Laboratory Blood Test: What It Is, Why It Is Done, and How to Prepare

This test is a laboratory analysis that measures specific substances in your body, such as blood cells, chemicals, proteins, hormones, or other markers, to help your healthcare provider evaluate your overall health or check for a particular medical condition.

The 24-hour urine ammonia nitrogen test measures how much ammonia nitrogen your kidneys excrete in a 24-hour period. Ammonia is a waste product created when your body breaks down proteins. Your liver normally converts ammonia into urea, which is then filtered from your blood by your kidneys and excreted in urine. This test helps doctors see how well your kidneys and liver are working together to remove this waste.

Your provider may order this test to help diagnose a health problem, monitor an ongoing condition, see how well a treatment is working, or screen for potential issues before symptoms appear, so that the right decisions about your care can be made.

Your doctor may order this test if you have symptoms of kidney or liver problems, such as swelling in your legs, yellowing of your skin or eyes, unusual fatigue, or changes in urination. It may also be used to monitor certain metabolic conditions, evaluate kidney function after a transplant, or check for urinary tract infections that affect ammonia processing.

Preparation depends on the specific test your provider ordered. You may be asked to fast for 8 to 12 hours, avoid certain foods, drinks, supplements, or medications, and drink plenty of water. Always follow the exact instructions your healthcare team gives you.

Before the test, tell your doctor about all medications you take, as some medicines can affect ammonia levels. You may need to avoid certain foods like meat, fish, eggs, and dairy for 24-48 hours before the test, as these can increase ammonia production. Avoid intense exercise during the collection period, as it can affect test results. Your doctor will provide specific instructions about fasting and medication adjustments.

A trained professional will usually draw a small sample of blood from a vein in your arm using a thin needle, or collect a urine or swab sample if the test requires it. The procedure is quick, and you may feel a brief sting or pinch during collection.

You will receive one or more special containers from the laboratory. On the morning of collection, start by urinating into the toilet and noting the exact time. For the next 24 hours, collect all urine in the provided container. Keep the container refrigerated or in a cool place. At the exact same time the next morning, urinate into the container one last time to complete the collection. Return the container to the lab as soon as possible.

Your results are compared with standard reference ranges. Values that are higher or lower than normal may suggest an infection, a deficiency, inflammation, or another condition, but only your healthcare provider can interpret them accurately along with your symptoms and medical history.

Normal results vary by laboratory, but generally range from 20 to 70 millimoles per 24 hours. Higher than normal ammonia levels may indicate kidney problems, liver disease, urinary tract infection, or a metabolic disorder. Lower than normal levels are less common but may occur with certain genetic conditions. Your doctor will interpret your results based on your symptoms, medical history, and other test results.