In the context of glue ear, a tympanometry test primarily shows the presence of fluid in the middle ear and the resulting lack of mobility in the eardrum. Unlike a standard hearing test that measures what a child can hear, tympanometry is an objective test of middle ear function. It measures how the eardrum responds to changes in air pressure. When glue ear is present, the fluid behind the eardrum prevents it from vibrating or moving normally, which is represented on a graph as a characteristic flat line known as a Type B tympanogram.
What We Will Cover in This Article
- The mechanics of how a tympanometer measures ear pressure
- Visualising the differences between Type A, B, and C graphs
- Why a flat line (Type B) is the definitive marker for glue ear
- Understanding the role of negative pressure (Type C)
- How clinicians use these results to determine treatment urgency
- What happens when a test shows a normal result despite hearing concerns
The Mechanics of the Test
Tympanometry works by changing the air pressure in the ear canal to see how the eardrum reacts.
During the test, a small probe is placed at the entrance of the ear. It sends a quiet tone into the ear while simultaneously changing the air pressure. A healthy eardrum, which has air behind it, will move easily when the pressure is balanced. The device records this movement and plots it on a graph where the vertical axis represents compliance and the horizontal axis represents air pressure.
Interpreting the Graphs
Audiologists categorise the results into three main types based on the shape of the curve on the graph.
Type A: Normal Function
A Type A result looks like a tent or a sharp mountain peak in the centre of the graph. This indicates that the middle ear is filled with air and the eardrum is moving perfectly at normal atmospheric pressure. This result effectively rules out glue ear at the time of the test.
Type B: The Glue Ear Profile
Type C: Negative Pressure
A Type C result shows a peak, but it is shifted significantly to the left side of the graph. This indicates negative pressure in the middle ear, often caused by a blocked Eustachian tube. This is frequently seen at the very beginning of a glue ear episode or when the condition is starting to resolve.
Why the Peak Height Matters
Even if a peak is present, its height gives the clinician clues about the state of the ear. A very low peak may suggest that fluid is beginning to accumulate or that the fluid is very thick, while a normal height peak shifted to the left suggests that while there is no fluid yet, the ear is not ventilating properly.
Clinical Decisions Based on Results
The results of the tympanometry test are the primary factor in deciding the next clinical steps in the UK.
- Single Type B Result: Usually leads to the start of a three month watchful waiting period to see if the fluid clears naturally.
- Persistent Type B Result: If the graph remains flat after three months and is accompanied by hearing loss, a referral to an ENT specialist for potential grommet surgery is usually the next step.
- Fluctuating Results: If a child moves between Type B and Type C, it suggests the Eustachian tube is trying to function, and the clinician may allow more time for natural recovery.
To Summarise
A tympanometry test is the most reliable way to confirm glue ear by showing a flat Type B graph. This result objectively demonstrates that the middle ear is filled with fluid and the eardrum is unable to vibrate. By identifying whether the ear has healthy air pressure, negative pressure, or fluid blockage, clinicians can accurately monitor a child progress and determine when medical or surgical intervention is necessary to restore hearing.
If your child recent ear check showed a flat line on the graph, the next clinical step is to record this as the start of the observation period and schedule a repeat test in twelve weeks to check for improvement.
Can a child fail a tympanometry test but still have normal hearing?
It is rare. Usually, a flat Type B result coincides with at least a mild conductive hearing loss because the stiff eardrum cannot pass sound through to the inner ear effectively.
What if the test is flat but my child has no pain?
This is very common. Glue ear is typically a painless condition. The flat line measures fluid and pressure, not infection or pain levels.
Does a flat line always mean glue ear?
In children, it almost always does. However, a flat line can also occur if there is a hole in the eardrum or if the ear canal is completely blocked with wax, which is why a visual check is always done first.
Can the test be done if the child is crying?
Crying or moving can interfere with the seal of the probe, making it difficult to get an accurate reading. The child needs to be relatively still and quiet for the few seconds the test takes.
Is Type C better than Type B?
Clinically, yes. Type C means there is still air in the ear, even if the pressure is wrong. It suggests the ear is not completely blocked with fluid yet or is in the process of clearing.
How often should tympanometry be repeated?
In the UK, it is typically repeated every three months during the watchful waiting period to track whether the fluid is persisting or resolving.
Authority Snapshot
This article was reviewed by Dr. Rebecca Fernandez, a UK trained physician with an MBBS and extensive experience in inpatient and outpatient clinical care. Dr. Fernandez specialises in evidence based treatment planning and the use of objective diagnostic tools like tympanometry to monitor paediatric health. She has a strong background in managing acute cases and helping families navigate specialised clinical pathways.
