Cardiac Enzymes

Certain enzymes (CPK, LDH, SGOT) are released from the heart muscle cells when it is injured (“heart attack”). These enzymes are normally found in the blood at low levels.

• The abnormal elevation of these enzymes in the blood stream can occasionally be the only indicator that a heart attack (myocardial infarction) has occurred.
• The physician will test the cardiac enzymes in situations where a myocardial infarction is suspected (patient with chest pain).
• A venipuncture specimen is needed to perform this special test.

Patients known to have had a heart attack may have cardiac enzymes monitored over several days to document improvement. Often the cardiac enzymes will not be abnormally elevated until 24 hours after the onset of the chest pain.

One of the most reliable and commonly tested cardiac enzymes is creatinine phosphokinase (CPK). CPK is present in all muscle tissue (skeletal, cardiac, and smooth muscle), but the CPK-MB fraction is released specifically from injured heart muscle.

Normal Levels:
TOTAL CPK 30-150 IU/dl
CPK-MB 0-5 IU/dl

An abnormal elevation in the total CPK and the CPK-MB is diagnostic for a heart attack, even in cases where the ECG may be normal. Increased diagnostic accuracy is found when this blood test is performed serially (over 24 hours) with the ECG. The CPK-MB enzyme is not expected to rise until 12-24 hours aftera heart attack has occurred. This fact makes the immediate diagnosis (or exclusion) of myocardial infarction impossible in cases where the ECG is normal.