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Methylmalonic acid 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.
How to Prepare:
Adult:
No special preparation is necessary.
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:
How it Feels:
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 .
Risks:
- 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
Why this Test is Performed:
This test is used to look for methylmalonic acid which, when present, may signify certain genetic disorders.
Normal Values:
Methylmalonic acid is not detected by usual procedures.
Sensitive laboratories may detect small quantities (19 to 76 ng/ml).
Note: ng/ml = nanograms per milliliter
Abnormal Results:
Cost:
The estimated cost is $63.
Special Considerations:
Two enzymes are involved in the conversion of propionyl CoA (formed from amino acid metabolism ) to methylmalonyl CoA. In addition, biotin and cobalamin are needed as cofactors. Inherited deficiencies of the necessary enzymes cause metabolic ketoacidosis requiring protein restriction and treatment with bicarbonate in the neonatal period.
Normally methylmalonic acid and its precursor (propionic acid) are found in very small amounts in body fluids because methylmalonyl CoA is converted to succinyl CoA, which is further metabolized to produce energy or is involved in the synthesis of porphyrins. When methylmalonyl CoA builds up to an abnormal level, an enzyme that converts it to methylmalonic acid becomes active.
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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