Hearing Disorders and Deafness - Diagnosis 

Doctors should screen for hearing problems during regular checkups, but hearing loss generally needs to be evaluated by an otolaryngologist—a  doctor who specializes in the care of the ear. An audiologist is  a trained professional who tests hearing and performs hearing evaluation tests that measure the degree of hearing loss and the particular sound frequencies that are impaired. If hearing loss is present, other tests help determine how much the hearing loss affects the person's ability  to understand speech and whether the hearing loss is sensorineural, conductive, or mixed. Some hearing tests also help identify possible causes of hearing loss. Although many hearing tests require the person's active participation, some do not. 

Sudden deafness is  an emergency that requires immediate evaluation by a specialist. Blood tests are performed and, rarely, exploratory surgery is necessary. 

First, a doctor examines the ears. Using a hand-held otoscope, the doctor looks to make sure the ear canal is completely open. The otoscope also allows the doctor to see the eardrum, which helps determine whether a middle-ear infection is present or whether fluid has accumulated behind the eardrum. Sometimes doctors screen for hearing loss using a hand-held tone generator. Some combination  of the following tests is usually needed to better understand the hearing loss, determine its cause, and direct treatment. 

Audiometry is the first step in hearing testing. In this test, a person wears headphones that play tones of different frequency (pitch) and loudness into one ear or the other. The person signals when a tone is heard, usually by raising the corresponding hand. For each pitch, the test identifies the quietest tone the person  can hear in each ear. The results are presented in comparison  to what is considered normal hearing. Because loud tones presented to  one ear may also be heard by the other ear,  a sound other than the test tone (usually white noise) is presented  to the ear not being tested. 

Speech threshold audiometry measures  how loudly  words have to be  spoken to be understood. A person listens to a series of two-syllable, equally accented words (spondees), such as "railroad," "stairway," and "baseball," presented at different volumes. The volume at which the person can correctly repeat half of the words (spondee threshold) is recorded. 

Discrimination, the  ability to hear differences between words that sound similar, is tested by presenting pairs of similar one-syllable words. The percentage of words correctly repeated is the discrimination score. People with a conductive hearing loss usually have a normal discrimination score, although at a higher volume. People with sensorineural hearing loss often have abnormal discrimination at all volumes. 

Tympanometry tests how well sound can pass through the eardrum  and middle ear. This test does not require  the active participation  of the person being tested and is commonly used in children. A device containing  a microphone and a sound source is placed snugly in the ear canal, and sound waves are bounced off the eardrum as the device varies the pressure in the ear canal. Abnormal tympanometry results suggest a conductive type of  hearing loss. 

The Rinne tuning fork test is a screening test that helps distinguish between conductive and sensorineural hearing loss. This test compares how well a person hears sounds  conducted by air with how well the person hears sounds conducted by the skull bones. To test hearing by air conduction, the tuning fork is placed near the ear. To test hearing by bone conduction, the base of a vibrating tuning fork is placed against the head so the sound bypasses the middle  ear and goes directly to the nerve cells of the inner ear. If hearing by air conduction is reduced but hearing by bone conduction is normal, the hearing loss is conductive. If both air and bone conduction hearing are reduced, the hearing loss is sensorineural or mixed. People with sensorineural hearing loss may need further evaluation to look for other conditions, such as Meniere's disease or brain tumors. 

Auditory brain stem response is  a test that measures nerve impulses in the brain stem resulting from sound signals in the ears.  The information helps determine what kind  of signals the brain is receiving from the ears. Test results are abnormal in people with some sensorineural types  of hearing loss and in people with many types of brain tumors. Auditory brain stem response is used  to test infants and also can be used to monitor certain brain functions in people who are comatose or undergoing brain surgery. 

Electrocochleography measures  the activity of the cochlea and the auditory nerve by means of an electrode placed on, or through, the eardrum. This test and the auditory brain stem response can be used to measure hearing in people who cannot or will not respond voluntarily to  sound. For example, these tests are used  to find out whether infants and very young children have profound hearing loss (deafness) and whether a person is faking or exaggerating hearing loss (psychogenic hypacusis). 

Otoacoustic emissions testing uses sound to stimulate the inner ear (cochlea).  The ear itself then generates a very low-intensity sound that matches the stimulus. These cochlear emissions are recorded using sophisticated electronics and are used routinely in many nurseries to screen newborns for congenital hearing loss. This test is  also used in adults to help determine the reason for a  hearing loss. 

Other tests can measure the ability to interpret and understand distorted speech, understand a message presented to one ear when a competing message is presented to the other ear, fuse incomplete messages to each ear into a meaningful message, and determine where a sound is coming from when it is presented to both ears at the same time. Depending on the person's symptoms and the results of the hearing tests, some people need computed tomography (CT) or magnetic resonance imaging (MRI) to look for tumors invading structures of the ear or blocking the eustachian tube.