LDH isoenzymes; Lactic (lactate) dehydrogenase isoenzymes
This is a test that measures the amount of the isoenzymes (different forms) of lactate dehydrogenase (LDH) in blood serum.
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band or blood pressure cuff is placed around the upper arm to cause veins to swell with blood.
A needle is inserted into a vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band 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.
For infants or young children:
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.)
For infants and children:
The preparation involved in readying a child for any test or procedure depends on the child’s age, interests, previous experiences, 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:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- Schoolage test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
When the needle is inserted to draw blood, some people may feel moderate pain, while others may feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test is usually performed when elevated LDH levels are suspected. Measurement of LDH isoenzymes helps determine the location of tissue damage.
The enzyme LDH is found in many body tissues like the heart, liver, kidney, skeletal muscle, brain, blood cells, and lungs. LDH is very important for metabolism.
LDH exists in 5 forms (isoenzymes), which differ slightly in structure. LDH-1 is found primarily in heart muscle and red blood cells. LDH-2 is concentrated 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.
What abnormal results mean
Because LDH can be found in many tissues in the body, total LDH is not specific for heart disease. Normally, the concentration of LDH-2 is greater than LDH-1. However, after a heart attack, the concentration of LDH-1 is generally higher than that of LDH-2. (This is called a “flipped” LDH pattern.) The LDH level rises within 24 to 72 hours after a heart attack, peaks in 3 to 4 days, and returns to normal in about 14 days.
Greater-than-normal LDH isoenzyme levels may be seen in:
- Heart attack
- Hemolytic anemia
- Infectious mononucleosis
- Intestinal ischemia (blood deficiency) and infarction (tissue death)
- Liver disease (e.g., hepatitis)
- Muscle injury
- Muscular dystrophy
- Pulmonary (lung) infarction (tissue death)
- Ischemic cardiomyopathy
What the risks are
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
Drugs that can increase LDH measurements include anesthetics, aspirin, clofibrate, fluorides, mithramycin, narcotics, and procainamide.
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.
by Brenda A. Kuper, M.D.