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EN2.4 | Audiogram and Impedance Interpretation — SDL Guide (Part 3)
Self-Assessment: Audiometry Interpretation Competency Check
Apply the interpretation framework from this SDL to answer these self-check questions. For each question, state your reasoning before reading the explanation.
Q1: An audiogram shows: right AC threshold 50 dB at all frequencies; right BC threshold 10 dB at all frequencies. What is the ABG, what type of hearing loss is this, and what is the PTA?
Answer: ABG = 50 − 10 = 40 dB (large air-bone gap). Type = RIGHT CONDUCTIVE HEARING LOSS (AC elevated, BC normal). PTA = average of AC at 500, 1000, 2000 Hz = 50 dB HL = MODERATE hearing loss.
Q2: A tympanogram shows a flat (Type B) curve with a very large ear canal volume (3.5 mL, vs normal 0.9–2.5 mL). What does this indicate?
Answer: A flat (Type B) tympanogram with large canal volume indicates a TM perforation — the probe tip is communicating with the middle ear and mastoid air cell system through the perforation, registering a large volume. This is the key distinction from OME (glue ear), which also gives Type B but with NORMAL canal volume (the fluid-filled middle ear is a closed space).
Q3: A patient has bilateral SNHL. The audiogram shows BC thresholds of 60 dB at 4000 Hz and 25 dB at 500 Hz bilaterally, with no ABG at any frequency. The PTA (at 500, 1000, 2000 Hz) is 30 dB bilaterally. What is the severity of the hearing loss in the speech frequencies, and what configuration is this?
Answer: PTA 30 dB = MILD hearing loss in the speech frequencies. The configuration is a HIGH-FREQUENCY SLOPING SNHL (good at low frequencies, poor at high frequencies) — consistent with presbycusis or noise-induced hearing loss (check for a 4 kHz notch).
| Audiogram finding | Type of hearing loss | Tympanogram correlate |
|---|---|---|
| AC elevated, BC normal, ABG >15 dB | Conductive | Type B (effusion), Type As (otosclerosis), Type Ad (discontinuity) |
| AC = BC both elevated, no ABG | Sensorineural | Type A (normal middle ear) |
| AC and BC both elevated, ABG >15 dB | Mixed | Type A or Type B depending on cause |
| 4 kHz notch on SNHL | Noise-induced hearing loss | Type A |
| Low-frequency SNHL | Meniere's disease (early) | Type A |
| Type B flat, large canal volume | TM perforation | — |
| Type B flat, normal canal volume | Otitis media with effusion | — |
SELF-CHECK
A 45-year-old male has right-sided hearing loss. Audiogram right ear: AC thresholds 55 dB at all frequencies; BC thresholds 55 dB at all frequencies. No air-bone gap. Tympanogram right: Type A. This pattern is consistent with:
A. Right conductive hearing loss due to wax impaction
B. Right sensorineural hearing loss
C. Right mixed hearing loss
D. Normal hearing in the right ear
Reveal Answer
Answer: B. Right sensorineural hearing loss
No air-bone gap (AC = BC = 55 dB HL) + Type A tympanogram = RIGHT SENSORINEURAL HEARING LOSS. Both AC and BC are equally elevated because the cochlea is damaged — the outer and middle ear are structurally intact (Type A tympanogram, no ABG), confirming the problem is at the cochlear level or beyond. Conductive loss requires an ABG (AC elevated, BC normal). A 55 dB HL PTA = moderately severe hearing loss requiring investigation for cause (acoustic neuroma, SSHL, Meniere's).