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

Laboratory Testing for Female Patient with Palpitations

Order thyroid-stimulating hormone (TSH), complete blood count (CBC), and serum electrolytes (including potassium, calcium, and magnesium) as your initial laboratory workup for palpitations. 1, 2

Essential Initial Laboratory Tests

The targeted laboratory approach should include:

• Thyroid-Stimulating Hormone (TSH): Hyperthyroidism is a common non-cardiac cause that must be excluded, as it occurs in 5-15% of patients with palpitations and can cause atrial fibrillation, particularly in those over 60 years. 1, 2 Restoration of euthyroid state usually results in spontaneous resolution of arrhythmias. 1

• Complete Blood Count (CBC): Anemia can precipitate compensatory sinus tachycardia and palpitations. 2

• Serum Electrolytes: Specifically potassium, calcium, and magnesium, as electrolyte disturbances can trigger arrhythmias. 3, 2 These are particularly important if the patient has risk factors for electrolyte abnormalities.

• Fasting Blood Glucose or Glycohemoglobin: To identify hypoglycemia or diabetes as potential triggers. 2

Additional Tests Based on Clinical Context

Do NOT order comprehensive laboratory panels routinely—this approach has been shown to be not useful and represents a common pitfall. 1, 2 Instead, order additional tests only when specific clinical suspicion exists:

• Renal function (BUN, creatinine): If considering antiarrhythmic medications or if hypertension is present. 1, 2

• Lyme titer: Only if bradycardia is documented and there is epidemiologic exposure. 3

• pH assessment: Only if metabolic acidosis is suspected clinically. 3

• Brain natriuretic peptide (BNP) and high-sensitivity troponin: May be considered if cardiac structural disease is suspected, though their usefulness remains uncertain in palpitation evaluation. 2

Critical Diagnostic Steps Beyond Laboratory Testing

While obtaining labs, simultaneously:

1. Obtain a 12-lead ECG immediately to look for pre-excitation (Wolff-Parkinson-White syndrome), conduction abnormalities, or ongoing arrhythmia. 3, 1, 2 Pre-excitation with palpitations requires immediate electrophysiology referral due to sudden death risk. 1

2. Characterize the pattern: Ask specifically about sudden versus gradual onset/termination (sudden suggests AVNRT or AVRT), regular versus irregular rhythm, duration, frequency, and response to vagal maneuvers. 3, 1

3. Assess for red flag symptoms: Syncope, presyncope, chest pain, or dyspnea warrant urgent evaluation and possible immediate cardiology referral. 3, 1

Common Pitfalls to Avoid

• Never start Class I or III antiarrhythmic drugs empirically without documented arrhythmia due to significant proarrhythmic risk. 1

• Do not dismiss syncope occurring with palpitations—this requires immediate specialist evaluation. 1

• Do not rely on automatic ECG interpretation systems, as they are unreliable and commonly suggest incorrect diagnoses. 1

• Avoid ordering excessive laboratory tests that are unlikely to yield diagnostic information based on the clinical presentation. 2

Next Steps After Initial Laboratory Results

If TSH is abnormal (hyperthyroidism), treat urgently with beta-blockers for rate control and refer to endocrinology. 1 If labs are normal but palpitations persist, arrange ambulatory ECG monitoring: 24-48 hour Holter for daily symptoms, or event/loop recorder for less frequent episodes. 1, 2