Bell's Palsy Laboratory Workup
Routine laboratory testing should NOT be obtained in patients with new-onset Bell's palsy. 1
Core Recommendation
The American Academy of Otolaryngology-Head and Neck Surgery explicitly recommends against routine laboratory testing for Bell's palsy, as it is costly, rarely alters diagnosis or management, and leads to unnecessary workups of false-positive results. 1 The diagnosis is clinical, based on acute unilateral facial weakness involving the forehead without other identifiable causes. 1
When Laboratory Testing IS Indicated
Targeted testing should only be performed when specific risk factors or atypical features are identified during history and physical examination: 1
Lyme Disease Serology
- Order in endemic areas or with recent travel to endemic regions, particularly when exposure history is suggestive (outdoor activities, tick exposure). 1
- Lyme disease causes up to 25% of facial paralysis cases in endemic areas. 1
- Two-step testing approach: Initial ELISA or IFA screening, followed by Western blot confirmation if positive or borderline. 1
- ELISA is more reliable than IFA but IFA may be used if ELISA is unavailable. 1
Other Targeted Testing (Only with Specific Clinical Suspicion)
- HIV testing: Only when risk factors present or systemic symptoms suggest immunodeficiency. 2
- Diabetes screening: May be considered given higher incidence in diabetic patients, but not routinely required. 3
- Heavy metal screening: Only with occupational or toxin exposure history. 2
Red Flags Requiring Broader Workup
If ANY of these atypical features are present, the diagnosis is NOT Bell's palsy and additional testing/imaging is warranted: 1, 4
- Bilateral facial weakness (extremely rare in Bell's palsy) 4
- Isolated branch paralysis (not diffuse facial nerve involvement) 1
- Other cranial nerve involvement 1
- Second paralysis on the same side 1
- Slow progression beyond 72 hours 4
- History of head/neck cancer 4
- Symptoms suggesting central pathology (dizziness, dysphagia, diplopia) 1
Common Pitfalls to Avoid
- Ordering extensive "neuropathy panels" or viral serologies without clinical indication wastes resources and generates false positives requiring additional workup. 1, 2
- Missing Lyme disease in endemic areas by failing to ask about geographic exposure and outdoor activities. 1
- Ordering imaging routinely is not indicated for typical Bell's palsy presentation. 1
- Delaying treatment while awaiting test results reduces corticosteroid effectiveness, which must be initiated within 72 hours. 5
The Bottom Line
Bell's palsy is a clinical diagnosis requiring NO laboratory testing in typical presentations. 1 The only exception is Lyme serology in endemic areas or with exposure history. 1 Focus clinical effort on thorough history and cranial nerve examination to exclude alternative diagnoses, ensure eye protection, and initiate corticosteroids within 72 hours. 1, 5