Ammonia

Ranges vary between labs (some print up to 35, others up to 55) and are higher in newborns; use the range printed.

Ammonia is made when the gut and the body break down protein. A healthy liver converts it into urea, which the kidneys pass into the urine, so very little stays in the blood. The test measures the amount in a blood sample and is a guide to how well the liver is clearing it.

Doctors request it mainly in hospital when someone with liver disease becomes confused or drowsy, in some rare inherited conditions of protein handling, and occasionally when looking into unexplained confusion. It is rarely part of a routine panel.

• Advanced liver disease
• Bleeding into the gut, which is digested as protein
• Some medicines, including sodium valproate
• Rare inherited conditions of the urea cycle
• Very hard exercise, for a short time
• Smoking or a delayed, warm or haemolysed sample

• It has no meaningful lower limit; low values are the usual state in the general population
• Some antibiotics that reduce gut bacteria
• Lactulose and other medicines used in liver disease

• The commonest reason for a raised value in the general population is a sample problem: the tube must be taken on ice and reach the lab within minutes
• A tight tourniquet, fist clenching or smoking shortly before raises it
• Very hard exercise raises it for an hour or two

Needs a special tube, taken without a tourniquet if possible, placed on ice and sent straight to the lab. A result from a delayed sample is not reliable.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.