Understanding Your Diagnostic Test: What to Expect and How to Prepare

This test is a routine medical evaluation that helps your healthcare provider assess how your body is functioning and look for signs of illness or other health concerns. It provides valuable information that supports an accurate diagnosis and helps guide decisions about your ongoing care and treatment.

The plasma ammonia test measures the amount of ammonia (NH3) in the liquid portion of your blood (plasma). Ammonia is a waste product created when your body breaks down proteins. Normally, the liver converts ammonia into urea, which is then excreted by the kidneys. This test helps healthcare providers assess how well your liver is functioning and whether your body is properly removing ammonia waste.

The test is performed by a trained member of your care team in a clinic, hospital, or laboratory setting. Depending on the type of test ordered, it may involve providing a small sample, such as blood or urine, or undergoing a simple, noninvasive procedure. Most tests take only a short time to complete, and you can usually return to your normal activities right away.

A healthcare professional will draw a blood sample from a vein in your arm using a needle. The blood is collected in a special tube containing an anticoagulant to prevent clotting. The sample must be placed on ice and processed quickly—usually within 30 to 60 minutes—because ammonia levels can increase in the sample if left standing at room temperature.

Your healthcare provider will give you specific instructions before the test, and it is important to follow them closely. You may be asked to avoid eating or drinking for several hours beforehand, or to temporarily stop taking certain medications or supplements. Wear comfortable clothing, drink water unless told otherwise, and bring a list of your current medications along with any questions you would like to ask.

Your doctor may ask you to fast (not eat or drink anything except water) for 8 to 12 hours before the test. You should also avoid smoking before the test, as smoking can increase ammonia levels. Inform your doctor about all medications you are taking, as certain drugs (such as diuretics, valproic acid, or lactulose) can affect test results. Your doctor may instruct you to temporarily stop taking specific medications.

Your results will be compared with established reference ranges to show whether your values fall within the expected range. Normal results generally suggest that no abnormalities were detected, while results outside the typical range may point to a condition that needs further evaluation. Your healthcare provider will review the findings with you, explain what they mean in the context of your overall health, and recommend any follow-up testing or treatment if needed.

Normal ammonia levels vary slightly by laboratory but are typically between 15-45 μmol/L (micrograms per deciliter). High ammonia levels (hyperammonemia) may indicate liver disease, liver failure, hepatic encephalopathy, Reye's syndrome, or certain metabolic disorders. Low levels are less common but can occur with certain genetic conditions or the use of certain medications.