The Fowler test is an audiometric test that checks the loudness perception in side-differentiated hearing loss. Most often, the test procedure takes place to diagnose recruitment, that is, hearing loss involving the inner ear, or is used to differentiate between sensorineural and conductive hearing loss. Because the Fowler test involves a subjective loudness compensation procedure, the method is only suitable for use on people who are willing to cooperate and are mentally healthy.
What is the Fowler test?
The Fowler test is an audiometric test that checks the loudness perception in side-differentiated hearing loss. The Fowler test is an otolaryngology testing procedure. The procedure is also known as the ABLB test or Alternate Binaural Loudness Balance test. It is an audiometric method that compares the loudness perception of both ears using alternating sounds of different levels. For a long time, the recruitment detectable by the test was considered a differential diagnostic tool for the undoubted confirmation of sensorineural hearing loss. Otolaryngology has been familiar with the Fowler test procedure since 1937, when Edmund P. Fowler first published the test principles. Since the test relies on the cooperation of the patient and the patient’s subjective perception of loudness strongly influences the results, it cannot be called an objective assessment procedure. Instead, with regard to the test basis, one speaks of a subjective loudness compensation for side-differentiated hearing loss.
Function, effect, and goals
Most commonly, the Fowler test occurs in unilateral or extremely side-differentiated hearing loss. As a rule, the procedure is used only when there is a difference of at least 30 dB between the two ears in terms of hearing loss. In this context, the test is primarily used for differential diagnosis of sensorineural and conductive hearing loss. The patient’s subjective perception of loudness determines the settings made by the staff on the audiometer. For this reason, the Fowler test can only be performed on patients who are willing to cooperate. In conclusion, the procedure is not suitable for unwilling or mentally insane test subjects. The Fowler test can be used to determine the location of a sensorineural hearing loss in inner ear disorders, such as recruitment. To perform the test, a sound audiometer is needed. This device must also be able to play a tone of different level to both ears alternately. For this reason, the Fowler test is usually performed only in ENT clinics specially equipped for this purpose. At the beginning of the test, the staff adjusts the level of the audiometer so that the patient has the impression of equal loudness in both ears. The test personnel repeat this procedure with different levels, ranging from the hearing threshold to the pain threshold. An entry level of 20 dB above the hearing threshold is now considered recommended, which is first set to the worse ear and then leveled to the better ear. The series of tests then continues in 20-dB increments at a time, and the results are recorded on a sound audiogram form that is evaluated by the staff at the conclusion of the testing procedure. If the evaluation reveals a consistent ratio of loudness perception at the hearing threshold as well as for suprathreshold sounds, then a conductive hearing loss with an intact inner ear is usually present. This would be the case, for example, if the difference in hearing thresholds in both ears is continuously 20 dB and remains unchanged above the hearing threshold. If, on the other hand, there is inner ear involvement, i.e., recruitment, an increasing level usually changes something about the loudness difference between the two ears. The higher the level, the smaller the difference in loudness perception in the case of recruitment. Above a certain level, the difference usually evens out completely and both ears have the same loudness impression again. If, instead of recruitment, an auditory nerve damage or a retrocochlear cause is present, the difference in loudness perception either remains or multiplies with increasing level.
Risks, side effects and dangers
The Fowler test is a non-invasive testing procedure that is generally not associated with any risks or side effects for the patient. In rare cases, the upper levels at the pain threshold may cause a temporary buzzing in the ears that is entirely harmless. Over the course of the day, this reaction evens out again and the buzzing fades. An even rarer, but under certain circumstances conceivable reaction to the test procedure is a slight headache, which remains for the rest of the day, but, like the buzzing, has passed by the following day at the latest. The Fowler test procedure takes less than an hour and does not require hospitalization or medication. Apart from an explanatory preliminary talk, the test does not require any special preparatory measures. After the test procedure and the evaluation of the results by the staff, the patient can go home again. Sometimes additional test methods are ordered in the following weeks, usually for further differential diagnosis. Under certain circumstances, the Fowler test can lead to false results. This is mainly due to the subjective basis of the test. How reliable the test result ultimately is is determined by the patient himself, so to speak. For this reason, ear, nose and throat specialists do not usually use the Fowler test with mentally confused patients and small children, because no meaningful results can be expected for these patients. For the Fowler test to provide meaningful and reliable results, the patient must understand the basis of the test and be able to actively participate in performing the procedure.
