How to Read Pure Tone Audiometry (PTA) – Part 1

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.