Laboratory Workup for Intermittent Palpitations
Order thyroid-stimulating hormone (TSH), complete blood count (CBC), and serum electrolytes (including calcium and magnesium) as your initial laboratory panel for this patient with intermittent palpitations. 1, 2
Essential Initial Laboratory Tests
The following targeted laboratory tests should be ordered based on the clinical presentation of palpitations without current ECG documentation:
- Thyroid-stimulating hormone (TSH) to rule out hyperthyroidism, which is a common non-cardiac cause that must be excluded 1, 2
- Complete blood count (CBC) to assess for anemia, which can precipitate palpitations 2
- Serum electrolytes including calcium and magnesium to identify electrolyte disturbances that can trigger arrhythmias 1, 2
- Fasting blood glucose or glycohemoglobin to identify hypoglycemia or diabetes 2
Additional Tests Based on Clinical Context
If there is suspicion of structural heart disease or renal dysfunction, consider:
- Blood urea nitrogen (BUN) and serum creatinine to evaluate renal function, particularly important for medication decisions 2
- 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 2
Critical Pitfall to Avoid
Do not order routine comprehensive laboratory panels. 2 The American College of Cardiology explicitly states that routine and comprehensive laboratory testing is not useful in the evaluation of patients with palpitations. 2 Instead, targeted blood tests should be ordered based on specific clinical suspicion from the history, physical examination, and ECG findings. 2
Rationale for This Approach
Laboratory testing is most valuable when loss of circulating volume is suspected (dehydration, bleeding) or metabolic causes are suggested by history (thyroid symptoms, medication use, substance use). 2 Since this patient has been previously told her symptoms are due to anxiety but suspects an alternative cause, the focused laboratory workup above will efficiently screen for the most common metabolic and endocrine causes of palpitations without unnecessary testing.
Next Steps Beyond Laboratory Work
Since the 24-hour Holter monitor was unremarkable but the patient did not experience symptoms during monitoring, extended cardiac monitoring with an event recorder or implantable loop recorder is more appropriate than repeat Holter monitoring. 1, 2 Event recorders have superior diagnostic yield and are more cost-effective for symptoms occurring several times per week, while implantable loop recorders should be considered for symptoms less than twice monthly with severe features. 1, 3