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Introduction ⬇

Ammonia (NH3 Level)

Ammonia, an end product of protein metabolism, is formed by bacteria acting on intestinal proteins together with glutamine hydrolysis in the kidneys. The liver normally removes most of this ammonia through the portal vein circulation and converts the ammonia to urea. Because any appreciable level of ammonia in the blood affects the body’s acid–base balance and brain function, its removal from the body is essential. The liver accomplishes this by synthesizing urea so that it can be excreted by the kidneys.

Blood ammonia levels are used to diagnose Reye syndrome, to evaluate metabolism, and to determine the progress of severe liver disease and its response to treatment. Blood ammonia measurements are useful in monitoring patients on hyperalimentation therapy.

Normal Findings ⬆ ⬇

Adults: 15–80 μg/dL or 11 to 47 μmol/L

Children older than 2 years: 19–60 μg/dL or 11–35 μmol/L

10 days to 2 years: 70–135 μg/dL or 41–80 μmol/L

Birth to 10 days: 170–340 μg/dL or 100–200 μmol/L

Values test somewhat higher in capillary blood samples. Values can vary with testing method used.

Procedure ⬆ ⬇

  1. Obtain a 5-mL venous plasma sample from a fasting patient. A green-topped (heparin) or purple-topped (EDTA) tube may be used. Observe standard precautions.

  2. Place the sample in an iced container. The specimen must be centrifuged at 4 °C. Promptly remove plasma from cells. Perform the test within 20 minutes or freeze plasma immediately.

  3. Note all antibiotic drugs the patient is receiving; these drugs lower ammonia levels.

Clinical Implications ⬆ ⬇

Increased ammonia levels occur in the following conditions:

  1. Reye syndrome (a potentially fatal disease associated with aspirin use secondary to viral infections primarily in children)

  2. Liver disease, cirrhosis

  3. Hepatic coma (does not reflect degree of coma)

  4. GI hemorrhage

  5. Kidney disease

  6. HHH syndrome: hyperornithinemia, hyperammonemia, homocitrullinuria

  7. Transient hyperammonemia of newborn

  8. Certain inborn errors of metabolism of urea except for argininosuccinic aciduria

  9. GI tract infection with distention and stasis

  10. Total parenteral nutrition

  11. Ureterosigmoidostomy

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure. Instruct the patient to fast (if possible) for 8 hours before the blood test. Water is permitted.

  2. Do not allow the patient to smoke for several hours before the test (raises levels).

  3. Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Begin treatment.

  2. In patients with impaired liver function demonstrated by elevated ammonia levels, the blood ammonia level can be lowered by reduced protein intake and by use of antibiotic drugs to reduce intestinal bacteria counts.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Clinical Alert

Ammonia should be measured in all cases of unexplained lethargy and vomiting, with encephalitis, or in any neonate with unexplained neurologic deterioration

Interfering Factors ⬆

  1. Ammonia levels vary with protein intake and many drugs.

  2. Exercise may cause an increase in ammonia levels.

  3. Ammonia levels may be increased by use of a tight tourniquet or by tightly clenching the fist while samples are drawn.

  4. Ammonia levels can rise rapidly in the blood tubes.

  5. Hemolyzed blood gives falsely elevated levels.