Comparison of plasma ammonia results from seven different automated platforms in use throughout Central Australia

Introduction The clinical catchment area for the Metabolic service at the Women's and Children's Hospital in Adelaide, South Australia, covers nearly 2.5 million km². Care of children with metabolic disorders in these remote areas is assisted from Adelaide, and at times, using plasma ammonia results from laboratories up to 3000 km away. There are seven different platforms measuring plasma ammonia within this vast clinical catchment area. Hence, a correlation study was conducted to examine the relationship between plasma ammonia results from the seven different platforms in use throughout central Australia. Design & method Multiple aliquots of plasma from remainder EDTA samples for haematological investigations were frozen. Samples were then dispatched on dry ice to the laboratories being correlated. At an agreed date and time correlation samples were thawed and plasma ammonia measured. Results Passing-Bablok regression analysis showed slopes ranging from 1.00 to 1.10 and y-intercepts ranging from − 10 μmol/L to 1 μmol/L. Conclusions Despite the absence of a reference method or reference material and troublesome pre-analytical effects in ammonia measurement, plasma ammonia results from the different platforms in general compare well. The study also demonstrates that samples for ammonia measurement can be transported over great distances and still correlate well. Furthermore, a common reference interval for plasma ammonia may be a possibility.