Plasma Ammonia

Specimen Required

Heparinized or EDTA Blood

Fasting Required

Purpose of the Test

To detect elevated concentrations of ammonia in the blood, to help diagnose severe liver disease and certain genetic urea cycle disorders, to investigate changes in consciousness, or to help diagnose hepatic encephalopathy and Reye’s syndrome

When this test is required

An ammonia blood test may be requested on a newborn when they are irritable, vomiting, tired, and have seizures during the first few days after birth. It may be performed when a child develops these symptoms about a week after a viral illness such as flu or a cold when the doctor suspects that the child may have Reye’s syndrome.When adults experience mental changes, disorientation, sleepiness, or lapse into a coma, an ammonia blood test may be requested to help investigate the cause of the change in consciousness. In patients with stable liver disease, an ammonia blood test may be requested, with other liver function tests, when a patient suddenly “takes a turn for the worse” and becomes more acutely ill.

What the Test Detects

This test measures the concentration of ammonia in the blood. Ammonia is a chemical produced by bacteria in the intestine and by cells in the body during the processing of proteins. Ammonia is a poisonous waste product which is normally transported to the liver, and then converted into two chemicals called urea and glutamine. The urea is then carried by the blood to the kidneys, where it is excreted in the urine. If this does not work correctly, ammonia can build up in the blood and pass into the brain.Accumulation of ammonia and other compounds normally broken down by the liver can cause a condition affecting the brain called hepatic encephalopathy. This causes symptoms such as confusion, disorientation, drowsiness, and eventually coma and even death. Infants and children with increased blood ammonia concentrations may vomit frequently, be irritable, and be increasingly tired. If left untreated, they may develop seizures, breathing difficulty, and fall into a coma.Ammonia can accumulate in the bloodstream due to several reasons, including:Rare inherited defects in the urea cycle – a deficiency or inborn genetic defect affecting one or more of the enzymes necessary to complete the conversion of ammonia to urea.Severe liver disease – damage which reduces the ability of the liver to breakdown and remove ammonia. Sudden increases in blood ammonia concentration may be seen in patients with stable liver disease, especially following an event such as a bleed into the stomach or elsewhere in the intestine or an imbalance in sodium or other electrolytes.Decreased blood flow to the liver such that ammonia is less able to be removed.Reye’s syndrome – a rapidly developing condition that affects the blood, brain, and liver. It typically produces a rise in ammonia and a fall in glucose and affects children and young adults. In most cases, it follows and appears to be triggered by a viral infection. Children who use aspirin are at an increased risk.Kidney failure – the kidneys are unable to effectively remove the body’s urea, leading to a build-up of ammonia in the blood.How is the sample collected for testing?A blood sample is obtained by inserting a needle into a vein or artery in the arm.Is any test preparation needed to ensure the quality of the sample?Samples must be sent to the laboratory prompty for analysis.

Preparation for the Test

Avoid smoking cigarettes prior to collection of the specimen and follow any other instructions that you are given

Sample Requirements

A blood sample taken from a vein or artery in your arm

Additional Notes

Increased concentrations of ammonia may also be seen with: Gastrointestinal bleeding – blood cells are haemolysed (broken apart) in the intestines, releasing protein which is digested, absorbed and converted into ammonia. Muscle exercise – muscles produce ammonia when active and absorb it when resting. Tourniquet use – ammonia can be increased in blood samples collected using a tourniquet when it has been applied for a long time. Drugs that can increase blood ammonia concentration include: alcohol, barbiturates, diuretics, valproic acid and narcotics SmokingDecreased concentration of ammonia may be seen with high blood pressure and the use of some antibiotics (such as neomycin). Ammonia tests can also be measured on blood taken from arteries, but this is rarely done although some doctors believe that arterial ammonia measurements are more useful.

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