When you suffer a heart attack, medically termed a myocardial infarction, damage occurs to certain parts of your heart muscle, weakening its ability to pump. Damaged muscle allows enzymes to leak from the muscle into your bloodstream. Testing your blood for certain enzymes, also called cardiac markers, after a heart attack can help with diagnosis and management.
Types
The main cardiac enzymes tested after a suspected heart attack include creatine phosphokinase, or CPK, also called creatine kinase, or CK. Your doctor may also test for a fraction of CPK called CPK-MB. Other proteins released from damaged muscle include troponin T and troponin I. Less frequently used tests include aspartate aminotransferase, or AST and aspartate aminotransferase, also called AST or SGOT, which are also elevated if you have liver damage and lactate dehydrogenase, or LDH.
Uses
Troponins T and I have become the most commonly used cardiac markers for heart muscle damage, according to the General Practice Notebook, because they are proteins specific to heart muscle. These two measurements along with CK also rise the soonest after a heart attack, normally within 4 to 6 hours, but CK is not as specific for heart muscle damage. High levels of CK are also found in skeletal muscle and the brain. Lactase Dehydrogenase is found in liver, kidney, skeletal muscle, brain, blood cells, and lungs as well as in heart muscle, making a rise non-specific for heart disease.
Significance
Your blood normally has very low levels of troponins, generally less than 0.2 micrograms per liter for TnT and less than 0.3 mcg/L for TnI. A rise in TnI or TnT indicates damage to the heart muscle, but could indicate another type of heart disease besides heart attack, such as heart failure, pericarditis, severe hypertension or pulmonary embolism. Troponin normally remains in the bloodstream longer than other enzymes, such as CPK-MB, as long as 10 to 14 days, according to the American Heart Association. Changes in CK-MB levels can also help your doctor assess whether thrombolytic drugs are helping to dissolve a blood clot in the coronary artery that is decreasing the blood supply to the heart. A continued rise in the CK-MB levels three days after a heart attack can indicate an increase in heart muscle damage.
Caveats
Because diseases other than heart attack can cause a rise in cardiac markers, blood tests are used in conjunction with other heart tests such as electrocardiograph as well as clinical symptoms to make a diagnosis. Taking a series of blood tests and comparing results can best help your doctor assess any damage to your heart.
References
- American Heart Association: Blood Tests for Rapid Detection of Heart Attack
- Georgia Health Sciences University: Diagnostic Tests for Myocardial Infarction
- HealthWise; Cardiac Enzyme Studies; August 2009
- Leeds Teaching Hospitals: Troponin & Cardiac Enzymes
- MedlinePlus; Lactate Dehydrogenase Test; March 2010
- GP Notebook: Cardiac Enzymes
