At Home Ammonia Monitoring of Inborn Errors of Ammonia Metabolism

Ammonium (NH4+, ion in aqueous solution) exists in equilibrium with ammonia (NH3, gas) according to the equilibrium reaction: NH3+ + H+ ↔ NH4+, which has a pKa of 9.25.[1] Total ammonia is the sum of all ammonium ions (NH4+) and ammonia gas (NH3) present. At the physiologically relevant pH of blood (~7.4), the ammonium/ammonia equilibrium is almost completely shifted to NH4+.[2] Total ammonia is colloquially referred to as ammonia in clinical medicine and clinical chemistry. Thus, the term ammonia in this document refers to total ammonia unless otherwise specified.

Ongoing metabolic processes in the human body continuously generate ammonia.[1,3-8] Ammonia is produced in all tissues of the body, mainly by the process of transamination followed by deamination, from biogenic amines and amino groups of nitrogenous bases (e.g., purines, pyrimidines), and within the intestine by intestinal bacterial flora through the action of urease on urea.[1, 7] Much of the ammonia produced in the intestine travels to the liver via the portal circulation. Ammonia produced by the kidneys variably clears the body in urine or enters the systemic circulation via the renal veins.[7-9]

Ammonia levels within an individual are highly dynamic over the course of a day based on dietary and exercise status.

Because of the dynamic ongoing metabolic cellular processes that generate and dispose of ammonia, accurate measurement of ammonia can be challenging; cellular components in blood may continue to create ammonia after the blood is drawn, amino acids may deaminate nonenzymatically or enzymatically. Blood samples should be immediately measured. If not immediately measured, then blood samples should be kept on ice and measured within 30 minutes of collection.

Ammonia is toxic to the central nervous system.[10]

Increased ammonia within the blood (hyperammonemia) may be caused by a variety of factors, including:

Conditions associated with either acute or chronic liver dysfunction, including, but not limited to:

Non-viral hepatitis (e.g., autoimmune hepatitis, alcoholic hepatitis, drug-induced hepatitis, ischemic hepatitis) Viral hepatitis (e.g., A, B, C, D, E, cytomegalovirus (CMV), Epstein-Barr virus (EBV) rubella (measles)) Reye's syndrome Cirrhosis End Stage Liver Disease

Certain inborn errors of metabolism including, but not limited to:

Urea cycle disorders Organic acidemias Fatty acid oxidation disorders Gastrointestinal bleeding Certain infections (including those caused by urease-producing bacteria)

Various medications, including, but not limited to:

Valproic acid Topiramate Carbamazepine Measurable changes in cognition may be associated with hyperammonemia. With either acute or chronic liver dysfunction, hepatic encephalopathy or hepatic coma may occur with hyperammonemia.

With an inborn error of metabolism affecting ammonia metabolism, a hyperammonemic crisis may occur with hyperammonemia.

Ammonia levels may increase with increasing dietary protein intake. Ammonia levels can vary throughout the day.

This Ammonia Device consists of a reusable instrument and a single-use cartridge based system that accepts a single drop of whole blood. It operates on the photometric method. The System measures the color change of a dye in the Cartridge in response to the amount of ammonia in a fixed volume of sample. Ammonia Device system. This is an investigational use only device and the performance characteristics of this product have not been established.

[ 1 ] Adeva, M. M.; Souto, G.; Blanco, N.; Donapetry, C. Ammonium metabolism in humans. Metabolism 2012, 61 (11), 1495-1511. DOI: 10.1016/j.metabol.2012.07.007.

[ 2 ] Bates, R. G.; Pinching, G. D. Acidic Dissociation Constant of Ammonium Ion at 0 to 50°C and the Base Strength of Ammonia. Journal of Research of the National Bureau of Standards 1949, 42, 419-430. DOI: 10.6028/jres.042.037.

[ 3 ] Patel, R.; Kaemingk, B. D.; Carey, W. A.; Block, D. R.; Madigan, T. Proposed Plasma Ammonia Reference Intervals in a Reference Group of Hospitalized Term and Preterm Neonates. The Journal of Applied Laboratory Medicine 2020, 5 (2), 363-369. DOI: 10.1093/jalm/jfz001.

[ 4 ] Berry, S. A.; Lichter-Konecki, U.; Diaz, G. A.; McCandless, S. E.; Rhead, W.; Smith, W.; LeMons, C.; Nagamani, S. C. S.; Coakley, D. F.; Mokhtarani, M.; et al. Glycerol phenylbutyrate treatment in children with urea cycle disorders: Pooled analysis of short and long-term ammonia control and outcomes. Molecular Genetics and Metabolism 2014, 112 (1), 17-24. DOI: 10.1016/j.ymgme.2014.02.007.

[ 5 ] Häberle, J.; Burlina, A.; Chakrapani, A.; Dixon, M.; Karall, D.; Lindner, M.; Mandel, H.; Martinelli, D.; Pintos-Morell, G.; Santer, R.; et al. Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision. Journal of Inherited Metabolic Disease 2019, 42 (6), 1192-1230. DOI: 10.1002/jimd.12100.

[ 6 ] Lee, B.; Diaz, G. A.; Rhead, W.; Lichter-Konecki, U.; Feigenbaum, A.; Berry, S. A.; Le Mons, C.; Bartley, J. A.; Longo, N.; Nagamani, S. C.; et al. Blood ammonia and glutamine as predictors of hyperammonemic crises in patients with urea cycle disorder. Genet Med 2015, 17 (7), 561-568. DOI: 10.1038/gim.2014.148 From NLM.

[ 7 ] Weiner, I. D.; Hamm, L. L. Molecular mechanisms of renal ammonia transport. Annu Rev Physiol 2007, 69, 317-340. DOI: 10.1146/annurev.physiol.69.040705.142215.

[ 8 ] Levitt, D. G.; Levitt, M. D. A model of blood-ammonia homeostasis based on a quantitative analysis of nitrogen metabolism in the multiple organs involved in the production, catabolism, and excretion of ammonia in humans. Clin Exp Gastroenterol 2018, 11, 193-215. DOI: 10.2147/CEG.S160921.

[ 9 ] Mohiuddin, S. S.; Khattar, D. Biochemistry, Ammonia. In StatPearls, 2025. [ 10 ] Balistreri, W.; Rej, R. Liver Function. In Tietz Fundamentals of Clinical Chemistry. 4th ed.Philadelphia, Burtis, C., Ashwood, E. Eds.; WB Saunders, 1996; pp 539-568.