Laboratory Testing for Syncope Evaluation
Targeted blood tests based on clinical assessment are reasonable in syncope evaluation, while routine comprehensive laboratory testing is not recommended. 1
Approach to Laboratory Testing in Syncope
Recommended Laboratory Tests
- Targeted testing based on history, physical examination, and ECG findings:
- Complete blood count (CBC): When suspecting anemia or infection
- Electrolyte panel: When suspecting electrolyte abnormalities
- Blood glucose: When suspecting hypoglycemia
- Cardiac biomarkers: Consider in selected cases with suspected cardiac etiology
Cardiac Biomarkers
- Brain natriuretic peptide (BNP): May be considered when cardiac cause is suspected
- High-sensitivity troponin: Limited value unless acute myocardial infarction is suspected
- Has modest predictive value for major adverse cardiovascular events
- Threshold of >50 ng/L may be significant for cardiac evaluation 2
When to Order Laboratory Tests
Clinical Scenarios Warranting Testing
- Suspected blood loss: CBC for patients with history of peptic ulcer disease or tarry stools
- Suspected dehydration: Electrolytes, BUN/creatinine
- Suspected cardiac etiology: Consider troponin and BNP, especially in:
Testing Based on Patient Demographics
- Older adults: More likely to need cardiac biomarkers as they have higher likelihood of cardiac causes 3, 4
- Younger adults: Less likely to need extensive laboratory testing as vasovagal syncope is more common 3
Limitations and Caveats
- Low diagnostic yield: Routine laboratory testing has low diagnostic yield when used indiscriminately 1
- No proven outcome benefit: Laboratory testing results have not been linked to improved clinical decision-making or outcomes 1
- Avoid broad-panel testing: Class III recommendation (No Benefit) for routine comprehensive laboratory testing 1
- Serial troponin testing: Initial troponin has clinical value, but serial testing may have limited utility in patients presenting with ground-level falls and possible syncope 2
Common Pitfalls to Avoid
- Ordering comprehensive laboratory panels without specific indications
- Failing to tailor testing to clinical presentation
- Overreliance on laboratory tests rather than thorough history and physical examination
- Assuming normal laboratory values rule out serious causes of syncope
Remember that laboratory testing should be part of a targeted diagnostic approach based on the initial evaluation and risk stratification, not a reflexive battery of tests for all syncope patients.