Lactate Dehydrogenase (LDH) Isoenzymes Test

The lactate dehydrogenase (LDH) isoenzymes test is a laboratory procedure used to measure the levels of different forms of the enzyme lactate dehydrogenase in the blood or other bodily fluids. LDH is an enzyme found in many body tissues, including the heart, liver, kidney, skeletal muscle, brain, red blood cells, and lungs.

What are LDH Isoenzymes?

LDH isoenzymes are different forms of the LDH enzyme, each composed of four subunits. There are five main types of LDH isoenzymes, labeled LDH-1 to LDH-5, which vary in their composition and distribution in the body. Each type of LDH isoenzyme has a specific pattern of distribution in different tissues.

• LDH-1: Found primarily in heart muscle and red blood cells
• LDH-2: Found primarily in reticuloendothelial system
• LDH-3: Found primarily in lungs and other tissues
• LDH-4: Found primarily in skeletal muscle, kidney, and pancreas
• LDH-5: Found primarily in liver and striated muscle

Purpose of the Test

The LDH isoenzymes test is used to help diagnose and monitor a variety of conditions, including:

• Myocardial infarction (heart attack): Elevated levels of LDH-1 may indicate heart damage
• Liver disease: Elevated levels of LDH-5 may indicate liver damage or disease
• Muscle disorders: Elevated levels of LDH-4 and LDH-5 may indicate muscle damage or disease
• Cancer: Some types of cancer, such as testicular cancer, may cause elevated levels of certain LDH isoenzymes

How the Test is Performed

A blood sample is typically drawn from a vein in the arm and sent to a laboratory for analysis. The laboratory uses a technique called electrophoresis to separate the different LDH isoenzymes based on their size and charge. The levels of each LDH isoenzyme are then measured and compared to normal values.

Interpretation of Results

The results of the LDH isoenzymes test are interpreted in conjunction with other laboratory tests, medical history, and physical examination findings. Abnormal results may indicate tissue damage or disease, but must be considered in the context of the individual's overall clinical picture.