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 (Infinity kit = 1.12 x Vitros 250 + 39, R2 = 0.95, n = 105). However, clinically important discrepancies ranging from 100 to 380 micromol/L were found in patients with acute liver failure. Ammonia concentration measured with the enzymatic Infinitytrade mark kit increased by 137 micromol/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.