Doctors perform liver function tests by obtaining a blood sample from the patient in a hospital or specialized testing facility, explains Healthline. A nurse cleans the patient's skin prior to the test to prevent contamination by microorganisms and then wraps a pressure device, such as a cuff, on the arm.
Wrapping a pressure device around the arm helps improve the visibility of the veins, states Healthline. The nurse draws several blood samples from the arm using a needle. Afterward, she puts gauze and a bandage over the punctured area and sends the blood samples to a laboratory for testing.
Before a liver function test, doctors provide instructions on how to prepare for the test, particularly information on which medications to stop taking for a specific period, notes Healthline. Patients should wear clothing with sleeves that are easy to roll up, allowing the nurse to gather blood samples easily. After the test, individuals can return to normal activities immediately. However, those who experience faint or lightheadedness while the nurse draws blood should rest first before going home.
Liver function tests help doctors assess the organ's health by measuring the blood's protein, enzyme or bilirubin levels, says Healthline. The albumin test, the most common liver function test used by physicians, measures the liver's ability to produce the protein albumin. Normal levels for this test range from 3.5 to 5 grams per deciliter.