Finding the right tests…
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Finding the right tests…
Biochemistry
This is the same ammonia test used to investigate hepatic encephalopathy and, in infants, suspected urea cycle disorders, but the catalogue lists it separately because of what the specimen itself demands. Ammonia leaks out of red blood cells soon after blood is drawn, and if the sample sits before the plasma is separated from the cells, that leakage can push the measured level up well above what's actually circulating in your body. Because of that, this test specifically calls for plasma, blood collected with an anticoagulant and spun down promptly, rather than the serum sample used for most routine blood chemistry, and the sample is generally kept chilled from the moment it's drawn until it reaches the lab.
The result is an ammonia concentration from plasma, reported the same way as a standard ammonia test, compared against an age-adjusted expected range rather than one fixed number. What differs is entirely at the specimen-handling stage: published research comparing anticoagulants for this test has found EDTA-treated plasma gives more consistent, reliable results than heparin-treated plasma, and that keeping the sample cold and processing it quickly measurably reduces false elevation coming from the specimen itself rather than from your body.
Few common blood tests are as sensitive to how the sample is handled after it leaves your arm as ammonia is. Red blood cells contain ammonia-related compounds, and once blood is drawn, those cells continue low-level metabolic activity that releases extra ammonia into the surrounding fluid, a process that has nothing to do with your actual ammonia level and everything to do with time and temperature.
Separating plasma from blood cells promptly stops that ongoing leakage from continuing to add ammonia to the sample after collection. Published research on this has shown that plasma kept chilled reads closer to the true value than plasma left at room temperature for the same stretch of time, and that samples frozen quickly stay more stable for later analysis than samples simply kept in a refrigerator.
Among the common anticoagulants used to keep a blood sample from clotting, research comparing them for ammonia testing found EDTA-anticoagulated plasma gave noticeably more precise, reproducible results than heparin, which showed much greater sample-to-sample variability, likely from interfering substances. That's why a lab specifically requesting an ammonia plasma sample, rather than a routine serum tube, is following specimen-handling evidence built around this particular test, not an arbitrary label. The clinical reasons for ordering it are identical to a standard ammonia test; what changes is purely how the sample needs to travel from your arm to the lab.
Ammonia leaks out of red blood cells after collection, and research shows properly handled plasma, separated and chilled promptly, gives a more accurate reading than a routine serum sample.
Yes, based on published comparisons. EDTA-anticoagulated plasma has shown more consistent, reproducible ammonia results than heparin-treated plasma in specimen-handling studies.
Ongoing low-level activity in blood cells can keep releasing ammonia into the sample after it's drawn, artificially raising the result the longer processing is delayed.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
No. It measures the same thing for the same reasons; the difference is entirely in how the specimen is collected and handled to keep the result accurate.
Keeping the sample cold slows the metabolic activity in blood cells that would otherwise release extra ammonia into the plasma before testing.
Yes — the centre can tell you whether an order is for standard ammonia or specifically for ammonia plasma, and either way, the collection and handling will follow what that specific test requires.