| Definition: |
A test that measures the amount of ketones in the blood. Any amount is considered abnormal.
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| Alternative Names: |
Acetone bodies; Ketones - serum; Nitroprusside test; Ketone bodies - serum
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| How the test is performed: |
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.
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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| How to prepare for the test: |
Fast for 4 hours before the test.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
| When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed: |
This test is used in the diagnosis of ketoacidosis, an acute diagnosis often made in an urgent care center of emergency department. A patient suspected of having ketoacidosis may have already had a urine test showing ketones in the urine or a blood test showing low levels of bicarbonate, indicating acid in the blood.
Ketone bodies (acetone, acetoacetic acid, beta-hydroxybutyric) are synthesized by the liver from excess fatty acids. Various tissues in the body, especially muscle, can use ketone bodies as a source of energy.
Fatty acids are released from the adipose (fat) tissue when it is stimulated by glucagon, growth hormone, and/or epinephrine. These hormones increase when serum glucose levels are low (hypoglycemia). In normal individuals this serves a useful purpose because certain tissues, especially muscle, can use the fatty acids or ketone bodies for energy in lieu of glucose (which is then saved for the tissues which survive solely on glucose, particularly the brain and red blood cells).
The main causes of significant ketosis (elevated ketone bodies) are uncontrolled diabetes, starvation, and alcoholism. These physiologic processes may lead to excess acetoacetic acid or beta-hydroxybutyric acid production, resulting in a metabolic acidosis.
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| Normal Values: |
| The usual test for ketone bodies is a qualitative test and the normal value is negative. |
| What abnormal results mean: |
| A positive test for serum ketones may indicate:
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| What the risks are: |
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
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| Special considerations: |
A diet low in carbohydrates can result in increased ketone bodies.
Urine may also be tested for the presence of ketones.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. |
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