The reference intervals for normal, age dependent, and ammonia according to the Association of Clinical Biochemistry are1:
Premature neonates: < 150 µmol/L
Term neonates: < 100 µmol/L
Infants: < 40 µmol/L
Adults: 11-32 µmol/L
Measure ammonia in free flowing venous or arterial blood. Avoid use of tourniquets.
WHY? Muscle exertion may increase venous ammonia levels. Be aware if the child is struggling or had physical exercise before blood is drawn.
Collect the required plasma specimen in a pre-chilled sodium heparinized vacuum tube. The specimen should be mixed gently by inversion.
WHY? Heparin is the preferred anticoagulant because it has been shown to reduce red blood cell ammonia production. However, EDTA is another coagulant that can be used.
Immediately place the tube on ice. The sample should be centrifuged within 15 minutes of draw. Alert the laboratory of the STAT nature of the lab order.
WHY? It is crucial to keep blood samples cold after collection, because the ammonia concentration of standing blood and plasma increases spontaneously. Most of this increase has been attributed to the generation and release of ammonia from red blood cells and the deamination of amino acids, particularly glutamine.
The laboratory should process and deliver results in 1 hour.