From the Guidelines
For syncope evaluation, initial laboratory tests should be tailored to the patient's history, physical examination findings, and suspected underlying causes, and may include a complete blood count (CBC), basic metabolic panel (BMP), cardiac enzymes (troponin), and electrocardiogram (ECG) if syncope may be due to loss of circulating volume, or if a syncope-like disorder with a metabolic cause is suspected, as recommended by the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1. The CBC helps identify anemia which can cause reduced cerebral perfusion. The BMP assesses electrolyte abnormalities, particularly potassium, sodium, calcium, and magnesium imbalances that can trigger arrhythmias. Blood glucose measurement is crucial to rule out hypoglycemia as a cause. Cardiac enzymes help identify if myocardial damage occurred. Additional tests may include thyroid function tests if thyroid disease is suspected, toxicology screening if drug-induced syncope is possible, and pregnancy test for women of childbearing age. Brain natriuretic peptide (BNP) may be ordered if heart failure is suspected. These tests help identify metabolic, cardiac, or other systemic causes of syncope, though many cases remain idiopathic even after thorough evaluation. The specific combination of tests should be tailored to the patient's history, physical examination findings, and suspected underlying causes rather than ordering all tests for every patient, as supported by the guidelines from the European Heart Journal 1. It is also important to note that routine cardiac imaging is not useful in the evaluation of patients with syncope unless cardiac etiology is suspected on the basis of an initial evaluation, including history, physical examination, or ECG, as stated in the 2017 ACC/AHA/HRS guideline 1. Tilt-table testing may be useful in selected patients presenting with syncope if the diagnosis is unclear after initial evaluation, as recommended by the 2017 ACC/AHA/HRS guideline 1. Overall, the evaluation of syncope should be guided by the patient's clinical presentation and suspected underlying causes, and should include a combination of laboratory tests and other diagnostic evaluations as needed.
From the Research
Laboratory Tests for Syncope
The following laboratory tests may be ordered for patients with syncope:
- Hemoglobin measurement if gastrointestinal bleeding is suspected 2
- Cardiac biomarkers as a component of risk stratification tools, such as the Canadian Syncope Risk Score 2
Diagnostic Tests
Other diagnostic tests that may be ordered include:
- Electrocardiogram (ECG) as the only instrumental test recommended for the initial evaluation of syncope 3, 4
- Echocardiography, Holter monitoring, or exercise testing for patients with syncope and heart disease 4
- Tilt test and carotid sinus massage to reproduce reflex syncope 4
- Insertable subcutaneous loop recorder for prolonged ECG monitoring 4
- Neuroimaging if findings suggest a neurologic event or a head injury is suspected 2
Evaluation Approach
The evaluation of syncope should include:
- A thorough clinical history and physical examination, including orthostatic assessment 2, 5, 6
- Short-term risk assessment to determine the need for admission 5
- Monitoring for patients with suspected cardiac syncope until a diagnosis is made 5
- Outpatient evaluation with tilt-table testing for patients with suspected reflex syncope or orthostatic hypotension 5