Liver function tests, commonly known as LFTs, are a group of blood tests that assess liver health and function. They measure specific enzymes, proteins, and other substances produced or processed by the liver. Healthcare providers use LFTs to screen for liver infections, monitor existing liver conditions, evaluate the effectiveness of treatments, and check for potential side effects of certain medications. Abnormal levels in these tests can indicate liver damage or disease.
The Right Tube for Liver Function Tests
Liver function tests primarily require a blood sample that yields serum, the liquid portion of blood after clotting. For this reason, the most commonly used blood collection tube for LFTs is the Serum Separator Tube (SST). These tubes are often identified by a gold-colored stopper or a red-gray “tiger top” stopper.
SSTs contain specific additives that facilitate the separation of serum. They typically have a clot activator, which speeds up the blood clotting process. After the blood clots, a special gel separator within the tube forms a stable barrier. This gel moves during centrifugation, creating a physical division between the heavier clotted blood cells and the lighter serum. This clean separation ensures that the liquid serum, containing the enzymes and proteins measured in LFTs, is easily accessible for laboratory analysis.
Preparing for Your Liver Function Test
Preparation for LFTs often involves specific guidelines from your healthcare provider. While not all LFT components require fasting, it is often recommended or required for accurate results, especially if other blood tests are done simultaneously. Fasting typically means refraining from food and drinks, other than water, for 8 to 12 hours before the blood draw.
Discuss all medications, including over-the-counter drugs and supplements, with your doctor before the test. Some medications can influence liver function and affect test results, so your doctor will advise whether to continue or temporarily stop certain ones. Staying well-hydrated by drinking water is generally encouraged, as it can make veins more visible and accessible, making the blood collection process smoother.
What to Expect During Blood Collection
Blood collection, known as phlebotomy, is a routine procedure. A healthcare professional will typically ask you to extend your arm, usually selecting a vein in the elbow bend or on the back of your hand. They will clean the chosen area with an antiseptic solution to prevent infection.
A soft band, called a tourniquet, is placed around your upper arm to make veins more prominent. You may feel a brief pinch or sting as the small needle is inserted. Blood flows into collection tubes, and the process usually takes only a few minutes. Once enough blood is collected, the tourniquet is removed, and the needle withdrawn. Pressure is applied to the site with gauze or cotton, and a bandage placed to stop bleeding.