What specific blood tests should a patient with a low Body Mass Index (BMI) and symptoms of chest pain and syncope, with a normal Electrocardiogram (ECG) pattern, undergo to confirm a diagnosis?

Blood Tests for Patient with Low BMI, Chest Pain, Syncope, and Normal ECG

For a patient with low BMI, chest pain, syncope, and normal ECG, targeted cardiac biomarker testing with troponin T or I and CK-MB is essential to rule out myocardial injury, along with CBC, electrolytes, BUN/creatinine, and blood glucose to evaluate for other potential causes.

Cardiac Biomarker Testing

Primary Cardiac Tests

• Troponin T or I: Most specific marker for cardiac cell damage 1

  • Should be measured on admission and at 10-12 hours after symptom onset 1
  • High sensitivity troponin assays can detect even minor cardiac injury
  • Normal level on initial presentation (especially within 6 hours of chest pain) does not exclude myocardial infarction 1

• CK-MB mass:

  • Complements troponin testing for timing of potential cardiac injury 1
  • When combined with troponin I, provides 100% negative predictive value for AMI within 12 hours 2

Additional Essential Blood Tests

Metabolic and Hematologic Assessment

• Complete Blood Count (CBC):

  • Essential to detect anemia which could explain syncope, especially in a patient with low BMI 1, 3
  • Also evaluates for infection which could contribute to symptoms

• Electrolytes, BUN/Creatinine:

  • Critical for detecting electrolyte abnormalities that may cause syncope 3
  • Particularly important in patients with low BMI who may be dehydrated or have nutritional deficiencies

• Blood Glucose:

  • Hypoglycemia can cause syncope and should be ruled out, especially in patients with low BMI 3

Targeted Testing Based on Clinical Suspicion

If Cardiac Etiology is Suspected

• Brain Natriuretic Peptide (BNP):
  • Consider if heart failure is suspected 3
  • Elevated levels of CK-MB and troponin I have been associated with congestive heart failure severity 4

If Pulmonary Embolism is Suspected

• D-dimer:
  • Consider if patient has risk factors for pulmonary embolism
  • Particularly important in patients with unexplained chest pain and syncope with normal ECG 1

Testing Strategy

1. Initial Testing: Draw troponin I/T, CK-MB, CBC, electrolytes, BUN/creatinine, and glucose immediately
2. Serial Testing: Repeat cardiac biomarkers at 6-12 hours after symptom onset 1
3. Interpretation:
   • Negative troponin and CK-MB at 12 hours effectively rules out AMI 2
   • Positive cardiac markers require immediate cardiology consultation

Important Considerations

• Avoid Routine Comprehensive Testing: The American College of Cardiology recommends targeted testing based on clinical assessment rather than indiscriminate laboratory panels 3
• Low BMI Context: Patients with low BMI may have nutritional deficiencies or eating disorders that could contribute to syncope and chest pain
• Normal ECG Does Not Rule Out Cardiac Causes: A careful laboratory evaluation is still necessary despite normal ECG findings 1

Common Pitfalls to Avoid

• Relying on a single troponin measurement: Serial measurements are essential as initial values may be normal even in cardiac injury 1
• Overlooking non-cardiac causes: While cardiac causes must be ruled out, consider metabolic, pulmonary, and hematologic causes in patients with low BMI
• Discharging too early: Observation for 10-12 hours with serial cardiac biomarker testing provides the highest diagnostic accuracy 1