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

Ann Clin Biochem 2008;45:426-428
doi:10.1258/acb.2008.007175
© 2008 Association for Clinical Biochemistry

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Daniel Juan Herrera,
Steven Moore,
Sarah Heap,
Mary Anne Preece and
Paul Griffiths


Department of Clinical Chemistry, Birmingham Children’s Hospital, Steelhouse Lane, Birmingham B4 6NH, UK


Corresponding author: Mr Daniel Herrera. Email: Daniel.Herrera{at}bch.nhs.uk


Background: Plasma ammonia (PA) measurement is of key importance in thediagnosis and monitoring of some inherited metabolic disordersand to monitor subsequent treatment of hyperammonaemia.

Methods: Over a six-month period, patients’ ammonia concentrations weremeasured in parallel, using an enzymatic–UV kit (InfinityAmmonia 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 ClinicalDiagnostic). Alanine amino transferase (ALT) was added to ahuman plasma sample to investigate its effect on the assessmentof ammonia concentration.

Results: Both methods correlated well (InfinityTM kit = 1.12 x 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 InfinityTM 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 InfinityTMkit which may affect interpretation and influence further clinicalaction. However, this positive interference due to ALT doesnot fully explain the discrepant results observed between thetwo methods in patients with acute liver failure.


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