Laboratory Studies
See the list below:
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A routine series of laboratory tests is not recommended in the evaluation of patients with hearing impairment. A rational assessment of the cost-benefit ratio and the clinician's index of suspicion dictate the selection of necessary laboratory studies to be performed for each individual patient.
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Studies may include the following:
Genetic testing, including connexin 26 gene mutation testing. (Patients with syndromic features benefit from a genetic evaluation. Clinical testing for many genes associated with hearing loss is available.)
CBC count with differential
Chemistries
Blood sugar
BUN/creatinine
Thyroid function studies
Urinalysis
Fluorescent treponemal antibody absorption (FTA-ABS)
Specific immunoglobulin M (IgM) assays for toxoplasmosis, rubella, cytomegalovirus, herpes virus, and autoimmune panel, eg, erythrocyte sedimentation rate (ESR), antinuclear antibody (ANA), rheumatoid factor (RF), complement levels, Raja cell studies, Western blot to identify a serum anti-68 KD autoantibody, and circulating immune complexes
Imaging Studies
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Computed tomography (CT) scanning
CT scanning offers very high-resolution images with 1-mm slices, allowing good visualization of the anatomy of the bones, ossicles, and inner ear.
CT scanning may be used to identify potentially surgically reparable causes of SNHL and may also be used to identify the less dysplastic, and presumably better hearing ear when considering auditory habilitation. CT abnormalities are found in up to 30% of individuals with hearing loss and thus are an important component of the evaluation. For example, enlarged vestibular aqueduct and Mondini malformation are common findings in Pendred syndrome.
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Magnetic resonance imaging (MRI): High soft tissue contrast makes MRI ideal for evaluation of the inner ear, internal auditory canal, and cerebellopontine angle.
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Renal ultrasonography: Consider renal ultrasonography when abnormalities are suspected.
Other Tests
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Valid and reliable techniques are available to determine the presence, degree, and nature of hearing impairment in children as early as the first 24 hours of life. Such techniques include the following:
Auditory brainstem response
Audiometry
Tympanometry
Acoustic reflex threshold measurement
Otoacoustic emissions (OAE)
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Electrocardiography: Consider ECG as a means to reveal cardiac conduction anomalies when an appropriate degree of clinical suspicion is present.
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Electrooculography can identify retinitis pigmentosa earlier than a physical examination.
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Inner ear.
