Ammonia Blood Test: Levels, Causes & Symptoms

Understanding the Ammonia Blood Test

When a patient arrives in my clinic with sudden confusion, slurred speech, or unexplained fatigue, one of the first tests I consider is a blood ammonia level. Ammonia is a natural byproduct of protein digestion and bacterial activity in the gut. Under normal circumstances, your liver efficiently converts it into harmless urea, which is then excreted by the kidneys. However, when liver function is compromised, ammonia can build up in the bloodstream, potentially leading to a serious condition known as hepatic encephalopathy.

What does an ammonia blood test measure?

This test measures the concentration of ammonia in your blood, specifically in micromoles per liter (µmol/L). It is a direct indicator of how well your liver is detoxifying this waste product. In my clinical practice, I often see this test used alongside other liver function tests to paint a complete picture of hepatic health.

Why might my doctor order an ammonia test?

I typically order an ammonia test when a patient shows neurological symptoms that could point to toxin buildup, such as in advanced liver cirrhosis or acute liver failure. It is also crucial for monitoring patients with known liver disease, evaluating newborns with lethargy and vomiting (to rule out urea cycle disorders), and assessing the cause of unexplained coma.

Normal Ammonia Reference Ranges

Interpretation of ammonia levels is highly age-dependent. What is normal for a newborn is not normal for an adult. The following table provides a general guide, though ranges can vary slightly between laboratories.

Is high ammonia level dangerous?

Yes, elevated ammonia, or hyperammonemia, is a medical concern. Ammonia is toxic to the brain. My patients with significantly high levels often experience progressive confusion, drowsiness, and in severe cases, can slip into a coma. This is a key feature of hepatic encephalopathy in liver disease and requires prompt intervention.

What are the symptoms of high ammonia levels?

Symptoms often begin subtly. Patients may report mental fogginess, forgetfulness, or a slight tremor. As levels rise, this can escalate to obvious confusion, slurred speech, clumsiness, and excessive sleepiness. In infants, poor feeding, vomiting, and lethargy are common red flags.

Can ammonia levels be too low?

Clinically low ammonia levels are very rare and are usually not a cause for concern. They may occasionally be seen with certain medications, like antibiotics that gut bacteria, or in cases of severe malnutrition. In practice, we focus far more on the implications of high levels.

Causes of Abnormal Ammonia Levels

Common causes of high ammonia (Hyperammonemia)

The vast majority of cases I manage are linked to liver dysfunction. This includes chronic conditions like cirrhosis and alcoholic liver disease, as well as acute hepatitis or liver failure. Other important causes are genetic urea cycle disorders (often diagnosed in infancy), Reye's syndrome in children recovering from viral infections, and severe heart failure reducing blood flow to the liver.

Ammonia and diet: what you need to know

Diet plays a significant role in ammonia production. A very high-protein diet can increase the gut's ammonia load, which a compromised liver may struggle to handle. Conversely, in patients with liver disease, we sometimes recommend a moderated protein intake under dietitian guidance to help manage levels, though protein restriction must be balanced to prevent malnutrition.

Ammonia testing in children: special considerations

Testing in children, especially newborns, is critical for diagnosing inborn errors of metabolism like urea cycle defects. These are medical emergencies. The blood sample must be processed quickly and kept on ice, as ammonia levels can artificially rise if the sample is left at room temperature.

Diagnosis, Treatment, and Next Steps

How is high ammonia treated?

Treatment is two-fold: lowering existing ammonia and preventing further buildup. We use medications like lactulose, which acidifies the colon and traps ammonia for excretion, and antibiotics like rifaximin to reduce ammonia-producing gut bacteria. Crucially, we must treat the underlying cause, whether that's managing liver disease or addressing a metabolic disorder.

If your ammonia level is abnormal, the next step is a thorough consultation with your doctor. They will correlate the result with your symptoms, medical history, and other test findings to determine the best course of action. Management is highly individualised and often involves a specialist hepatologist or metabolic physician.