Pure tone audiometry (PTA) measures hearing sensitivity and is represented on an audiogram, a graph showing the softest sounds a person can hear at various frequencies. Here’s a step-by-step guide to reading and interpreting pure tone audiometry results:
Step 1: Understand the Audiogram
• X-axis:
Represents frequencies (pitches) in hertz (Hz), typically ranging from 250 Hz to 8000 Hz.
• Low frequencies (bass sounds) are on the left.
• High frequencies (treble sounds) are on the right.
• Y-axis:
Represents hearing thresholds (loudness) in decibels hearing level (dB HL).
• The top of the graph represents soft sounds (better hearing).
• The bottom represents louder sounds (poorer hearing).
Step 2: Know the Symbols
1. Air Conduction (AC):
• Red O: Right ear.
• Blue X: Left ear.
• These measure how sounds are transmitted through the outer, middle, and inner ear.
2. Bone Conduction (BC):
• Red <: Right ear.
• Blue >: Left ear.
• These bypass the outer and middle ear to assess inner ear (cochlear) function.
3. Masked symbols
(e.g., [ ] or Δ) are used when masking is applied to isolate one ear during testing.
Step 3: Look for Hearing Thresholds
Hearing thresholds are the lowest intensity levels at which a person hears a sound 50% of the time. Compare the thresholds across frequencies.
Hearing Ranges:
• Normal hearing: 0–25 dB HL.
• Mild hearing loss: 26–40 dB HL.
• Moderate hearing loss: 41–55 dB HL.
• Moderately severe hearing loss: 56–70 dB HL.
• Severe hearing loss: 71–90 dB HL.
• Profound hearing loss: 91+ dB HL.
Step 4: Identify the Type of Hearing Loss
Compare air conduction (AC) and bone conduction (BC) thresholds:
1. Normal Hearing:
AC and BC thresholds are within the normal range (0–25 dB HL).
2. Conductive Hearing Loss:
BC thresholds are normal, but AC thresholds are elevated (air-bone gap present). This indicates an issue in the outer or middle ear.
3. Sensorineural Hearing Loss:
Both AC and BC thresholds are elevated, and they overlap (no air-bone gap). This suggests an issue in the cochlea or auditory nerve.
4. Mixed Hearing Loss:
Both AC and BC thresholds are elevated, but an air-bone gap is present. This indicates combined outer/middle ear and inner ear problems.
Step 5: Analyze the Configuration (Shape)
Patterns on the audiogram can indicate specific conditions:
• Flat: Hearing loss is relatively uniform across frequencies.
• Sloping: Hearing loss worsens at higher frequencies, common in age-related hearing loss (presbycusis).
• Rising: Better hearing at higher frequencies, often seen in middle ear issues.
• Notched: A dip in hearing sensitivity at certain frequencies, typically 3000–6000 Hz, often due to noise exposure.
• Cookie-bite: Mid-frequency hearing loss, often congenital or genetic.
• Corner: Hearing loss only in the low frequencies with no response at higher frequencies, seen in severe or profound hearing loss.
Step 6: Consider Speech Audiometry
• Speech Reception Threshold (SRT): The lowest intensity at which speech can be understood. Should correlate with PTA averages (500, 1000, and 2000 Hz thresholds).
• Word Recognition Score (WRS): Measures clarity of speech. A poor score with normal thresholds may indicate neural or central auditory issues.
Step 7: Match Results to the Patient’s Symptoms
Combine the audiogram findings with patient complaints to confirm the diagnosis and guide treatment. For example:
• Difficulty understanding speech in noise may correlate with high-frequency hearing loss.
• A sudden drop at one frequency could indicate trauma or Meniere’s disease.