Plasma ammonia

Hyperargininemia. This defect is characterized by elevated blood and cerebrospinal fluid arginine levels, low erythrocyte levels of arginase (reaction 5, Figure 29-9), and a urinary amino acid pattern resembling that of lysine-cystinuria. This pattern may reflect competition by arginine with lysine and cystine for reabsorption in the renal tubule. A low-protein diet lowers plasma ammonia levels and abolishes lysine-cystinuria. 

Deficiency of the muscle-specific myoadenylate deaminase (MADA) is a frequent cause of exercise-related myopathy and is thought to be the most common cause of metabolic myopathy. MADA catalyzes the deamination of AMP to IMP in skeletal muscle and is critical in the purine nucleotide cycle. It is estimated that about 1-2% of all muscle biopsies submitted to medical centers for pathologic examination are deficient in AMP deaminase enzyme activity. MADA is 10 times higher in skeletal muscle than in any other tissue. Increase in plasma ammonia (relative to lactate) after ischemic exercise of the forearm may be low in this disorder, which is a useful clinical diagnostic test in patients with exercise-induced myalgia... 

Transient, mild increases in liver enzyme levels, up to three times the upper limit of normal, do not necessitate discontinuation of valproate. Although y-glutamyltransferase levels are often checked by clinicians, these levels are often increased, without clinical significance, in patients receiving valproate and carbamazepine (Dean and Penry 1992). Likewise, plasma ammonia levels are often increased transiently during valproate treatment, but this finding does not necessitate interruption of treatment (Jaeken et al. 1980). Increases in transaminase levels are often dose dependent. If no... 

For plasma ammonia levels, whole blood was centrifuged and plasma pipetted into ammonia-free tubes. The plasma was then frozen immediately and kept frozen until ammonia was measured by an autoanalyzer. Urea nitrogen in the plasma and creatinine excretion in the urine were also measured by the autoanalyzer. Lactic dehydrogenase activity in the plasma was measured by a method published by Bergmeyer, Bernt, and Hess (10). Rlbonucle-ase activity was ascertained by a modified Seklne method (11,... 

One unexpected finding was that the plasma ammonia level appeared to increase as a result of zinc deficiency. We have reported similar findings in zlnc-deflclent rats (16). This may have important health implications concerning zinc deficiency In man, because in liver disease hyperammonemia is believed to affect the central nervous system adversely. 

Evaluate for urea cycle disorders, as hyperammonemic encephalopathy, sometimes fatal, has been associated with valproate administration in these uncommon disorders urea cycle disorders, such as ormithine transcarbamylase deficiency, are associated with unexplained encephalopathy, mental retardation, elevated plasma ammonia, cyclical vomiting, and lethargy... 

Hnber, M., Rossle, M., Siegerstetter, V., Ochs, A., Haag, K., Kist, M., Blnm, H.E. Helicobacter pylori infection does not correlate with plasma ammonia concentration and hepatic encephalopathy in patients with cirrhosis. Hepato-Gastroenterol. 2001 48 541 -544... 

Znllo, A., Rinaldi, V., Hassan, C., Folino, S., Winn, S., Knto, G., Attili, AJ . Helicobacter pyloric and plasma ammonia levels in cirrhotics role of urease inhibition by acetohydroxamic acid. Ital. J. Gastroenterol. Hepatol. 1998 30 405-409... 

Staedt, LL, Lewellng, H., Gladisch, R., Kortsick, C., Hagmiiller, E., Holm, E. Effects of ornithine aspartate on plasma ammonia and plasma amino acids in patients with cirrhosis. A double-blind, randomized study using a four-fold crossover design. J. Hepatol. 1993 19 424-430... 

Thus changes in the zinc concentration of plasma, erythrocytes, leucocytes, and urine and changes in the activities of zinc-dependent enzymes such as alkaline phosphatase, RNase in the plasma, and deoxythymidine kinase in the tissue during the zinc restriction phase, appear to have been induced specifically by a mild deficiency of zinc in the volunteers. One unexpected finding was with respect to plasma ammonia level which appeared to increase during the zinc-restricted period. We recently have reported a similar finding in zinc deficient rats (88). This... 

E431 Green, A. (1988). When and how should we measure plasma ammonia Ann. Clin. Biochem. 25, 199-209. 

The fasting venous plasma ammonia concentration is useful in the differential diagnosis of encephalopathy when it is unclear if encephalopathy is of an hepatic origin. It is especially helpful in diagnosing Reye s syndrome and the inherited disorders of urea metabolism. However, it is not a useful test to use in patients with laiown liver disease. 

Both enzymatic and chemical methods are used to measure ammonia in body Buids. Enzymatic assay with glutamate dehydrogenase is the most frequently used method. Plasma ammonia measurement is particularly susceptible to contamination, leading to falsely elevated concentrations. Some of the common samphng problems are discussed in the third edition of this textbook. 

The pathophysiology of hepatic encephalopathy is not completely understood but includes an increased sensitivity to dietary proteins. Ammonia concentrations are always increased with acute encephalopathy and usually increased with chronic encephalopathy. A reduction of plasma ammonia is often associated with symptomatic improvement. However, since plasma ammonia concentrations do not correlate with the severity of the encephalopathy, it has been suggested that other factors are involved. It is now recognized that a variety of neurotransmitter systems are dysfunctional in hepatic encephalopathy, but the exact cause for the changes is not known. One important contributor is the endogenous benzodiazepine agonist system, but other abnormalities must be invoked to explain all the findings. ... 

The diagnosis of hepatic encephalopathy is made on clinical grounds. Plasma ammonia concentrations are rarely helpful, either for diagnosis or for monitoring the patient s disorder normal ammonia concentrations are helpful in excluding hepatic encephalopathy as a cause of cerebral dysfunction. An exception is a patient who presents with acute encephalopathy of unknown cause. Elevated ammonia concentrations in that situation suggest acute hepatic failure or Reye s syndrome. 

The determination of plasma ammonia is of great importance both for the diagnosis and for the treatment of hereditary metabolic disorders of the urea cycle. The level is always raised in these conditions since the other mechanisms for regulating blood ammonia mentioned above are not able by themselves to keep the ammonia level within normal limits. 

The results of the determinations of blood or plasma ammonia levels are variously reported in the literature as micrograms of ammonia or jag of ammonia nitrogen per 100 ml. There is a difference of 21.4% calculated on ammonia. To avoid the necessity of recalculating all values reported so as to attain uniformity, all levels are given as ammonia, whether reported as ammonia nitrogen or not. 

Of the 11 known cases, 10 are female and 1 male. The prognosis is poor. Three have died, one in the second year of life (H5) and two in the seventh year of life (L8). On the other hand, one child, a girl aged 4 years, on a very low protein diet, is well and of normal intelligence (LIO). Another child, a boy also on a low protein intake, has developed normally and has a normal IQ (L6). Other children, although still alive, have gross mental and physical retardation (C13, L3). The only adult with this condition so far diagnosed is quite normal apart from an elevated plasma ammonia (L3). 

Hyperammonemia resulting from any of the enzymatic disorders of the biosynthesis of urea, must be distinguished from other conditions in which plasma ammonia is raised, sometimes sufficiently so to cause clinical manifestation. Severe liver disease as a primary cause of acquired hyperammonemia may be excluded from consideration since it is readily distinguishable from urea cycle defects. However, there are a number of other conditions described with hyperammonia as a prime manifestation, which because they show some clinical and biochemical similarity to hereditary enzyme defects of the urea cycle, have been claimed to be urea cycle disorders. 

Clinically the patients present with chronic progressive extra-pyramidal and cerebellar symptoms, often combined with hyperreflexia and extensor plantar reflexes. Besides motor functions, the patients cognition and consciousness may also be impaired, but are less impressive than the motor functions. The effect of the classical therapeutic interventions aimed at the lowering of plasma ammonia levels is limited in chronic persistent HE. Liver transplantation has been reported to resnlt in an improvement of the nemological symptoms (PoweU et al., 1990). Today, however, controlled studies on this snbject are missing. 

In patients who have other medical problems such as advanced liver disease with hepatic insufficiency, it is often difficult to differentiate whether the encephalopathy is due to hepatic or renal causes. In patients with renal failure, the major route for elimination of urea is not available thus, there is an ino-ease in blood urea. The amount of urea that enters the colon is ino-eased because of the elevated plasma urea. Urea is then acted on by colonic bacteria and mucosal enzymes in a manner similar to that of protein and amino acids. This leads to inCTeased ammonia production in uremic subjects that may either increase plasma ammonia levels or lead to misinterpretation of this test. 

Due to concern of the recent changes to the status of the infant, additional labs including a metabolic panel and plasma ammonia are recommended immediately. These labs show the baby is extremely acidotic as well as hyperammonemic. The infant is airlifted to a children s hospital for tertiary care by the metabolic team. However, due to the extent of the acidosis and hyperammonemia as well as the prematurity, care is terminated. 

Camilla, a newborn female, was delivered in a forceps-assisted vaginal delivery after a normal pregnancy. The infant did well for the first 3 days of life, but began showing seizure-like activity. A CT scan showed a small trauma from the forceps-assisted birth including a small bleed and skull fracture. Laboratory studies obtained showed mild metabolic acidosis and mild hyperammonemia. The infant was transferred to the children s hospital for further tertiary care. Repeat plasma ammonia showed increasing hyperammonemia. 

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