Ammonia

Keywords: NH3

Specimen:

5 mL blood in lithium heparin tube or 1 mL in paediatric tube, placed on ice. Plasma must be separated and assayed or frozen immediately.

Ammonium heparin tubes must not be used for collection.

Method:

Spectrophotometry.

Reference Interval:

<50 µmol/L (age related).

Application:

Significant hyperammonaemia during childhood can be observed with urea cycle defects, many of the organic acidaemias, transient hyperammonaemia of the newborn (THAN), and fatty acid oxidation defects.

Investigation of unexplained encephalopathy, especially if associated with vomiting.

Interpretation:

Increased levels occur in genetic hyperammonaemias and are frequently seen in hepatic coma, especially with gastrointestinal bleeding. However, it is not a reliable or useful test for this condition.

Reference:

Burton BK. Clin Liver Dis 2000; 4: 815-830.