What are the advantages and disadvantages of the various biomarkers that can be used to diagnose patients with acute myocardial infarction?

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College Answer

Biomarker

Advantages

Disadvantages

TnT, TnI

Onset 2-3 hours, peak 24-36 hours,
elevated for 7-10 days
Virtually cardiac specific
Cut off 99th percentile of normal population
New assays quite sensitive
Negative test predicts low 30 day cardiac risk
Stratify short and long term risk in STEMI
Stratify short and long term risk in non
STEMI 
Detect reinfarction
AUC correlates to extent of MI

Elevated in non MI cases eg PE, myocarditis ie detects cardiac injury not cause

Assay variability (TnI) for reference range Washout and peak altered by reperfusion May need second test if first value taken too early

Modest correlation of size of MI with peak level
Some TnT present in skeletal muscle although genes different. 1st gen assays less specific (TnT)

Incomplete understanding of elevation after cardiac surgery and non cardiac surgery Baseline  higher in chronic renal failure

CK

Widely used and available

Non specific as present in skeletal muscle and brain

CK MB

Level and ratio improves specificity cf CK

Less specific and sensitive than troponin

Myoglobin

Theoretically rapid detection 

Lacks specificity and no earlier detection than Tn

AST

Historically used with CK and LDH 

Non specific

LDH

Late onset and offset 
LD1 and 2 in muscle

Present in many tissues. Requires isoenzymes

CRP

Marker of inflammation

Non specific

ESR

Additive prognostic benefit esp women

Novel biomarkers

Copeptin, if levels low can rule out MI in addition to negative Troponin

Heart-type Fatty Acid Binding Protein (H-FABP) is an early marker of ischaemia.


B-type Natriuretic Peptide (BNP) gives prognostic information post MI 

Other biomarkers of myocyte injury include  glycogen phosphorylase BB (GP-BB), myeloperoxidase, pregnancy associated plasma protein A (PAPP-A)

Raised Copeptin is not specific to cardiac disease.


Studies using H-FABP alone for diagnosis have been disappointing 

Not shown to be superior to Troponin

Discussion

The paper was written for 2010.

Since then, none of these exciting "novel biomarkers" have become commonplace.

Furthermore, the older biomarkers which are non-specific (such as AST and CK) have not fallen off the list, even though we have known since the 1950s that they are essentially useless.

In the event that the above "model" answer table is too easy to memorise, I direct the reader to a lucid interpretation of the current state by Anthony McLean et al (2012). Alternatively, this 2006 article in Circulation covers cardiovascular biomarkers in excessive pedantic detail.

References

References

McLean, Anthony S., and Stephen J. Huang. "Cardiac biomarkers in the intensive care unit." Ann Intensive Care 2.8 (2012): 1-11.