Ammonia Blood Test-Introduction, Test Result, Unit, Reference Range, Test Methods, Clinical Significance, and Keynotes

Introduction

n ammonia blood test is used to measure the level of ammonia in the blood. It is typically performed to detect hyperammonemia, which is a higher than expected level of ammonia​​. Ammonia is produced when proteins are broken down by bacteria in the intestines and is usually converted into urea by the liver, which is then excreted in urine​.

This test is utilized to assist in diagnosing high ammonia levels in individuals exhibiting symptoms. Although it does not alone diagnose conditions that cause elevated ammonia levels, it is often used in conjunction with other tests to determine the underlying cause​​.

One of the primary uses of the ammonia blood test is to diagnose and monitor hepatic encephalopathy, which is a severe liver disease. The normal range for ammonia in the blood is 15 to 45 µ/dL (11 to 32 µmol/L), but this can vary slightly among different laboratories​.

Test Result, Unit, Reference Range, and Test Methods

The ammonia blood test measures the level of ammonia in the blood using a photometric method with Bromophenol Blue.​ The test is performed on Plasma EDTA as the specimen type​. The process involves a patient specimen being spread on a slide to distribute it evenly, with ammonia in the sample reacting with an indicator in the second reagent layer, and the density of the dye is measured after a fixed incubation period​³​.

The reference range for this test is less than or equal to 30 mcmol/L​​. It’s important to note that plasma ammonia concentrations don’t correlate well with hepatic encephalopathy and can be elevated due to increased dietary protein intake​⁵​. For newborns younger than one week, values less than or equal to 82 mcmol/L are considered normal​⁵​.

The test typically requires 0.5 mL or more of plasma, which should be put on ice immediately after collection, centrifuged at refrigerated temperature, and the plasma should be frozen within 2 hours of collection​³​. The stability of the specimen is up to 7 days when frozen and 2 hours when refrigerated​​.

Proper specimen handling is crucial as false increases in ammonia can occur if the instructions for transport and processing are not strictly followed​⁷​. The test is performed every day at Mayo Clinic Laboratories, and the results are typically available the same day or within 1 day​​. All specimens are evaluated for test suitability​.

Clinical Significance

The clinical significance of the ammonia blood test lies in its ability to indicate severe liver dysfunction. Elevated levels of ammonia are associated with conditions such as hepatic encephalopathy, coma due to cirrhosis, severe hepatitis, Reye’s syndrome, and drug hepatotoxicity​¹​. These conditions can seriously affect metabolic processes, particularly protein metabolism, of which ammonia is a by-product. The test’s results, especially when elevated, can prompt further diagnostic procedures and interventions to address these potentially life-threatening conditions.

Keynotes

Keynotes on the ammonia blood test include:

1. Purpose: It measures the ammonia level in the blood, primarily to check for liver dysfunction like hepatic encephalopathy.
2. Specimen: Plasma EDTA is used, requiring proper handling and refrigeration immediately after collection.
3. Method: A photometric technique with Bromophenol Blue is typically employed.
4. Reference Range: Normal values are generally ≤30 mcmol/L, but they can be higher in newborns.
5. Clinical Significance: Elevated ammonia can indicate serious liver issues such as cirrhosis, hepatitis, or Reye’s syndrome.
6. Test Handling: The specimen must be on ice post-collection and processed correctly to avoid false results.
7. Turnaround: The test is performed daily with results usually available within the same day or 1 day.

Further Readings

1. Medical journals such as the “Journal of Hepatology” or “Liver International” often publish studies and reviews on ammonia metabolism and its clinical implications.
2. Textbooks on clinical biochemistry or laboratory medicine usually contain detailed sections on the biochemistry of ammonia and the methodologies for its measurement.
3. The Mayo Clinic or Quest Diagnostics websites provide patient-centered information on the test, including preparation, what to expect, and interpretation of results.
4. MedlinePlus, a service of the National Library of Medicine, offers a comprehensive overview and links to additional resources.
5. Articles on eMedicine from Medscape provide information on conditions associated with abnormal ammonia levels and the role of the ammonia blood test in clinical diagnostics.