Spontaneous otoacoustic emissions (SOAE) are sounds produced by the ear without any external sound source, and they can be detected using microphones inserted into the external ear canal. These emissions typically range in frequency from 500 Hz to 4,500 Hz.

Evoked OAE (EOAE), require an acoustic stimulus prior to their measurement or emission. There are three types of EOAEs: transient evoked, stimulus-frequency, and distortion product OAEs. Transient evoked and distortion product OAEs are the two most used clinically.

Transient-evoked OAE (TEOAE) are elicited using either a click or tone-burst stimuli. A click stimulus possesses a sudden onset, brief duration, and spans a wide frequency range up to 4 kHz, aiming to evoke responses from multiple nerve fibers. In contrast, tone burst stimuli are delivered within a narrower frequency range, especially at lower frequencies, to elicit more frequency-specific responses.

Detecting a response when testing TEOAEs can be difficult as the response emission mirrors the stimulus frequency. Thus, multiple stimuli and responses are elicited and averaged to distinguish the emission from the stimulus. Response emissions exhibit latency periods ranging from 2 to 23 milliseconds, corresponding to the frequency of the stimulus. Higher frequencies, which travel shorter distances along the basilar membrane to the base, exhibit shorter latencies, while lower frequencies, traveling further towards the cochlear apex, require longer latencies.

Stimulus-frequency OAEs (SFOAEs) are evoked using pure tone stimuli. Like TEOAEs, the response emission is the same frequency as the stimulus, making responses difficult to distinguish. As a result, this type of OAE is rarely used clinically.

Distortion-product OAE (DPOAEs) are elicited by employing two concurrent pure tone stimuli (f1 and f2). The main test frequency is referred to as f2 whereas f1 is determined by a fixed ratio in reference to f2.

In contrast to TEOAE, which offers a comprehensive assessment of cochlear function across a wide frequency spectrum, DPOAE can be tailored to evaluate frequencies aligned with the patient’s audiogram, thereby enhancing sensitivity in detecting high-frequency hearing impairments.

When measuring the DPOAE, the largest response emission should occur at the frequency calculated from the formula: 2f1-f2. This makes DPOAEs easily distinguishable from the presented stimuli as the resulting frequency is different from the two presented stimuli. Typically, DPOAEs are recorded at 1-6k Hz, but they can be elicited at frequencies as high as 10-12k Hz depending on the equipment used.

NIHL occurs due to prolonged exposure to loud noises, resulting in damage to the hair cells in the inner ear. OAEs are sounds generated by the cochlea in response to external stimuli, such as sound. In individuals with healthy hearing, OAEs are typically present, indicating normal cochlear function. However, in cases of NIHL, where there is damage to the cochlear hair cells, OAEs may be diminished or absent. This damage may precede hearing loss that can be detected with pure tone audiometry. Therefore, OAE testing can aid in the early detection and monitoring of NIHL by assessing the integrity of the cochlear function. This information is crucial for implementing preventive measures and interventions to mitigate further hearing loss in individuals exposed to hazardous noise levels. 

Ototoxic drugs, like certain antibiotics and chemotherapy agents, primarily affect the outer hair cells and can be detected through OAE testing before abnormalities appear on a traditional audiogram. OAE testing offers rapid application and cost-effectiveness, making it a practical choice for monitoring patients throughout their treatment journey. Distortion-product OAEs (DPOAEs) are particularly sensitive to changes in higher frequencies, which are often the first to be affected by ototoxicity. Before initiating ototoxic medications, patients typically undergo baseline OAE testing, with subsequent tests conducted after each dose. A decrease of 2.4 dB or more in OAE amplitude is considered significant, indicating a change in cochlear function and prompting further evaluation. 

Newborn hearing screening has become a routine practice in hospitals across the country, serving as the standard of care. Its primary goal is to identify newborns who may have hearing impairments and thus need further assessment. Additionally, it aims to detect infants with medical conditions that might lead to delayed onset hearing loss, enabling the development of ongoing monitoring strategies for their hearing health. 

Otoacoustic emissions (OAE) are often used for newborn hearing screenings due to their efficiency and reliability in detecting potential hearing impairments shortly after birth. OAE testing is non-invasive, quick, and can be performed while the infant sleeps, making it particularly suitable for screening newborns. Additionally, OAEs provide objective measures of cochlear function, allowing for early identification of hearing loss even before infants can respond to sound through behavioral testing. This early detection facilitates timely intervention and support, crucial for ensuring optimal language and cognitive development in newborns.

As OAE tests measure the peripheral auditory system, retrocochlear issues typically manifest with normal OAE results alongside abnormal audiograms and auditory brainstem responses (ABR). Auditory neuropathy spectrum disorder (ANSD) is a retrocochlear disorder often diagnosed and monitored with OAE testing. ANSD often presents with abnormal or absent ABR, poor word recognition, and absent stapedial reflexes. However, OAE may be absent if retrocochlear masses compress the internal auditory artery, impeding blood flow to the cochlea. Additionally, OAE might diminish over time in ANSD patients. 

Assessing the accuracy of hearing tests depends on various factors including the specific test utilized, the population being tested, and the methodology employed. According to a study published in the Journal of the American Academy of Audiology, distortion product otoacoustic emissions (DPOAEs) have been found to be highly accurate in detecting cochlear dysfunction, with reported sensitivities ranging from 70% to 100% and specificities ranging from 80% to 100%. For TEOAEs, when used in newborn hearing screening, a 66.7% sensitivity and 98.8% specificity has been noted. 

However, it's important to note that the accuracy of these tests may vary depending on factors such as the experience of the clinician administering the test, the age and cognitive abilities of the patient, and the presence of comorbid conditions. Therefore, while OAEs are generally considered accurate diagnostic tools, interpreting their results within the context of the individual patient's clinical presentation is essential for ensuring accurate diagnosis and appropriate management. 

Reading otoacoustic emissions (OAE) test results involves interpreting the presence or absence of emissions and assessing their amplitude and reproducibility. When analyzing OAEs, audiologists typically look for a clear presence of emissions in response to stimuli presented to the ear. Absence of emissions may indicate cochlear dysfunction or hearing loss. Additionally, the amplitude of the emissions provides information about cochlear function, with higher amplitudes generally associated with healthier cochlear function. Reproducibility of emissions across multiple presentations of the stimulus is also crucial, as it ensures reliability of the results. Interpretation of OAE test results should be done in conjunction with patient history, clinical observations, and other diagnostic tests to provide a comprehensive assessment of hearing function.