On the degradation of amino acids, the amine group is released as highly toxic ammonia. Normally this is swiftly removed by the liver where it is converted into urea by means of the urea cycle. Hyperammonia may arise in pre-term babies, liver failure or inborn errors of metabolism affecting the urea cycle enzymes or metabolism of organic acids.
The increased amount of ammonia in these conditions affects normal metabolic function in the brain that may lead to neurological changes and eventually death.
Ammonia also causes a metabolic acidosis which is difficult to correct.
Adult: 11.2 – 34.5 umol/L
Paediatrics: 34 – 102 umol/L
Plasma (EDTA or heparin).
The ammonia in the separated plasma should be stable for about 3 hours at 4 – 8°C. The sample should arrive on ice (if possible) and plasma be separated immediately. The sample should be brought to the laboratory immediately after venepuncture and handed to a member of staff as an urgent request. If analysis is delayed the separated plasma must be kept in fridge.