True hyperammonaemia is clinically
dominated by 4 groups of disorder: urea cycle defects, organic
acidaemias, fat oxidation defects and liver failure / impairment.
In addition, 'transient hyperammonaemia of the newborn' can present
in the first 48 hours with levels usually in excess of
Any child with encephalopathy of unknown cause should have ammonia
Request on ICE
Analysed urgently if specific criteria
Investigation of encephalopathy of
unknown cause in children. Initial symptoms of hyperammonaemia may
include lethargy, refusal of feeds, vomiting, irritability,
seizures and tachypnoea (ammonia is a respiratory stimulant and
presence of respiratory alkalosis is an important sign).
The commonest reason for a raised
ammonia on testing is a poorly taken or processed sample. Samples
should transported to laboratory immediately.
Separate within 30 minutes of sample
collection and analyse immediately. If immediate analysis not
possible, freeze at minus 20'C.
Causes for Rejection
Unlabelled or incorrectly labelled
sample; not meeting specific criteria for analysis; delay in sample
reaching laboratory or in wrong sample container
Males 16 - 60 umol/L
Females 11 - 51 umol/L
Levels are higher in the neonatal
period but a persistent neonatal level greater than
100 µmol/L, in the absence of an obvious cause, requires
Sick preterm neonates, in the absence
of an inherited metabolic disorder, may have moderate elevation of
ammonia (up to 200µmol/L), particularly if there is infection or