Serum Enzymes and Cardiac Markers 

Normal adults serum enzymes /cardiac markers 

Creatine kinase (CK)  -------> 26 - 174 units/L

Creatine kinase isoenzymes

• CK-MB -------> 0%  - 5% of total
• CK-MM-------> 95%  - 100% of total 
• CK-BB---------> 0%

Lactate dehydrogenase ----> 140 - 280 units/L

Lactate dehydrogenase isoenzymes

• LDH1--------> 14% - 26%
• LDH2--------> 29% - 39%
• LDH3--------> 20% - 26%
• LDH4-------->  8% - 16%
• LDH5-------->  6% - 16%

Troponin I = <0.6 ng/mL; >1.5 ng/mL indicates myocardial infarction 

Troponin T = >0.1 - 0.2 ng/mL indicates myocardial infarction 

Myoglobin = <90 mcg/L elevation could indicate myocardial infarction 

Description 

• Creatine kinase is an enzyme found in muscle and brain tissue that reflects tissues catabolism resulting from cell trauma. 
• The CK level begins to rise within 6 hours of muscle damage,  peaks at 18 hours, and returns to normal in 2 to 3 days.
• The test for CK is performed to detect myocardial or skeletal muscle damage or central nervous system damage,  normal CK value is 26 to 174 units/L
• Isoenzymes include CK-MB (cardiac),  CK-BB (brain) and CK-MM (muscle)
• Isoenzyme CK-MB is found mainly in cardiac muscle, CK-BB is found mainly in brain tissue, and CK-MM is found mainly is skeletal muscle. 

Values 

• CK-MB: 0% to 5% of total
• CK-MM: 95% to 100% of total 
• CK-BB: 0%

Nursing considerations 

• If the test is to evaluate skeletal muscle instruct the client to avoid strenuous physical activity for 24 hours before the test.
• Also instruct the client to avoid ingestion of alcohol for 24 hours before the test.
• Invasive procedures and intramuscular injections may falsely elevate CK level.

Lactate dehydrogenase (LDH)

Description 

• The LDH isoenzymes affected by acute myocardial infraction are LDH 1 and LDH 2
• The LDH level begins to rise about 24 hours after myocardial infraction and peaks in 48 to 72 hours; thereafter, it returns to normal, usually within 7 to 14 days.
• The presence of an LDH flip ( when LDH1 is higher than LDH2) is helpful in diagnosing a myocardial infarction. 

Nursing considerations 

• The LDH isoenzyme levels should be interpreted in view of the clinical findings. 
• Testing should be repeated on 3 constructive days.

Troponins

Description 

• Troponin is a regulatory protein found in striated muscle ( skeletal and myocardial ).
• Increased amounts of troponins are released into the bloodstream when an infraction causing damage to the myocardium.
• Levels elevate as early as 3 hours after myocardial injury. Troponin 1 levels may remain elevated for 7 to 10 days and troponin T levels may remain elevated for up to 10 to 14 days.
• Serial measurements are important to compare with a baseline test.

Values

• Troponin 1: value usually is lower than 0.6 ng/mL; higher than 1.5 ng/mL is consistent with a myocardial infarction. 
• Troponin T: Higher than 0.1 to 0.2 ngm/L is consistent with a myocardial infarction. 

Nursing considerations 

• Testing is repeated in 12 hours, followed by daily testing for 3 to 5 days.
• Rotate venipuncture sites.

Myoglobin 

Description 

• It is an oxygen-binding protein found in striated ( cardiac and skeletal ) muscle that releases oxygen to very low tensions. 
• Any injury to skeletal muscle will cause a release of myoglobin into the blood.

Values: Normal value is lower than 90 mcg/L an elevation could indicate myocardial infarction. 

Nursing considerations 

• The level can rise as early as 2 hours after a myocardial infarction, with a rapid decline in the level after 7 hours.
• Because the myoglobin level is not cardiac-specific and rises and falls so rapidly, its use in diagnosing myocardial infraction may be limited.