Specimen Collection

Please phone Labplus to give advance warning a sample is being sent.

Transport of sample:

• Within Auckland City Hospital: Transport specimen on ice without delay .
• If sending from outside Auckland City Hospital: separate immediately and send on ice without delay.

Mark the form as "URGENT".

• The ammonia level rises in stored plasma due to ammonia generation from precursors.
• Samples from outside Auckland City Hospital: If separated samples transported on ice are analysed within 2 hours the increase in ammonia will be insignificant.
• Auckland Hospital samples: if whole blood samples on ice are separated within 1 hour and analysed within 2 hours of collection, the increase will be insignificant.
• A minimum 2 mL specimen is preferred. The test can be performed on a micro-sample, but sweat contamination will increase the ammonia concentration significantly, which makes result interpretation difficult. The skin must be thoroughly cleaned prior to collection of the specimen.

NOTE : A separate EDTA sample NOT ON ICE is required if a FBC is also requested.

Sample stability:

• 30 mins at 15-25 ^o C
• 2 hours at 2-8 ^o C
• 3 days at -20 ^o C

0.5 mL Paediatric EDTA Blood (Always Required)

4 mL EDTA Blood
Reference Intervals

Units: umol/L

Age
Premature neonate	<150
Term neonate	<100
infant / child	<40
Adults	<70

Uncertainty of Measurement: 8% for results around 50 umol/L

8% for results around 100 umol/L

Turnaround Time: Within 3 hours
Diagnostic Use and Interpretation

Causes of increased plasma ammonia:

• hepatic failure
• disorders of the urea cycle
• transient hyperammonemia of the newborn
• valproate therapy

Falsely elevated ammonia results are common:

Concentrations of ammonia in the specimen rise rapidly after collection - specimen must be placed on ice and rapidly sent to the laboratory. In unseparated samples the average rate of increase per hour is 6 umol/L at room temp and 4 umol/L on ice, but may be faster in some patients . After separation the rise is slower but is still significant.

Sweat contains high levels of ammonia - collect blood by venipuncture, not heel or finger-prick

False high values are obtained after muscular exercise or with haemolysis.

Note : the drugs sulfasalazine and sulfapyridine cause interference in the assay; patients on these drugs may have invalid ammonia results.

References

1. UK National Metabolic Biochemistry network: Guidelines for the investigation of hyperammonemia

2. Soldin et al Pediatric Reference Intervals 6th Ed. AACC Press, 2007

3. Walker, V. (2012). Severe hyperammonaemia in adults not explained by liver disease. Ann Clin Biochem 49(Pt 3): 214-228.

Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.

Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427

Last updated at 15:26:00 06/01/2025