Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
Clinical background:
Measurement of ammonia should be a first line biochemical investigationin the acutely ill neonate/infant and also in cases of unexplained altered mental state or prolonged vomiting without diarrhoea in patients of any age.Hyperammonaemia results from defective catabolism of amino acids to urea. Ammonia is neurotoxic and symptoms of hyperammonaemia are essentially neurological but with varying severity and age of onset.
The following guidelines are available:
- British Inherited Metabolic Diseases Group (BIMDG) Emergency guideline for management of undiagnosed hyperammonaemia
- UK Metabolic Biochemistry Network (MetBioNet) guideline on investigation of hyperammonaemia
Specimen container paediatric:
EDTA plasma
Specimen container adult:
EDTA plasma
Minimum volume paediatric:
0.5 mL blood
Minimum volume adult:
0.5 mL
Special requirements:
The laboratory will analyse all samples received. However to minimise falsely high results samples should be placed on ice following collection and brought immediately to the laboratory. Please contact the laboratory to inform that sample is being sent.
Sample stability:
Falsely high results may be obtained if samples are kept unseparated at ambient temperature.
Transport requirements:
Bring immediately to laboratory, marked for urgent analysis. Transport on ice is strongly recommended, although if ice not available laboratory will still perform analysis.
Interpretation:
Ammonia > 200 µmol/L in neonates or > 150 µmol/L in older patients requires immediate attention. Consider contacting a Metabolic specialist.
Causes of hyperammonaemia can be split into:
Inherited metabolic disorders: including urea cycle defects, other amino acid disorders, organic acidurias, fatty acid oxidation defects
Acquired causes: including liver dysfunction and certain medications
Artefactual/other: including sample haemolysis, delayed analysis, transient hyperammonaemia of newborn.
First line investigations into hyperammonaemia requires:
Repeat plasma ammonia
Blood gases
U&E
LFT
Clotting screen
Plasma glucose
Plasma lactate
Serum/plasma calcium
Blood cultures
Urine ketones
If an inherited metabolic cause is suspected then the following tests should be requested, before initiation of treatment if at all possible:
Urine organic acids
Urine and plasma amino acids
Urine orotic acid
Blood spot acylcarnitines
Reference ranges:
0 – 4 week: 0 – 100 µmol/L
4 weeks and older: 0 – 50 µmol/L