Question

A 29-year-old laborer developed chest pain while operating a pneumatic hammer on a construction project. The pain was of moderate intensity, but he felt well enough to continue work.  As the day continued, he experienced sharp pain on respiration and a tight feeling across the anterior chest wall.  He was rushed to the emergency room of a local hospital and was admitted after a brief examination.  Electrocardiographic and chest X-ray examinations were negative.  However, analysis of a blood sample revealed an elevated plasma LDH (lactate dehydrogenase) of 400IU/L (6.9mKat/L).  The high plasma LDH persisted during the next 4 days; no other laboratory or physical abnormalities appeared, and the chest pain gradually improved with bed rest. 

What other plasma enzymes might be valuable to direct the patient’s care?

Answer 1

Lactate dehydrogenase (LDH) is an enzyme required during the process of turning sugar into energy for your cells. LDH is present in many kinds of organs and tissues throughout the body, including the liver, heart, pancreas, kidneys, skeletal muscles, lymph tissue, and blood cells.

When illness or injury damages your cells, LDH may be released into the bloodstream, causing the level of LDH in your blood to rise. High levels of LDH in the blood point to acute or chronic cell damage and even some form of tissue damage. Extremely high levels of LDH could indicate severe disease or multiple organ failure.

There are five different forms of LDH that are called isoenzymes. They are distinguished by slight differences in their structure. The isoenzymes of LDH are LDH-1, LDH-2, LDH-3, LDH-4, and LDH-5.

Different LDH isoenzymes are found in different body tissues. The areas of highest concentration for each type of isoenzyme are:

• LDH-1: heart and red blood cells
• LDH-2: heart and red blood cells
• LDH-3: lymph tissue, lungs, platelets, pancreas
• LDH-4: liver and skeletal muscle
• LDH-5: liver and skeletal muscle

At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased. Thus another indicator to the patient's health may be increased levels of pyruvate in the body.