Pure Tone Audiometry

Pure tone audiometry is a fundamental hearing test used to evaluate an individual’s auditory sensitivity. This test is critical for identifying and grading hearing loss. It is conducted in a soundproof environment to determine the lowest sound levels a person can detect across frequencies ranging from 0.25 to 8 kHz. The obtained hearing threshold levels reveal the type and severity of the loss, guiding the formulation of appropriate treatment and intervention plans. This test, which is an extremely valuable tool for preserving and rehabilitating hearing health, provides important information that enhances the quality of life of individuals.

What Is Pure Tone Audiometry and How Does It Evaluate Hearing?

Pure tone audiometry is one of the most commonly used, reliable, and fundamental audiological methods for evaluating an individual’s hearing health. The test aims to measure a person’s auditory sensitivity using pure tones—sinusoidal waves without harmonics. These tones are typically presented at frequencies ranging from 0.25 to 8 kHz, and the lowest sound intensity that the person can detect, i.e. the hearing threshold, is determined. Pure tone audiometry plays a critical role in understanding the degree, type, and possible causes of hearing loss.

During the test, for air conduction evaluations, headphones or in-ear devices are used, and for bone conduction analyses, a bone vibrator is placed on the mastoid bone. These two measurement methods play a key role in determining whether the hearing loss is of the conductive type—associated with outer or middle ear problems—or sensorineural, originating from the inner ear or auditory nerve. In addition, a graphical result called an audiogram is obtained; this graph visually presents the hearing thresholds at different frequencies for each ear.

The audiogram is an important tool for understanding the extent and profile of an individual’s hearing loss. For example, it can show specific patterns characteristic of age-related or noise-induced hearing losses. These evaluation results help in the personalized planning of hearing aid recommendations, surgical interventions, or rehabilitation strategies.

How Is Pure Tone Audiometry Performed?

Pure tone audiometry is performed using a carefully planned procedure. The test includes specific steps to minimize factors that might affect the patient’s hearing health and to obtain reliable results. First, an otoscopic examination is conducted to inspect the ear canals. This step aims to identify conditions such as earwax or anatomical obstructions that could affect the hearing test. Then, the patient is seated comfortably in a position that prevents them from looking directly at the audiometer.

Before the test, detailed instructions are provided to the patient. They are told to respond as soon as they detect even the faintest sound—a critical step in accurately determining the hearing thresholds. During the air conduction test, special headphones are placed on the ears and pure tones are presented at various frequencies ranging from 250 Hz to 8,000 Hz. By gradually decreasing or increasing the sound, the lowest sound level that the patient can detect is determined. The bone conduction test is performed in a similar manner using a bone vibrator, which directly evaluates the function of the cochlea.

If there is a significant threshold difference between the ears, a technique called masking may be applied for an accurate measurement. Masking involves presenting noise to the non-test ear to determine the true hearing level of the tested ear. The results are then recorded in an audiogram. Regardless of the test technique, standardized symbols for both air and bone conduction thresholds for each ear can be displayed on a single graph.

What Types of Hearing Loss Can Be Determined by Pure Tone Audiometry?

Pure tone audiometry is a basic diagnostic method used to differentiate between types of hearing loss. By measuring the thresholds for air and bone conduction, this test helps determine whether the hearing loss is conductive, sensorineural, or mixed.

In conductive hearing loss, the bone conduction thresholds are normal while the air conduction thresholds are elevated. In this case, the difference between the air and bone thresholds—known as the air-bone gap—is usually 15 dB or more. These findings indicate a problem in the outer or middle ear, typically caused by conditions such as blockage, infection, or eardrum issues.

In sensorineural hearing loss, both the air and bone conduction thresholds are elevated, but there is no significant difference between them. This situation indicates damage in the inner ear or auditory nerve. It is commonly seen in conditions such as age-related hearing loss (presbyacusis) and adversely affects speech comprehension.

In mixed hearing loss, both air and bone conduction thresholds are elevated, and the difference between them is greater than 10 dB. This indicates that there are issues in both the outer/middle ear and the inner ear or auditory nerve.

Why Is Pure Tone Audiometry Considered the Gold Standard in Hearing Evaluation?

Pure tone audiometry (PTA) has long been considered the gold standard for evaluating hearing loss due to its reliability and accuracy. PTA measures hearing thresholds through both air and bone conduction, thus having the capacity to differentiate between conductive, sensorineural, and mixed hearing losses. This capability plays a critical role in diagnosing by analyzing different types of hearing loss in detail.

The accuracy of PTA has been repeatedly proven through clinical research. Comparisons with innovative methods such as mobile audiometry have shown that PTA still remains a reference point in terms of consistency and sensitivity. Furthermore, its ability to conduct a comprehensive evaluation over a wide range of frequencies allows for a detailed analysis of cochlear auditory sensitivity.

PTA provides consistent results across different clinical settings with standardized protocols, which is a great advantage in formulating effective treatment plans for patients. However, the test’s effectiveness also depends on the need for a soundproof environment and its reliance on the patient’s responses. For small children or individuals with cognitive difficulties, the subjective nature of the test may necessitate the use of additional methods.

Thanks to its strong diagnostic capacity and reliability, PTA continues to be an indispensable tool in hearing health evaluations. When considered alongside the innovations offered by other methods, it can provide a broader perspective for evaluation.

How Are Pure Tone Audiometry Results Interpreted?

Pure tone audiometry visualizes an individual’s hearing thresholds on a graphical audiogram, providing detailed information about the type, degree, and possible causes of hearing loss. The hearing thresholds displayed on the audiogram offer important clues in assessing hearing health.

The configuration of the hearing thresholds reflects different types of hearing loss. A flat configuration, where similar hearing loss is observed across all frequencies, typically indicates a conductive hearing loss related to outer or middle ear issues. A sloping configuration, characterized by poorer thresholds at high frequencies, is frequently seen in sensorineural hearing losses such as age-related hearing loss (presbyacusis). A rising configuration, which features poorer hearing at low frequencies and improved thresholds at high frequencies, supports the diagnosis of conditions such as hydrops/Ménière’s disease.

A notch configuration, which shows an abrupt drop at a specific frequency, is a more distinctive pattern, generally observed at high frequencies and is commonly encountered in noise-induced hearing loss. A U-shaped configuration (often referred to as a “cookie-bite” pattern), characterized by pronounced hearing loss in the mid frequencies, may be associated with genetic factors.

Interpreting audiogram results not only provides insight into the degree of hearing loss but also helps to understand the type of hearing loss and its possible underlying causes. This information plays a critical role in developing personalized treatment and rehabilitation strategies. Each configuration offers a roadmap for detailed evaluation and appropriate intervention.

It should always be kept in mind that these tests are performed in a sound-isolated environment with special stimuli. A mild degree of hearing loss identified in this environment may result in significant hearing and comprehension difficulties in noisy, real-life situations.

Dr. Ody. Emel Uğur

Dr. Audiologist Emel Uğur was born in 1982 in Çanakkale. She specialized in Pediatric Audiology, Otologic Disorders, and Vestibular System Disorders, and served for 15 years at the Istanbul Training and Research Hospital. In 2015, she joined the Acıbadem Healthcare Group. She currently works as an Audiologist at the Acıbadem Altunizade Hospital and also serves as a faculty member and program director in the Acıbadem University Vocational School of Health Services Audiometry Program.