Hyperammonemia

Introduction Hyperammonemia refers to an increase in blood ammonia concentration caused by a disorder of urea synthesis when liver function is severely damaged. The normal value is 27-82 mol/L (46-139 g/dl), and the blood ammonia is usually 234.8-587 mol/L (400-1000 g/dl) in this disease.

Cause

Causes:

The blood ammonia is usually 234.8 to 587 mol/L (400 to 1000 g/dl), and the normal value is 27 to 82 mol/L (46 to 139 g/dl). When hyperammonemia is coma, blood ammonia can be as high as 352.2 to 1526.2 mol/L (600 to 2600 g/dl).

The protein that is ingested daily by the human body can be decomposed and digested in the intestine to produce a certain amount of ammonia. Ammonia is a toxic substance, but after the action of liver urea synthase, urea is synthesized to remove toxicity. The urea synthase contained in this process contains biotin components. If the biotin is insufficient in the body, the enzyme activity is decreased, and the ammonia cannot be smoothly metabolized, it can cause hyperammonemia.

an examination

Related inspection

Blood ammonia

1. Increased blood ammonia

The blood ammonia is usually 234.8 to 587 mol/L (400 to 1000 g/dl), and the normal value is 27 to 82 mol/L (46 to 139 g/dl). When hyperammonemia is coma, blood ammonia can be as high as 352.2 to 1526.2 mol/L (600 to 2600 g/dl).

2. Amino acid quantitative analysis

Check blood and urine amino acids to determine if there is any specific increase. Particular attention should be paid to the quantitative analysis of glutamic acid, glutamine, alanine, citrulline, arginine and arginyl amber urine to distinguish enzyme defects in the urea cycle.

3. Protein load test

When the urea cycle is disordered, it is intolerant to protein food, and can be used for protein load test for clinical diagnosis and heterozygote detection. Naturally eat breakfast, give protein 1g / kg, observe blood ammonia and blood, urine amino acid and orotic acid changes, measured every 2 hours, a total of 3 times.

4. Blood glucose measurement, blood gas analysis, organic acid in urine

Respiratory alkalosis is common in urea cycle disorders. Organic aciduria is also often associated with hyperammonemia, but unlike urea cycle disease, due to lower blood sugar, metabolic acidosis, and the release of specific organic acids in the urine.

5. Determination of enzyme activity

Hyperammonemia caused by lack of carbamyl phosphate synthase (CPS) activity requires transcutaneous liver biopsy to determine CPS activity. The diagnosis of ornithine carbamoyltransferase (OTC) deficiency also requires measurement of hepatocyte OTC activity. The diagnosis of citrullinemia should determine whether the activity of argininosuccinate synthetase (AS) is lacking, and enzymes of hepatocytes or skin fibroblasts can be used at this time. In the case of argininosuccinate, the activity of spermaminosuccinate lyase (AL) in hepatocytes, peripheral red blood cells, and skin fibroblasts can be measured. When suspected of arginine, the activity of liver, red blood cells, and leukocyte arginase should be measured.

6. Genetic analysis

OTC deficiency and CPS deficiency can be diagnosed by molecular genetic methods for DNA diagnosis.

7. Heterozygous detection

Can be based on family analysis, protein load test, genetic analysis or enzyme activity check.

8. EEG examination has abnormal brain waves. Brain CT examination is performed when conditions are met. Other routine examinations include B-ultrasound and X-ray examination.

Differential diagnosis

Hyperammonemia needs to be differentiated from the following symptoms:

1. Neonatal transient hyperammonemia (neonatal transient hyperammonemia) is mainly seen in premature infants. Patients with extremely high blood ammonia have early symptoms, severe neurological depression and difficulty breathing. If early hemodialysis, the symptoms can be relieved within 5 days, and the prognosis is good. Asymptomatic hyperammonemia can also be seen in low birth weight infants for unknown reasons.

2. Organic acidurias are often associated with hyperammonemia. Its characteristics are: normal amino acid quantitation, low uric acid, high specific organic acids in the urine, low blood sugar, increased blood glycine, and metabolic acidosis.

3. Lysinuric protein intolerance is associated with hyperammonemia. Due to the transport defects of arginine, lysine and ornithine in the renal tubules and intestinal epithelium, the increase of the above amino acids in the blood affects the metabolic function of the urea cycle.

4. Hyperammonemia - hyperornithemia - hyperammonemia hyperonithinemia homocitrullinuria, that is, HHH syndrome, is a barrier to ornithine transport into the mitochondria.

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