measured with the enzymatic Infinity™ kit increased by 137 μmol/L when ALT was added up to 17,000 IU/L. Conclusions ALT produces a positive interference in the enzymatic Infinity™ kit which may affect interpretation and influence further clinical action. However, this positive interference due to ALT does not fully explain the discrepant results observed between the two methods in patients with acute liver failure.