Cardiac Troponin I Project: use of cardiac Troponin I as early marker of acute myocardial infarction versus CK-MB and CK-MB isoforms

• Aim of Project:
  To determine whether the measurement of cardiac Troponin I, in conjunction with Myoglobin, has sufficient sensitivity and specificity in detecting acute myocardial infarction (AMI) compared to the measurement of Creatine Kinase- MB (CK- MB) and CK-MB isoforms.
  
  CK-MB isoforms and myoglobin are the earliest markers for diagnosis of AMI (within 6 hours of the onset of chest pain). CK-MB isoforms are fairly specific for cardiac injury. However, their measurement requires a dedicated high-voltage electrophoresis analyzer with batch-mode operation. Myoglobin is not specific for cardiac injury since it is also increased in patients with skeletal muscle injury or renal failure. CK-MB has long been considered the test of choice for diagnosis of AMI due to its high specificity for cardiac injury and the relative ease of testing. Cardiac Troponin I (cTnI) has the potential to replace CK-MB in this role. cTnI is absolutely cardiospecific and is also elevated after AMI for up to 5-7 days.
  
  Our study assesses the performance of cTnI, used in conjunction with Myoglobin, in detecting AMI. cTnI and Myoglobin can be performed rapidly on random access analyzers. If the combination of these two tests can be shown to be a sensitive and specific panel for acute cardiac injury, this will represent the most cost-effective tool for diagnosis of AMI yielding the most optimal patient management.
  
  
• Materials and Methods:
  We used the Access, a random-access analyzer by Beckman, to perform cTnI, Myoglobin, and CK-MB. The analyzer was located in our laboratory at Lyndon B. Johnson (LBJ) Hospital. Patient testing (cTnI, Myoglobin, and CK-MB) was performed on each sample from two patient populations:
  - 30 samples from Ben Taub laboratory. These were aliquots from samples obtained for patients seen in the Emergency Center (EC) with chest pain who required CK-MB isoforms testing to rule out AMI. These samples were sent to Methodist Laboratory for CK-MB isoforms testing, of which the results were available to Ben Taub Hospital.
  
  - 50 samples from Lyndon B. Johnson laboratory. These were aliquots from samples obtained for any patient at LBJ who required CK-MB for diagnosis of AMI. This patient population included inpatients, clinic patients and EC patients at LBJ.
  
  CK-MB was performed on the Stratus Immunoassay analyzers at both hospitals. CK-MB isoforms were performed at Methodist Hospital on the Cardio REP analyzers (Helena, electrophoresis methodology).
  
  
• Results:
  Cardiac Troponin I was found to be as sensitive as CK-MB isoforms in early detection of acute MI. However, cardiac Troponin I is elevated up to 2 weeks after acute MI. Myoglobin was found to be the most sensitive but was also the least specific. The best role for cardiac Troponin I and myoglobin would be complementary tests for CK-MB in early MI detection
  
  
• Publication:
  Pending (manuscript in progress)

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