In an audiogram, a bone conduction threshold of 20 dB HL and air conduction threshold of 50 dB HL at 2 kHz indicates which type of hearing loss?

Explanation

## Audiogram Interpretation: Air-Bone Gap **Key Point:** The difference between air conduction (AC) and bone conduction (BC) thresholds defines the type of hearing loss. ### Air-Bone Gap Analysis When AC threshold is worse (higher dB) than BC threshold, an **air-bone gap** exists. | Condition | AC Threshold | BC Threshold | Gap | Type | |-----------|--------------|--------------|-----|------| | Normal | ≤20 dB HL | ≤20 dB HL | <10 dB | Normal | | Conductive loss | Elevated | Normal | >10 dB | **Conductive** | | Sensorineural loss | Elevated | Elevated equally | <10 dB | Sensorineural | | Mixed loss | Elevated | Elevated (less than AC) | >10 dB | Mixed | ### In This Case - **BC = 20 dB HL** (normal) - **AC = 50 dB HL** (elevated) - **Air-bone gap = 50 − 20 = 30 dB** (>10 dB) **High-Yield:** A gap >10 dB indicates conductive pathology. The inner ear (cochlea) is intact, so BC is normal. The problem lies in sound transmission through the middle ear (ossicles, tympanic membrane, Eustachian tube). **Clinical Pearl:** Common causes of conductive loss with this pattern: otitis media with effusion, ossicular fixation (otosclerosis), tympanic membrane perforation, cerumen impaction. **Mnemonic:** **ABC rule** — Air-Bone gap indicates Conductive loss.