Comparison of different methods for ammonia measurement in southern and northern Australia.

Corey Markus, Michael Metz, Robert MacFarlane, Ron Hallawell

Research output: Contribution to journalMeeting Abstractpeer-review


The Royal Darwin Hospital (RDH) serves “Top End” Australia, Alice Springs Hospital (ASH) “Centralia”, and Women's and Children's Hospital (WCH) South Australia. 3000 km separate RDH from WCH, with ASH midway between. Care of children with metabolic disorders at ASH and RDH is shared with the metabolic service of WCH. WCH metabolists wanted to know how plasma ammonia results from ASH and RDH compared to WCH results. A comparison study was conducted to establish the relationship of plasma ammonia results from all 3 hospitals.

Remaining clinical samples of blood collected into EDTA anticoagulant were centrifuged and plasma aliquoted into 3 tubes and frozen at − 70 °C. Samples were transported to RDH and ASH laboratories on dry ice. 50 samples were used for comparison among the three laboratories. Ammonia results ranged from 30 umol/L to 330 umol/L.

At WCH ammonia measurement is performed on a Roche Cobas C501. 2-Oxoglutarate in the presence of ammonium and NADPH is reductively aminated to form l-glutamate and NADP +, by the action of glutamate dehydrogenase. Production of NADP + is directly proportional to ammonia concentration. Decrease in absorbance is used to determine NADP + concentration.

At ASH and RDH ammonia measurement is performed using an Ortho Clinical Diagnostics Vitros 5,1 FS. A sample is placed on a dry slide, the buffer layer then converts ammonium to gaseous ammonia. Gaseous ammonia, after passing through a specific semi-permeable membrane, reacts with bromphenol blue to cause the formation of a blue dye.

Ammonia results from the Northern Territory sites are comparable with results from WCH. The relationship between WCH and RDH results was RDH = 1.03WCH-10 with r = 0.99. The relationship between WCH and ASH results was ASH = 1.09WCH-17 with r = 0.99. The relationship between ASH and RDH results was ASH = 1.03RDH-5 with r = 1.00.

With no reference method or material available for ammonia measurement in human plasma and special pre-analytical requirements, ammonia is a difficult analyte to measure and to compare results from different sites. This study has shown that samples for ammonia measurement, transported appropriately, can be shipped over great distances, and comparable results between laboratories using different platforms are achievable.
Original languageEnglish
Pages (from-to)776
Number of pages1
JournalClinical Biochemistry
Issue number9
Publication statusPublished - Jun 2014
Externally publishedYes


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