Ammonia

Also written as: NH3, Plasma ammonia

A waste product of protein breakdown that a healthy liver clears almost completely.

What it measures

The level of ammonia in blood. Ammonia is produced when the body and gut bacteria break down protein, and the liver normally converts it into urea for the kidneys to excrete, keeping the blood level low.

Why a doctor orders it

It is most often ordered when confusion or reduced alertness is being evaluated in someone with known liver disease. It is also used to monitor certain medications, valproate in particular, and in the workup of rare inherited disorders of protein metabolism, mostly in infants and children.

What is generally associated with a higher result

Broadly associated with advanced liver disease, conditions that shunt blood past the liver, gastrointestinal bleeding, certain medications including valproate, and rare inherited urea cycle disorders. It is also one of the values most often raised falsely by how the sample was collected and handled, so an unexpected result is frequently a laboratory artifact.

What is generally associated with a lower result

A low ammonia is not generally considered meaningful.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

Sample handling - the tube needs to go on ice and be processed quickly, or the value climbs on the bench
A tight tourniquet or fist clenching during the draw
Strenuous exercise before the draw
Smoking shortly before the draw
A high-protein meal beforehand

Questions to take to your appointment

Was the sample kept on ice and processed promptly?
Does this number match how I have actually been thinking and functioning?
Could a medication such as valproate be playing a role?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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