What laboratory tests are recommended for a patient presenting with palpitations?

Laboratory Tests for Patients Presenting with Palpitations

For patients presenting with palpitations, initial laboratory testing should include complete blood count, urinalysis, serum electrolytes, blood urea nitrogen, serum creatinine, fasting blood glucose, glycohemoglobin, lipid profile, liver function tests, and thyroid-stimulating hormone. 1

Core Laboratory Tests

• Complete blood count (CBC)

  • Identifies anemia which can cause palpitations due to compensatory tachycardia
  • Detects infections that may trigger arrhythmias

• Serum electrolytes

  • Particularly potassium, magnesium, and calcium
  • Electrolyte abnormalities can directly trigger arrhythmias
  • Hypokalemia is especially important as it can cause fatal arrhythmias and increase risk of digitalis toxicity 2

• Renal function tests

  • Blood urea nitrogen (BUN)
  • Serum creatinine
  • Important for medication dosing and identifying renal causes of electrolyte disturbances 2

• Thyroid function tests

  • Thyroid-stimulating hormone (TSH) is essential
  • Hyperthyroidism is a common non-cardiac cause of palpitations
  • The American Heart Association specifically recommends routine TSH measurement in patients with heart-related symptoms 2

• Glycemic parameters

  • Fasting blood glucose
  • Glycohemoglobin (HbA1c)
  • Hypoglycemia can trigger palpitations
  • Diabetes can contribute to cardiac pathology

Additional Laboratory Tests Based on Clinical Suspicion

• Cardiac biomarkers

  • Consider troponin if there is concern for ischemia or myocardial injury
  • Natriuretic peptides (BNP or NT-proBNP) if heart failure is suspected 2
  • BNP levels can help differentiate cardiac from non-cardiac causes of symptoms

• Lipid profile

  • Important for cardiovascular risk assessment
  • Particularly relevant if coronary artery disease is suspected

• Liver function tests

  • May reveal systemic conditions affecting cardiac function
  • Important for medication metabolism considerations

Important Considerations

• Laboratory testing should always be interpreted in conjunction with a 12-lead ECG, which is a Class I recommendation for all patients with palpitations 1

• Abnormal serum potassium requires close monitoring, as both hypokalemia and hyperkalemia can complicate therapy with various cardiac medications 2

• Natriuretic peptide levels should be interpreted cautiously in women, older adults (>60 years), and obese patients, as these factors can affect baseline values 2

• Serial monitoring of electrolytes may be necessary, particularly in patients on diuretics, ACE inhibitors, ARBs, or aldosterone antagonists 2

• Development of hyponatremia or anemia may indicate disease progression and is associated with worse outcomes 2

Clinical Pearls

• Not all laboratory abnormalities require treatment - interpret in the context of the patient's symptoms and clinical presentation

• Remember that normal laboratory values do not exclude arrhythmias as the cause of palpitations

• Laboratory testing is just one component of the diagnostic approach, which should also include ECG, ambulatory monitoring, and possibly echocardiography in selected patients

• For patients with palpitations following COVID-19 infection, consider expanded testing including cardiac troponin 1

By following this systematic laboratory testing approach, clinicians can identify potential metabolic, endocrine, and cardiac causes of palpitations, guiding further diagnostic workup and management decisions.