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Does Elevated Cardiac Biomarker Indicate Heart Disease Risk? When a person complains of chest pain, shortness of breath and other heart attack symptoms, or this person has abnormal electrocardiography (ECG) results, the doctor will usually order a test to confirm whether this patient has suffered a heart attack (also known as myocardial infarct). The purpose of the test is to measure the patient’s biomarkers in the blood. These biomarkers include enzymes, hormones, and proteins. Cardiac enzymes are proteins produced by the body to speed up specific biochemical reactions within heart cells. When heart muscle is damaged by say a heart attack or other conditions, a number of proteins including cardiac enzymes are released into the bloodstream. These enzymes include Creatine kinase (CK) and a subtype of this enzyme called CK-MB. CK is found in the heart, skeletal muscle and brain, but CK-MB is found almost exclusively in the heart. For many years, enzyme test measuring CK and CK-MB had been used to diagnose heart attacks. Recently, these tests have been replaced by measuring another protein called troponin. It a complex of regulatory proteins, which includes troponin T (TnT) and troponin I (TnI) that help control how the heart muscles contract. Troponin is a reliable indicator that heart cell damage has occurred. Because troponin is not an enzyme, most doctors now refer to biomarker tests instead of enzyme tests.
Troponin is by far the most commonly used
biomarker as it has the highest known sensitivity. It enters into the
bloodstream soon after a heart attack, and it will stay in the bloodstream days
after all other biomarkers go back to normal levels. Current guidelines from the
American Heart Association (AHA) indicate that this is the best biomarker for
finding a heart attack.
Sometimes, doctor may want to measure myoglobin that is a small protein that stores oxygen in addition to troponin to help diagnose a heart attack. But It is not very specific for finding a heart attack. Biomarker testing can also be used to check for injury to the heart after some forms of cardiac surgery. During the recovery period following a heart attack or injury, such tests can help determine if a cardiac procedure or a medicine being used to dissolve a blockage (thrombolytic medicine) has successfully restored blood flow through a blocked coronary artery. But results of these tests are not always completely clear-cut. As cardiac enzymes and proteins leak slowly into the bloodstream, it may take up to 6 hours for high levels to appear in the bloodstream after the onset of a heart attack. So, a person who is experiencing chest pain with normal cardiac biomarkers does not mean that he or she is not having a heart attack. In these cases, cardiac biomarker tests are normally repeated to confirm the diagnosis of a heart attack. Nevertheless, not all elevation in cardiac biomarkers point to a heart attack. For instance, some cardiac enzymes like CK and CK-MB, which are also found in other body tissues, may rise when these other tissues are damaged. While elevation in the troponin blood level is really quite specific for cardiac cell damage, there should be no such thing as false elevation of troponin. But other than heart attack, some conditions like heart failure, myocarditis, rapid atrial fibrillation, sepsis, coronary artery spasm, aortic dissection, stress cardiomyopathy, or severe pulmonary embolism (blockage of an artery in the lungs) can also damage heart cells. Meanwhile, other factors like pulmonary hypertension, kidney disease or even prolonged exercise may cause cardiac biomarkers to rise, too.
Hence, diagnosis of a heart attack should not rely
on a single blood test. Doctors should also look at clinical symptoms, physical
examination findings, electrocardiogram (EKG, ECG) results, and often on a
pattern of biomarker elevations suggesting acute heart cell injury. Date: February 28, 2019
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