After an overnight fast (no food intake), you are given 50 grams of flavored liquid containing lactose to drink. After a defined period of time, tests are performed to determine whether your body can break down the lactose and absorb it.
The preferred, non-invasive method is the measurement of breath hydrogen content. In this method, breath samples are collected as you exhale. The exhaled gases are analyzed for hydrogen, a byproduct of bacteria that breakdown the lactose that is not absorbed.
If this test is not available, blood samples can be taken at various time to measure the amount of glucose, a product of lactose breakdown, in your blood. These blood samples are taken immediately prior to the test and then at various times after drinking the lactose solution (usually 30, 60, and 120 minutes).
Blood collection (Adult or child): Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Blood collection (Infant or young child): The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
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