What is the purpose and procedure of the tuning fork test in medical assessments?

Tuning Fork Tests for Hearing Assessment

The tuning fork test is a bedside clinical tool used to differentiate conductive hearing loss from sensorineural hearing loss through the Weber and Rinne tests, performed with a 256 or 512 Hz tuning fork. 1

Purpose

The primary purpose of tuning fork testing is to distinguish between two fundamentally different types of hearing loss that require different management approaches:

• Conductive hearing loss (CHL): Results from abnormalities in the external or middle ear that prevent sound waves from reaching the cochlea 1
• Sensorineural hearing loss (SNHL): Results from abnormalities of the cochlea, auditory nerve, or central auditory pathways 1

This distinction is clinically critical because conductive hearing loss often has treatable causes (such as cerumen impaction, middle ear fluid, or otosclerosis), while sensorineural hearing loss may require urgent intervention, particularly in sudden onset cases. 2

Proper Technique

Equipment Selection

• Use a 256 or 512 Hz tuning fork for hearing assessment 1, 3
• Strike the tuning fork on a protected elbow or knee (not on hard surfaces, which creates nonharmonic frequencies that invalidate results) 3

Weber Test Procedure

1. Place the vibrating tuning fork at the midline of the forehead or on maxillary teeth (not false teeth) 1, 3
2. Ask the patient where the sound is heard 1
3. Normal response: Sound heard at midline or "everywhere" 1, 3

Rinne Test Procedure

1. Place the vibrating tuning fork over the mastoid bone of one ear 1, 3
2. Move the tuning fork to the entrance of the ear canal (not touching the ear) 1, 3
3. Ask where the sound is louder 2
4. Normal response: Sound heard better via air conduction (at the entrance to the ear canal) 1, 3
5. Repeat for the other ear 1

Interpretation

Weber Test Results

• Sound lateralizes to one ear: Either CHL in that ear OR SNHL in the opposite ear 1, 2
• Sound remains midline: Either normal hearing bilaterally or symmetric hearing loss 1

Rinne Test Results

• Air conduction > bone conduction (positive Rinne): Normal or SNHL 2
• Bone conduction > air conduction (negative Rinne): CHL in that ear 1, 2

Combined Interpretation Patterns

• Conductive hearing loss: Weber lateralizes to affected ear AND negative Rinne in affected ear 2
• Sensorineural hearing loss: Weber lateralizes to unaffected ear AND positive Rinne in both ears 2

Diagnostic Accuracy

The sensitivity of tuning fork tests ranges from 43-91% and specificity from 50-100% when compared to formal audiometry, with significant variability depending on technique and the degree of hearing loss. 4

• The Rinne test transitions from normal to abnormal at 13-40 dB of conductive hearing loss 4
• The Weber test transitions at 2.5-4 dB of asymmetry 4
• The 256 Hz fork is more sensitive for detecting conductive hearing loss, but the 512 Hz fork is recommended as the standard due to fewer false-positive responses 5

Critical Caveats and Pitfalls

Essential Precautions

• Remove impacted cerumen before testing, as it causes conductive hearing loss that confounds results 1, 2
• Perform testing in a quiet environment to minimize ambient noise interference 2
• Never substitute tuning fork tests for formal audiometry—they provide preliminary screening information only 3, 2

Common Diagnostic Errors

• Never assume conductive hearing loss without audiometric confirmation, as misdiagnosing sensorineural hearing loss as conductive can delay critical treatment, particularly in sudden sensorineural hearing loss requiring urgent intervention 2
• Patients cannot accurately distinguish subjective hearing loss as either CHL or SNHL based on symptoms alone, making objective testing essential 1
• Tuning fork tests have high risk of bias in patient selection and significant heterogeneity in reported accuracy 4

Clinical Context

When audiometric testing is not immediately available, tuning fork tests combined with otoscopic examination serve as the best bedside screening tools to preliminarily distinguish conductive from sensorineural hearing loss before formal testing. 2

• Patients with SNHL will almost always have a normal otoscopic examination, whereas patients with CHL will often show abnormalities 1
• An audiogram remains essential for definitive diagnosis, particularly for conditions like Ménière's disease where specific audiometric patterns are required 1
• The "hum test" (patient hums and reports which ear is louder) can substitute for the Weber test when a tuning fork is unavailable 3