The end of classifying and describing hearing loss based on the pure tone audiogram.
We audiologists sometimes do things that need a bit of rethinking.
We see patients every day. We sympathize with their struggles and try to make a difference to their lives and the lives of their significant others. That is why we became audiologists. I believe that if we want to improve quality of lives, we need to reconsider how we test and classify hearing loss.
I cannot remember having ever heard a patient complain about their threshold for pure tones at 2 kHz. Nevertheless, that is often one of the first things we do. After the intake, we administer the pure tone audiogram. With beeps. Under headphones. For the left and right ear separately. Well, feel free to do that and stop there if this is the complaint of your patient. If not, read on.
We do not communicate in beeps. We do not listen with our ears separately. There are not many beeps in nature. The threshold of beeps only gives you a physical measure of how soft the softest beeps can be to be heard. Yet, this whole beep concept seems to be enough to classify a patient’s degree of hearing loss. From mild, to moderate, severe and profound. I think that is odd.
Yes, we need the pure tone audiogram if we want to fit hearing aids. But we are not audiologists to fit hearing aids only. Ideally we would understand, express and classify hearing loss in a way which is closer to what patients experience in daily life and what triggers them to seek help and where we can make truly a difference.
Most patients walk through your clinic door after an emotional event. That trigger has very often to do with their frustration understanding speech in noise — a conversation that mattered…a school presentation by a granddaughter…a eulogy at a funeral…a conversation about a medical test result at the GP…a Christmas dinner with the family. And, it was not understood well because of background noise. There is a key dimension in physics that describes the problem —the signal-to-noise ratio. And with an appropriate test, the loss in signal-to-noise ratio compared to normal hearing listeners of the same age can be measured. A speech-in-noise test. For both ears at the same time. Corrected for the loss of sensitivity of the ears. Recreating a 3-dimensional space like in real life. But with high test-retest reliability and with age-related normative data.
That test exists. Not any speech-in-noise test, but the LiSN-S PGA test, developed by Harvey Dillon and Sharon Cameron at NAL in Australia. It is, in my mind, the textbook example of how a diagnostic test should be designed. Administering takes just 5 minutes. And the beauty is that at the end of the test you get just one single but powerful number – your patient’s hearing loss in a signal-to-noise ratio, compared to normal hearing listeners of the same age. One single number. This should be the way to express any degree of hearing loss, as it reflects the key problem people with hearing loss are struggling with, and it immediately leads to clear clinical recommendations as to what interventions should be considered.
The pure tone audiogram only tells you how much gain and output is required. Not unimportant, but not a big deal either. The speech-in-noise test gives you a signal-to-noise ratio that falls into three categories:
A loss of up to three dB, you are still fine. Maybe you need amplification to compensate for your loss in sensitivity, but with that amplification you should be able to function quite well.
A loss of 3 to 6 dB in signal-to-noise ratio means you need advanced directional microphone technology to boost your speech understanding in noisy places. Directional microphones are known to give about this amount of improvement in signal-to-noise ratio, provided the distance between talker and listener is not much more than the critical distance of the room.
If the loss in signal-to-noise ratio is more than 6 dB, only advanced wireless microphone technology will be able to give a performance increase that will bring the patient close to their normal hearing peers. (In fact, with Roger technology, they can sometimes understand speech better than their normal hearing peers, but that is not the topic of this blog post.)
If we adopt this new classification, we will also get rid of the term ‘mild hearing loss’. In my mind, there is no such thing as a mild hearing loss. It is the wrong expression and gives patients and their significant others an excuse not to do anything because it is only mild. It is simply based on the wrong metric.
Maybe we need some time to get rid of the current definition of the degrees of hearing loss. After all, even the WHO adheres to this pure tone audiogram based classification. But, if we all cease to talk about mild hearing loss, and instead call it a sensorineural hearing loss, or a mixed or conductive hearing loss, whatever the case is, the tone of the conversation is already different.
To learn more about the LiSN-S PGA test go to https://www.phonakpro.com/com/en/resources/fitting-and-tests/lisn-s-test/overview-lisn-s.html.