This test is used to determine if a patient has kidney disease .
Vitamin D has to be activated by adding hydroxyl groups before it becomes a hormone.
A second hydroxylation takes place in the kidneys. 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 . Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.