What is the laboratory workup for syncope (fainting)?

From the Guidelines

The lab workup for syncope should be tailored to the patient's history and physical examination, and may include a complete blood count (CBC), basic metabolic panel (BMP), cardiac enzymes (troponin), and electrocardiogram (ECG) as indicated by the clinical presentation. According to the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1, the initial evaluation should include a thorough history, physical examination, and ECG. Additional testing such as orthostatic vital signs, echocardiogram, and prolonged cardiac monitoring may be appropriate based on the patient's symptoms and risk factors.

Key Considerations

• The workup should focus on identifying life-threatening conditions such as cardiac ischemia, arrhythmias, and structural heart disease.
• The diagnostic yield is highest when tests are selected based on specific clinical suspicions rather than performed as a standard battery.
• Not all patients require extensive testing, and the goal is to avoid unnecessary testing in patients with benign causes of syncope.
• The evaluation should also consider non-cardiac causes of syncope, such as vasovagal reactions, orthostatic hypotension, and neurological disorders.

Additional Testing

• Thyroid function tests, toxicology screening, and pregnancy tests (for women of childbearing age) may be appropriate in selected cases.
• Brain natriuretic peptide (BNP) can help identify heart failure as a potential cause of syncope.
• Imaging of the brain with either CT or MRI may be indicated if a neurological basis of syncope is suspected, as recommended by the AHA/ACCF scientific statement on the evaluation of syncope 1.

Clinical Judgment

• The choice of tests should be guided by the patient's clinical presentation, medical history, and physical examination findings.
• The 2004 European Heart Journal guidelines on management of syncope also emphasize the importance of a thorough initial evaluation, including history, physical examination, and ECG, to determine the cause of syncope and guide further testing 1.

From the Research

Initial Assessment

The initial assessment for patients presenting with syncope includes:

• A detailed history 2, 3, 4, 5, 6
• Physical examination 2, 3, 4, 5, 6
• Electrocardiography (ECG) 2, 5, 6
• Orthostatic assessment 3, 5

Laboratory Testing and Neuroimaging

• Laboratory testing and neuroimaging have a low diagnostic yield and should be ordered only if clinically indicated 2
• Examples of diagnostic tests that may be used in the evaluation of syncope include:
  • 12-lead electrocardiogram 6
  • Holter monitoring 6
  • Echocardiogram 6
  • Tilt table testing 5, 6
  • Ischemia evaluation 6
  • Electrophysiologic studies 6
  • Other imaging tests 6

Risk Stratification

• The initial evaluation may diagnose up to 50% of patients and allows immediate short-term risk stratification 2
• Several comparable clinical decision rules can be used to assess the short-term risk of death and the need for hospital admission 2
• Low-risk patients with a single episode of syncope can often be reassured with no further investigation 2
• High-risk patients with cardiovascular or structural heart disease, history concerning for arrhythmia, abnormal electrocardiographic findings, or severe comorbidities should be admitted to the hospital for further evaluation 2