Cardiac Panel
TECHNICAL UPDATE

DESCRIPTION/BACKGROUND INFORMATION:

According to the World Health Organization and further updated by the European Society of Cardiology and the American College of Cardiology criteria for diagnosis of acute myocardial infarction (AMI) was the presence of any two of the following: 1) Patient history and physical for symptoms of ischemia; 2) ECG changes consistent with ischemia; and/or 3) Changes in serum protein markers associated with MI.

Blood protein markers play an important role in the differential diagnosis of AMI when other indicators may be negative or questionable. Markers used in the diagnosis of MI include: Creatinine Kinase (CK), the MB isoenzyme of creatinine kinase (CK-MB), myoglobin, and Troponin I.

CLINICAL APPLICATION:

CK - Creatinine kinase is an enzyme found in the heart, brain, and skeletal muscle. CK occurs in three major forms, called isoenzymes:

• CK-MB (found mostly in your heart muscle),
• CK-BB (found mostly in your brain), and
• CK-MM (found in your heart and other muscles).

CK in the blood comes mainly from your muscles. The CK in your brain almost never gets into the blood.

Myoglobin - Myoglobin is always detectable in serum, but in heart muscle injury, such as AMI, a rise in myoglobin can be detected in the blood as early as one to two hours after the onset of the AMI, reaching a peak between 6 and 8 hours after the onset of symptoms. Myoglobin is best assessed by measuring myoglobin twice, once at presentation and then two hours later. Two consecutive equal (and preferably low) myoglobin levels would indicate that no AMI occurred. Therefore the absence of a rise can be used to effectively rule-out a heart attack - myoglobin has a high negative predictive value and is particularly useful when the clinical history of the patient is known. Blood myoglobin concentrations may be elevated as a result of a variety of conditions that produce muscle damage. These include trauma, ischemia, surgery, exercise and a variety of degenerative muscular diseases.

CK-MB and CK-MB Index - Blood concentrations of CK-MB can be elevated as a result of acute or chronic muscle damage, including strenuous exercise and trauma. Typically, CK-MB increases above normal within the first 4-8 hours following an AMI, reaching maximum concentrations between 12 and 24 hours. CK-MB should be evaluated in context to the total CK (relative index). If the relative index is more than 5, the heart is the likely muscle damaged. A high CK with a very low relative index suggests that other muscles were damaged. Blood concentrations of CK-MB can be elevated as a result of acute or chronic muscle damage, including strenuous exercise and trauma.

Troponin I - Cardiac troponin I is primarily elevated as a result of MI. Troponin I concentrations become elevated between 4 and 8 hours following an AMI. The concentrations peak between 12 and 16 hours and remains elevated for 5-9 days following damage to the myocardium. Cardiac troponin I may be elevated in the absence of an elevated myoglobin or CK-MB and due to the increased analytical specificity and the increased duration of the elevation, cardiac troponin I has become an important marker in the diagnosis and evaluation of patients suspected of having an MI. Cardiac troponin I may be elevated as a result of minor cardiac injury that includes: unstable angina, cardiac contusions, cardiac transplant, coronary artery bypass graft surgery, physical trauma to the heart, congestive heart failure and other conditions that may damage the myocardium.

Simultaneous quantification of myoglobin, CK-MB, and cardiac troponin I following AMI can greatly assist the physician in the management of patients suspected of presenting with an AMI.

TEST NAME & NUMBER:

• 2610 Cardiac Panel

REFERENCES:

1. Alan H.B. Wu; Fred S. Apple; W. Brian Gibler; Robert L. Jesse; Myron M. Warshaw; Roland Valdes Jr. National Academy of Clinical Biochemistry Standards of Laboratory Practice: Recommendations for the Use of Cardiac Markers in Coronary Artery Diseases. Clinical Chemistry 45:7 1104-1121 (1999).
2. Peter A. Kavask PhD; Viliam Lustig, PhD FCACB; Rakesh Bhargava, M.D. FRCPC; Andrew R. MacRae, PhD, FCACB. When is a Heart Attack a Heart Attack? Advance/Laboratory (Jan 2004).
3. Triage Cardiac Panel, package insert. Biosite (Jan 27, 2003).