Supplements Vitamins and Blood Tests Supplements Vitamins and Blood Tests Various blood tests are performed for checking the level of minerals and vitamins in the body. The volume of blood in human body is 6 to 7% of the body weight. That is about 4 to 5 liters for a person of 70 kg. So these blood tests are vastly altered by the amount of water that a person drinks before the blood test. But...