Pure Tone Audiometry (AC, BC) at Dr. Essa Lab

Pure Tone Audiometry (AC, BC) at Dr. Essa Lab

Pure Tone Audiometry (AC, BC) is the gold standard behavioral diagnostic test used to evaluate an individual’s hearing sensitivity across a range of frequencies. This comprehensive assessment measures the quietest sounds a person can hear, establishing their hearing thresholds in decibels Hearing Level (dB HL). The test comprises two primary modalities: Air Conduction (AC) and Bone Conduction (BC). By comparing the results of these two pathways, clinical audiologists can precisely determine the type, severity, and configuration of hearing loss. Dr. Essa Laboratory & Diagnostic Centre, a trusted name in diagnostic excellence in Karachi, Pakistan, performs this test using advanced, calibrated audiometers within certified soundproof environments to ensure maximum clinical accuracy and reliability.

The auditory system is highly complex, consisting of the outer ear, middle ear, inner ear (cochlea), and the auditory nerve pathway leading to the brain. Air Conduction testing evaluates the entire auditory pathway. Sound waves travel through the air, enter the external auditory canal, vibrate the tympanic membrane (eardrum), pass through the middle ear ossicles (malleus, incus, and stapes), stimulate the fluid-filled cochlea, and finally send electrical signals via the vestibulocochlear nerve (cranial nerve VIII) to the temporal lobe of the brain. Bone Conduction testing, conversely, bypasses the outer and middle ear entirely. By placing a specialized bone vibrator on the mastoid process of the temporal bone, the skull is gently vibrated, directly stimulating the cochlea. This dual-pathway evaluation is clinically vital because it allows clinicians to isolate middle ear pathologies from inner ear or neural disorders.

The diagnostic value of Pure Tone Audiometry (AC, BC) lies in its ability to differentiate between the three main types of hearing loss: conductive, sensorineural, and mixed. Conductive hearing loss occurs when sound transmission is obstructed in the outer or middle ear, while bone conduction thresholds remain completely normal. Sensorineural hearing loss occurs when there is damage to the cochlea or the auditory nerve, resulting in equally elevated air and bone conduction thresholds. Mixed hearing loss presents as a combination of both, where both thresholds are abnormal, but an air-bone gap remains. This precise differentiation is crucial for ENT specialists, otologists, and general physicians to formulate appropriate medical, surgical, or rehabilitative treatment plans, such as prescribing hearing aids, middle ear surgery, or cochlear implants.

Clinical Procedure: What to Expect

Patient Preparation

To ensure highly accurate and reproducible results during your Pure Tone Audiometry (AC, BC) at Dr. Essa Lab, patients are advised to follow these preparation guidelines:

• Otoscopic Examination: Ensure your ears are examined by a healthcare professional prior to the test. Excess cerumen (earwax) must be professionally removed, as impacted wax can attenuate sound waves by up to 30 to 40 decibels, falsely indicating a conductive hearing loss.
• Avoid Loud Noise Exposure: Avoid exposure to loud noises, such as concerts, heavy machinery, firearms, or loud personal audio devices, for at least 12 to 16 hours before the test. This prevents a temporary threshold shift (TTS), which can temporarily degrade hearing thresholds.
• No Fasting Required: There are no dietary restrictions or fasting requirements. You may eat, drink, and take your routine medications as prescribed.
• Bring Medical Records: Bring any previous audiograms, ENT consultation notes, or history of ear surgeries to help the audiologist understand your clinical baseline.
• Report Current Symptoms: Inform the audiologist if you are currently experiencing active ear pain, discharge, dizziness, severe tinnitus, or if you currently have a cold or sinus congestion, as middle ear pressure changes can affect the test results.

During the Procedure

The Pure Tone Audiometry (AC, BC) procedure is entirely non-invasive, painless, and safe. Here is a detailed breakdown of what occurs during the evaluation:

• Soundproof Environment: The patient is seated comfortably inside a specialized, certified soundproof audiology booth designed to eliminate ambient environmental noise, which could otherwise interfere with the detection of very soft tones.
• Air Conduction Testing: The audiologist places calibrated over-ear headphones or insert earphones into the patient’s ear canals. The audiologist then presents pure tones at specific frequencies, typically ranging from 250 Hz (low pitch) to 8000 Hz (high pitch).
• Patient Response: The patient is instructed to press a hand-held response button, raise their hand, or verbally indicate “yes” every time they hear a tone, even if the sound is incredibly faint or barely audible.
• Bone Conduction Testing: A flexible headband with a small bone conduction transducer (vibrator) is placed behind the ear, resting firmly against the mastoid bone. Tones are presented again, directly stimulating the inner ear.
• Clinical Masking: If there is a significant difference in hearing sensitivity between the two ears, the audiologist may introduce a steady rushing sound (narrow-band noise) into the non-test ear. This process, called masking, prevents the better ear from “helping” the poorer ear, ensuring that each ear is evaluated independently.
• Duration: The entire test takes approximately 20 to 30 minutes. The patient experiences no discomfort, and there are no side effects or recovery times required.

When is a Pure Tone Audiometry (AC, BC) Performed?

1. Evaluation of Hearing Loss

Physicians request Pure Tone Audiometry when a patient reports progressive or sudden hearing loss, difficulty understanding speech in noisy environments, or a general feeling that sounds are muffled. The test establishes the exact degree of hearing loss, classified from mild to profound, helping to determine if the cause is a simple physical blockage or a complex sensory deficit.

2. Chronic Tinnitus Investigation

Persistent ringing, buzzing, roaring, or hissing in one or both ears—known as tinnitus—is frequently a symptom of underlying cochlear damage or hearing loss. Audiometry is performed to map out the patient’s hearing thresholds, as identifying specific frequency deficits can help target tinnitus management strategies, such as sound therapy or hearing aid programming.

3. Occupational Health Screening

Individuals working in high-noise environments, including aviation, construction, manufacturing, and military sectors, are at high risk for noise-induced hearing loss. Routine audiometric monitoring is performed to detect early signs of cochlear damage, typically characterized by a “notch” in hearing sensitivity around 4000 Hz, allowing for timely intervention and hearing conservation measures.

4. Ototoxic Medication Monitoring

Certain lifesaving medications, including specific chemotherapy agents (such as cisplatin), aminoglycoside antibiotics (such as gentamicin), and high-dose loop diuretics, are known to be ototoxic, meaning they can permanently damage the hair cells of the cochlea. Baseline and serial audiometry tests are performed to monitor hearing function, allowing oncologists or physicians to adjust drug dosages if early hearing loss is detected.

5. Post-Infection or Trauma Assessment

Patients who have suffered head trauma, temporal bone fractures, blast injuries, or chronic middle ear infections (such as chronic suppurative otitis media) require audiometric evaluation. The test helps assess whether the trauma or infection has caused structural damage to the middle ear ossicles (conductive loss) or permanent damage to the inner ear structures (sensorineural loss).

What Does a Pure Tone Audiometry (AC, BC) Detect?

Pure Tone Audiometry (AC, BC) is highly sensitive and can detect a wide range of clinical conditions and auditory pathologies, including:

• Normal Hearing Sensitivity: Thresholds across all tested frequencies remain between -10 dB HL and 25 dB HL.
• Conductive Hearing Loss: Elevated air conduction thresholds with completely normal bone conduction thresholds, indicating outer or middle ear pathology.
• Sensorineural Hearing Loss: Equally elevated air and bone conduction thresholds, indicating cochlear or vestibulocochlear nerve damage.
• Mixed Hearing Loss: Elevation in both air and bone conduction thresholds, with an air-bone gap greater than 10 dB, indicating pathology in both the conductive and sensory systems.
• Presbycusis: Age-related, bilateral, symmetrical high-frequency sensorineural hearing loss.
• Noise-Induced Hearing Loss (NIHL): A characteristic diagnostic notch or drop in thresholds at 4000 Hz, with recovery at 8000 Hz.
• Otosclerosis: A middle ear bone disease indicated by a specific drop in bone conduction thresholds at 2000 Hz, known as Carhart’s notch.
• Tympanic Membrane Perforation: Conductive hearing loss resulting from a tear or hole in the eardrum.
• Ossicular Chain Discontinuity: A separation of the middle ear bones, often due to trauma, causing a significant conductive hearing loss.
• Ossicular Fixation: Stiffness of the middle ear bones, restricting sound transmission.
• Eustachian Tube Dysfunction: Mild conductive hearing loss caused by chronic negative pressure in the middle ear cavity.
• Meniere’s Disease: Fluctuating, low-frequency sensorineural hearing loss, typically unilateral in early stages, accompanied by vertigo and tinnitus.
• Acoustic Neuroma (Vestibular Schwannoma): Unilateral or highly asymmetrical high-frequency sensorineural hearing loss, indicating a benign tumor on the auditory nerve.
• Ototoxicity: Progressive, bilateral high-frequency sensorineural hearing loss caused by drug exposure.
• Barotrauma: Conductive or sensorineural damage resulting from rapid atmospheric pressure changes, such as during scuba diving or flights.
• Chronic Suppurative Otitis Media (CSOM): Persistent middle ear infection causing conductive hearing loss due to fluid or ossicular damage.
• Cerumen Impaction: Temporary conductive hearing loss caused by a complete blockage of the external auditory canal.
• Otitis Media with Effusion (Glue Ear): Conductive hearing loss due to fluid accumulation behind an intact eardrum.
• Congenital Hearing Loss: Hereditary or prenatal hearing deficits, often presenting with a “cookie-bite” audiogram configuration.
• Acoustic Trauma: Sudden sensorineural hearing loss resulting from exposure to an intense blast or explosion.
• Sudden Sensorineural Hearing Loss (SSNHL): An idiopathic, rapid loss of hearing in one ear within a 72-hour window, requiring urgent medical evaluation.
• Auditory Neuropathy Spectrum Disorder (ANSD): Normal or near-normal cochlear function but abnormal neural transmission, requiring further specialized testing.
• Unilateral Hearing Loss: Hearing impairment isolated to one ear, indicating localized pathology.
• Bilateral Symmetrical Hearing Loss: Equal hearing loss in both ears, typical of systemic, genetic, or age-related causes.
• Bilateral Asymmetrical Hearing Loss: Unequal hearing loss between ears, necessitating further imaging to rule out retrocochlear lesions.

Turnaround Time and Report Access at Dr. Essa Lab

At Dr. Essa Laboratory & Diagnostic Centre, we understand the importance of timely diagnostic results. The Pure Tone Audiometry (AC, BC) test is performed by qualified audiologists, and the raw audiogram data is plotted immediately during the session. A comprehensive, formal diagnostic report, complete with the audiogram graph, threshold values, and clinical interpretation, is typically compiled and verified within a few hours of the test completion. Patients can conveniently access and download their digital reports online through the secure Dr. Essa Lab web portal or mobile application. Printed copies of the reports can also be collected directly from the reception desk of the respective Karachi branch where the test was conducted.

Pure Tone Audiometry (AC, BC) Findings Overview

Structure / Parameter Evaluated	Normal Findings	Possible Abnormal Findings
Air Conduction (AC) Thresholds	Thresholds between -10 dB HL and 25 dB HL across all frequencies (250 Hz to 8000 Hz).	Thresholds > 25 dB HL, indicating mild, moderate, severe, or profound hearing loss.
Bone Conduction (BC) Thresholds	Thresholds between -10 dB HL and 25 dB HL, closely matching AC thresholds.	Thresholds > 25 dB HL, indicating sensorineural or mixed hearing loss.
Air-Bone Gap (ABG)	Difference between AC and BC thresholds is 10 dB or less.	Difference > 10 dB, indicating a conductive hearing loss component.
High-Frequency Sensitivity (4-8 kHz)	Thresholds within normal limits (≤ 25 dB HL).	Sloping thresholds > 25 dB HL, suggesting presbycusis, noise damage, or ototoxicity.
Low-Frequency Sensitivity (250-500 Hz)	Thresholds within normal limits (≤ 25 dB HL).	Elevated thresholds, commonly seen in early Meniere’s disease or Eustachian tube dysfunction.
Interaural Symmetry	Symmetrical thresholds between the left and right ears (difference < 15 dB).	Asymmetrical thresholds (difference ≥ 15 dB), suggesting unilateral pathology like acoustic neuroma.
Audiogram Configuration	Flat configuration with all thresholds within normal limits.	Notched (noise-induced), cookie-bite (congenital), or sloping (presbycusis) configurations.

Note: Diagnostic findings should always be interpreted by a qualified healthcare professional together with the patient’s symptoms, medical history, physical examination, laboratory investigations, previous imaging studies, and other relevant clinical information. Additional investigations or specialist consultation may be recommended depending on the findings.

Why Choose Dr. Essa Lab for Pure Tone Audiometry (AC, BC)?

• Experienced Healthcare Professionals: Our audiology department is staffed by highly trained, qualified clinical audiologists with extensive experience in pediatric and adult hearing assessments.
• Patient-Focused Care: We prioritize patient comfort, safety, and clear communication, ensuring a stress-free testing experience for individuals of all ages.
• Quality Diagnostic Services: Dr. Essa Lab is committed to clinical excellence, utilizing standardized protocols to deliver highly accurate and reproducible diagnostic results.
• Professional Reporting: All audiograms are meticulously interpreted, verified, and presented in a clear, easy-to-understand format for both patients and referring physicians.
• Modern Diagnostic Approach: We utilize state-of-the-art diagnostic audiometers and certified soundproof booths that comply with international standards for ambient noise levels.
• Comfortable Environment: Our diagnostic facilities are designed to provide a clean, quiet, and welcoming atmosphere for all patients.
• Convenient Location: With an extensive network of branches across Karachi, Pakistan, patients can easily access our audiology services close to home.
• Commitment to Accurate Diagnosis: Since 1987, Dr. Essa Lab has maintained a legacy of trust, accuracy, and dedication to the healthcare needs of the community.