CARDIAC BIOMARKERS: Characteristics and Types

CARDIAC BIOMARKERS:

The characteristic features of cardiac markers are:

a.      Should be tissue specific and rapidly release to circulation after tissue injury.

b.      Should be sensitive enough to distinguish minor damage in tissue.

c.     There must availability of rapid, accurate and standardized analytical method for measurement.

d.      Should persist in circulation to provide late diagnosis.

e.      Should be cheap and easily available

f.        Should be absent or not detectable in patients without myocardial damage.

  TYPES OF CARDIAC BIOMARKERS: 

Enzymatic	Non enzymatic
CK (CK-MB) – marker of injury	Troponins (T, I) – Injury marker
LDH (LDH1) – marker of injury	Myoglobin – Injury marker
AST– marker of injury	BNP (NT-proBNP) – marker of CHF
Myeloperoxidase – inflammatory marker	Ischemia modified albumin – marker of ischaemia
Matrix metalloproteinase – degrades collagen and ECM.	Cytokines (TNF, IL-1, 68, 12, 18) – inflammatory markers
	Unbound FFA – markers of ischaemia
	CRP – inflammation marker
	Oxidized LDL – atherosclerotic marker, inflammatory marker
	Nourin – released by stressed monocytes and inflammatory marker

CARDIAC TROPONIN I AND T:

These are the regulatory contractile proteins. These are the complex of 3 protein subunits, troponin C (the calcium-binding component), troponin I (the inhibitory component that inhibit myosin ATPase) and troponin T (the tropomyosin binding component). Although present in muscle, unique isoforms of troponin are present in heart called cTnT and cTnI. cTnI has additional 31 amino acids as compared to skeletal muscle making it heart specific. Similarly cardiac specific cTnT has additional 11 amino acids as compared to skeletal muscle. Different forms of troponins I exists like TIC, IC binary complex, and free I. Different modified form of troponins are also available, phosphorylated, oxidized, reduced, etc. 3-6% is cytoplasmic and remaining is present in myofibrils.

Analytical Measurement

Monoclonal antibody based ELISA test to measure cTnI and cTnT are approved by FDA which do not cross react with skeletal muscle troponins. Increase in troponins above 99^th percentile should be followed up with serial samples over 6 to 12 hour period after presentation.

The Reaction Principle

cTnT (cTnI) reacts with the monoclonal cTnT (cTnI) antibody to form a complex. This complex is linked to a dye, enzyme, or chemiluminescent reagent that is linked to a second antibody to allow for quantitation of the cTnT (cTnI) present in the patient’s sample. Chemiluminesence is the most sensitive test at this time for cTnT or cTnI

•      Reference range <0.010 µg/L

•      Reference range <0.050 µg/L

Lateral flow method: 

The test principle employs mouse monoclonal anti-cTnI antibodies, dye conjugated, anti-cTnI antibodies (goat) and polyclonal anti-mouse IgG antibodies (goat) in control line. As sample migrates through the absorbent pad human TnI reacts with anti-cTnI antibodies to form a sandwich between capture and detection antibodies this binds to the test line and produces a red violet test line. Excess conjugate reacts in the control line with the anti-mouse IgG forms a second violet line which is a control line. The test cannot detect less than 0.5 ng/ml of cTnI.

Here troponin in the sample is sandwiched between gold coated antibody and enzyme linked antibody. This complex will migrate and produce colored band in test area. Control area will also produce band and serves as quality check.