LDH isoenzymes
Alternative names:
lactate dehydrogenase isoenzymes; lactic dehydrogenase isoenzymes; LD1; LD2; LD3; LD4; LD5; LDH1; LDH2; LDH3; LDH4; LDH5
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 for the test:
The health care provider may advise you to withhold drugs that may affect the test (see special considerations).
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 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 usually performed when LDH levels are elevated. Measurement of LDH isoenzymes is helpful to differentiate the source (location) of tissue damage.
The enzyme LDH is in many body tissues especially heart, liver, kidney, skeletal muscle, brain blood cells, and lungs. LDH catalyzes the interconversion of pyruvate and lactate.
LDH exists in 5 forms, called isoenzymes, which differ slightly in structure. LDH-1 is in highest concentrations in heart muscle and red blood cells. LDH-2 is highest in white blood cells. LDH-3 is highest in the lung. LDH-4 is highest in the kidney, placenta, and pancreas. LDH-5 is highest in the liver and skeletal muscle. All of these isoenzymes can be measured in the blood.
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