Cardiac Markers

1
Cardiac Markers

• Resident Rotation in Clinical Chemistry
• 2005-2006

2
Diagnosis of AMI

• Based on 2 out of 3 of WHO criteria
• (Circulation 90583-612, 1979)
• Prolonged chest pain
• "Silent infarct, Painless infarct
• ECG changes
• Lacks sensitivity
• ? Serum enzyme concentrations
• CKMB lacks sensitivity in diagnosis of
  perioperative MI
• Protein markers emerging in the 21st century

3
Cardiac Markers of the 21Century

• MB isoenzyme
• CKMM isoforms
• CKMB isoforms
• Myoglobin
• Troponin I
• Troponin T

4
Components in CK

• CK Isoenzymes
• CK-3 (CK-MM) in Skeletal muscle
• CK-2 (CK-MB) 10-20 in myocardiumlt2 in
  skeletal muscle
• CK-1 (CK-BB)
• Macro CKs
• Type 1Complex formed between CK-BB and
  immunoglobulin
• Type 2Mitochondria CK

5
MB Index

• MB Index (CKMB /total CK) x 100
• Rationale for using MB Index
• Using CKMB alone (RI lt4.7 ng/mL) often yields FP
  results
• Combined use with MB Index helps to rule-out
  patients with skeletal muscle injury
• What cut-off value for MB Index to use?

6
MB Index

• Sensitivity specificity
• are determined respectively at MB Index of values
  0 - 10

7
Limitations of CKMB

• FP incidents in perioperative patients without
  cardiac injury
• False elevations inFalse elevations in
• Skeletal muscle injury
• Marathon runners
• Chronic renal failure
• Hypothyroidism
• MI detection not timely enough for thrombolytic
  intervention. MB peaking takes gt12h

8
Myoglobin CKMB in typical MI

• 3 samples drawn within 2 h

9
MI Concomitant with Renal Failure

• 3 samples drawn within 2 h

10
CKMB Tpn I in AMI
11
Marker Responses to AMI
12
Troponin Release Kinetics

• Pattern of release in MI is BIPHASIC.
• Detectable in blood 4-12 h, similar to CKMB
• Peaks 12-38 h
• Remains elevated for 5-10 days

13
Receiver operating characteristic (ROC) Curve
for Tn T

• Plot of Sensitivity (TP) vs 1-specificity (FP)
• Used for establishing best discriminator for cTnT
  for predicting AMI
• Best discriminator point is 0.2 ?g/L at 9 h after
  onset of AMI