Pure Tone Audiometry (PTA)
Pure Tone Audiometry is the gold standard subjective test used to determine the hearing threshold sensitivity of an individual. It provides a graphical representation of a patient’s hearing, known as an audiogram.
Key Concepts
- Frequency (Hz): Tested typically between 250 Hz and 8,000 Hz.
- Intensity (dB HL): The hearing level (HL) is measured in decibels, with 0 dB HL representing the standard threshold of normal human hearing.
- Air Conduction (AC): Tests the entire auditory pathway (external, middle, and inner ear).
- Bone Conduction (BC): Tests the inner ear directly by bypassing the external and middle ear.
Interpreting the Audiogram
| Finding | Description |
|---|---|
| Normal Hearing | Both AC and BC thresholds are ≤ 25 dB HL. |
| Conductive Loss | BC is normal; AC shows elevation. Significant Air-Bone Gap (ABG). |
| Sensorineural Loss | Both AC and BC are elevated; AC and BC thresholds are similar (no ABG). |
High-Yield Exam Pearl:
- Air-Bone Gap (ABG): An ABG of >10 dB is clinically significant and indicates pathology in the conductive mechanism (e.g., ossicular disruption, otosclerosis, or middle ear effusion).
- Carhart’s Notch: A classic finding in otosclerosis, showing a dip in bone conduction thresholds specifically at 2,000 Hz.