LDH isoenzymes is a test to check how much lactate dehydrogenase (LDH) is in the blood.

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 is placed around the upper arm to apply pressure and cause the vein to swell 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 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.

In 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. A bandage may be applied to the puncture site if there is any bleeding.

The health care provider may tell you to stop taking certain medicines before the test.

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is usually done when your doctor thinks you might have high LDH levels. Measurement of LDH isoenzymes helps determine the location of tissue damage.

LDH is found in many body tissues like the heart, liver, kidney, skeletal muscle, brain, blood cells, and lungs.

LDH exists in 5 forms, 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 can be measured in the blood.

Because LDH can be found in many tissues in the body, total LDH is not specific for heart disease.

Normally, the level of LDH-2 is greater than LDH-1. However, after a heart attack, LDH-1 is generally higher than LDH-2. This is called a "flipped" LDH pattern.

The LDH level rises within 24 - 72 hours after a heart attack, peaks in 3 - 4 days, and returns to normal in about 14 days.

Greater-than-normal LDH levels may suggest:

• Heart attack
• Hemolytic anemia
• Hypotension
• Infectious mononucleosis
• Intestinal ischemia (blood deficiency) and infarction (tissue death)
• Liver disease such as hepatitis
• Muscle injury
• Muscular dystrophy
• Pancreatitis
• Lung tissue death
• Stroke
• Ischemic cardiomyopathy

• 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.