Clinical Indications

True hyperammoniaemia is clinically dominated by 4 groups of disorder: urea cycle defects, organic acidaemias, fat oxidation defects and liver failure / impairment. In addition, 'transient hyperammoniaemia of the newborn' can present in the first 48 hours with levels usuall in excess of 1,500 umol/L.
Any child with encephalopathy of unknown cause should have ammonia measured.

Request Form 

Combined Pathology Blood form (Yellow/Black)

Availability

Analysed urgently if specific criteria met.

Specific Criteria

Investigation of encephalopathy of unknown cause in children. Initial symptoms of hyperammoniaemia 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

Specimen

Plasma

Volume

1.0 ml

Container

Paediatric EDTA (purple top) or Lithium Heparin (Orange top)

Collection

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

Delay in sample reaching laboratory

Reference Ranges

11 to 55 umol/L. Levels are higher in the neonatal period but a persistent neonatal level greater than 100 umol/L, in the absence of an obvious cause, requires investigation.

Interpretation

Sick preterm neonates, in the absence of an inherited metabolic disorder, may have moderate elevation of ammonia (up to 200 umol/L), particularly if there is infection or hypoxia.