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 (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 airtight 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. Alternatively, an intravenous catheter or a small needle called a butterfly may be placed in the arm or hand to minimize the number of needle sticks.
Three blood specimens are taken. The first is collected between 6 and 8 a.m. Then you are asked to drink a water solution with 75 grams of glucose. You may be advised to drink this slowly to avoid becoming nauseated. However, the solution must be consumed within 5 minutes or the test results may be altered.
The second and third blood samples are collected 1 to 2 hours after you finish drinking the glucose solution. Each sample should be taken to the laboratory immediately. Glucose and hGH are measured in each sample.
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