Definition

The lactate dehydrogenase (LDH) isoenzyme test checks how much of the different types of LDH, called isoenzymes, are present in the blood.

Alternative Names

LD; LDH; Lactic (lactate) dehydrogenase isoenzymes

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

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

Drugs that can increase LDH measurements include:

• Anesthetics
• Aspirin
• Colchicine
• Clofibrate
• Cocaine
• Fluorides
• Mithramycin
• Narcotics
• Procainamide
• Statins
• Steroids (glucocorticoids such as hydrocortisone or prednisone)

Do not stop taking any medicine before talking to your provider.

How the Test will Feel

When the needle is inserted to draw blood, some people feel slight pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

LDH is an enzyme found in many body tissues such as the heart, liver, kidney, skeletal muscle, brain, blood cells, and lungs. When body tissue is damaged, LDH is released into the blood.

The LDH test helps determine the location of tissue damage.

LDH exists in five 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.

What Abnormal Results Mean

LDH levels that are higher than normal may suggest:

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

Risks

There is little risk in having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

Pincus MR, Carty RP. Clinical enzymology. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 21.