Laboratory Testing for Palpitations
Routine comprehensive laboratory testing is not useful in the evaluation of patients with palpitations; instead, order targeted blood tests based on specific clinical suspicion from the history, physical examination, and ECG findings. 1
Essential Initial Laboratory Tests
The following targeted tests should be ordered when clinically indicated:
- Thyroid-stimulating hormone (TSH) to rule out hyperthyroidism, which is a common reversible cause of palpitations 2
- Complete blood count (CBC) to assess for anemia, which can precipitate palpitations by increasing cardiac demand 2
- Serum electrolytes including potassium, calcium, and magnesium to identify disturbances that can trigger arrhythmias 2
- Fasting blood glucose or hemoglobin A1c to identify hypoglycemia or diabetes as potential contributors 2
Additional Testing Based on Clinical Context
When specific cardiac pathology is suspected:
- Brain natriuretic peptide (BNP) and high-sensitivity troponin may be considered if a cardiac cause is suspected, though their usefulness remains uncertain in this population 1
- Renal function tests (BUN/creatinine) should be assessed if there is concern for electrolyte abnormalities or medication dosing considerations 2
Critical Diagnostic Pitfall to Avoid
Do not order comprehensive metabolic panels routinely - this approach has been shown to have no benefit and increases costs without improving diagnostic yield. 1 The key is targeting tests based on clinical suspicion rather than ordering batteries of tests reflexively.
When Laboratory Testing is Most Useful
Laboratory testing is most valuable when:
- Loss of circulating volume is suspected (dehydration, bleeding) 1
- Metabolic causes are suggested by history (thyroid symptoms, medication use, substance use) 1
- Specific clinical findings point to systemic disease (weight loss suggesting hyperthyroidism, exercise intolerance suggesting anemia) 2
The More Important Diagnostic Steps
While targeted labs have a role, the diagnostic evaluation should prioritize:
- 12-lead ECG to identify baseline abnormalities, pre-excitation, or capture the arrhythmia if present 2, 3
- 48-hour ambulatory ECG monitoring for patients with frequent or sustained palpitations 1, 2
- Event recorders or implantable loop recorders for infrequent episodes 1, 3
- Echocardiography when structural heart disease is suspected based on history, exam, or ECG findings 1, 3
The history and physical examination remain the cornerstone of evaluation, with laboratory testing serving as a targeted adjunct rather than a screening tool. 4, 5