DefinitionKetones are substances produced when fat cells break down in the blood. A serum ketone test is a measurement of how many ketones are in the blood.Alternative NamesAcetone bodies; Ketones - serum; Nitroprusside test; Ketone bodies - serum; Ketones - bloodHow the test is performedBlood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.Once the blood has been collecte