Cardiac Testing

Cardiac testing in the lab generally involves monitoring of cardiac markers, which are elevated when damage occurs to the heart. These markers include:

• C-reactive protein (CRP)
• Creatine kinase (CK)
• Myoglobin
• NT-proBNP
• Troponins

Overview

• Myoglobin is earliest marker (but declines quickly)
• Cardiac troponin 1 is most cardiac-specific
  • High-sensitivity cTnI used for investigating heart attacks
  • Detectable quickly (3-12 hours), and remain elevated >1 week
• CK-MB/CK2 occurs later and lasts longer (CK isoenzyme associated with cardiac and skeletal muscle)

Others

• CRP is acute inflammatory marker, can also be used to assess future risk for CVD
• NT-proBNP elevated in heart failure

C-reactive protein

C-reactive protein is an non-specific, acute phase reactant that is produced as a part of inflammatory processes. The assay can be used to investigate a variety of disorders that are associated with inflammation, including infections, autoimmune conditions, necrosis, etc.

• CRP is generally a better indicator of inflammatory processes than the ESR.

C-reactive protein	RI: <10 mg/L
	▲ Increased	▼ Decreased
Conditions	Bacterial infections Surgical complications (e.g., infection, clots) Autoimmune diseases (arthritis, Crohn's disease, etc.) Vascular diseases Including increased risk of cardiovascular ischemia Tissue damage Acute myocardial infarction Malignancy
Lab Interferences
Other Factors	Smoking Hypertension Low HDL/high triglycerides Elevated BMI Diabetes Chronic infections (e.g., gingivitis) Medications	Medications, especially anti-inflammatory drugs Exercise, weight loss Alcohol consumption

High-sensitivity C-reactive protein

This CRP assay has an increased sensitivity, allowing for the monitoring of low-level inflammation that may indicate future cardiac events.

• Athermomatous plaques in arteries release inflammatory molecules, making baseline hs-CRP values useful in monitoring risk of future cardiac events in patients with stable or acute coronary diseases.
  • Low risk: 0.7 - 1.1 mg/L
  • Moderate risk: 1.2 - 1.9 mg/L
  • High risk: 2.0 - 3.8 mg/L
• Can be used alongside lipid testing for cardiac risk scores (e.g., Framingham risk score)

Creatine kinase

This non-specific enzyme is has 3 isoenzymes that are found within various tissues, including the heart, skeletal muscle, and brain.

• CK-MM (96-100%)
• CK-MB (CK2) (0-6%)
• CK-BB (0%)

CK-MB is the enzyme that is most specific for heart muscle damage.

• Levels rise 3-6 hours after damage
• After damage stops, peaks 12-24 hours after
• Returns to normal 12-48 hours after peak (4-5 days total)

Creatine Kinase	Adult Male: 20 - 215 IU/L Adult Female: 20 - 160 IU/L Newborn: 68 - 580 IU/L
	▲ Increased
Conditions	Acute myocardial infarction Cardiac surgeries Cardiac defibrillation Myocarditis Ventricular arrhythmias Cardiac ischemia
Lab Interferences
Other Factors	Damage to skeletal muscle can also increase CK Intramuscular injections can increase CK levels