Pathology Handbook


Clinical Indications

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 1,500 µmol/L.
Any child with encephalopathy of unknown cause should have ammonia measured.

Request Form 

Request on ICE


Analysed urgently if specific criteria met.

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).

Turnaround Time

Same day




1.0 ml


Vacutainer purple top


The commonest reason for a raised ammonia on testing is a poorly taken or processed sample. Samples should transported to laboratory immediately.

Lab Handling

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

Reference Ranges

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 investigation.


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 hypoxia.