Pure Tone Audiometry Explained: What the Test Involves
Pure tone audiometry is one of the most widely used methods for evaluating hearing. It provides a clear and measurable way to determine how well a person can detect sounds across different pitches and volumes. Because hearing loss often develops gradually, this test plays an important role in early detection and diagnosis.
What Is Pure Tone Audiometry?
Pure tone audiometry is a behavioral hearing test that aims to measure the softest sounds a person can hear. These sounds, called pure tones, are single-frequency signals presented through headphones or other transducers. The goal is to determine the hearing threshold at each frequency tested.
The test typically covers frequencies from 250 Hz to 8,000 Hz, which includes the range most important for understanding speech. By testing across this range, audiologists can identify patterns of hearing loss that may affect communication in everyday situations.
This test is commonly used in the following, among others:
- Routine hearing evaluations
- Occupational health screenings
- Diagnostic assessments
How the Test Works
The test is usually conducted in a quiet or sound-treated environment to minimize background noise. The patient wears headphones or insert earphones, and the audiologist presents tones at different frequencies and intensity levels.
Each time the patient hears a sound, they respond using a pre-agreed method, such as pressing a button or raising a hand. This method is called air conduction testing. The audiologist adjusts the loudness of the tones to find the softest level the patient can detect. This is done using a standard approach, often referred to as the “down 10 dB, up 5 dB” method. The process is repeated across multiple frequencies to establish a full hearing profile.
In addition to air conduction testing, bone conduction testing may also be performed. A small device placed behind the ear sends vibrations directly to the inner ear, bypassing the outer and middle ear. Comparing these two methods helps determine whether hearing loss is conductive or sensorineural, or mixed. The test is non-invasive and usually takes about 20 to 30 minutes to complete.
What PTA Measures
Pure tone audiometry (PTA) measures hearing thresholds, which refer to the softest sounds a person can detect at specific frequencies. These thresholds are recorded in decibels hearing level (dB HL) and provide a clear, standardized way to assess hearing sensitivity.
The test focuses on frequencies that are critical for speech understanding, typically between 500 Hz and 4,000 Hz, while also including lower and higher frequencies for a complete profile. By measuring across this range, PTA helps identify which parts of the sound spectrum are affected and how that may impact everyday communication.
PTA also measures hearing in each ear separately. This allows clinicians to detect asymmetry, where one ear performs differently from the other. Differences between ears can be clinically significant and may require further investigation.
Another key aspect of PTA is the comparison between air conduction and bone conduction thresholds. This comparison helps determine where the hearing issue is located within the auditory system. For example, if sound transmission through air conduction is reduced but bone conduction remains within normal limits, the issue may involve the outer or middle ear. If both are reduced at similar levels, the problem is more likely related to the inner ear or auditory nerve.
In addition to identifying hearing thresholds, PTA helps classify the degree of hearing loss. Hearing levels are generally categorized as:
- Normal: 0–25 dB HL
- Mild: 26–40 dB HL
- Moderate: 41–55 dB HL
- Moderately severe: 56–70 dB HL
- Severe: 71–90 dB HL
- Profound: 91 dB HL and above
These categories help guide clinical decisions, including whether intervention such as hearing aids or medical treatment may be needed.
Understanding Results
The results of pure tone audiometry are presented on an audiogram, which provides a visual summary of hearing thresholds across frequencies. Frequencies (pitch) are shown along the horizontal axis, while intensity (loudness) is shown on the vertical axis.
Each ear is plotted separately using standard symbols, allowing clinicians to compare hearing levels side by side. The pattern or shape of the audiogram often provides important diagnostic clues. For example, a gradual slope at higher frequencies is commonly associated with age-related or noise-induced hearing loss, while a flat pattern may suggest a different underlying issue.
Audiologists also look for the presence of an air-bone gap, which is the difference between air conduction and bone conduction thresholds. This gap helps identify whether a hearing problem is conductive in nature. If no significant gap exists and thresholds are elevated, the hearing loss is more likely sensorineural.
Consistency is another important factor when interpreting results. Audiologists may repeat certain frequencies, such as 1,000 Hz, to confirm reliability. If responses are inconsistent, the results may need to be interpreted with caution or repeated.
PTA results are rarely viewed in isolation. They are often combined with other assessments, such as speech audiometry or tympanometry, to build a more complete picture of hearing health.
Conclusion
Pure tone audiometry provides a clear and structured way to evaluate hearing. It measures how well a person detects sound across different frequencies and intensities, offering detailed insight into hearing ability.
If you’ve noticed changes in your hearing, consider addressing them early. Our Toronto audiologists provide a range of hearing services to assess your needs and discuss care options that align with your lifestyle and budget.