Pure Tone Audiometry

Overview

Pure tone audiometry (PTA) is the gold standard for determining hearing thresholds across frequencies. This protocol establishes standards for conducting air and bone conduction testing.

Equipment Requirements

• Calibrated two-channel audiometer
• Sound-treated test environment meeting ANSI S3.1-1999 standards
• Air conduction headphones/inserts
• Bone conduction oscillator
• Patient response button
• Masking noise capability

Pre-Test Procedures

1. Environment Check
   • Ambient noise levels within ANSI specifications
   • Equipment daily calibration verification
   • Patient positioning at 90-degree angle to examiner
2. Patient Preparation
   • Remove hearing aids, glasses, masks interfering with headphone placement
   • Clear instructions on:
     • Raising hand/pressing button when tone is heard
     • Responding to very faint sounds
     • Importance of consistency

Testing Protocol

Air Conduction

1. Initial Presentation
   • Begin at 1000 Hz at 50 dB HL
   • If no response, increase in 10 dB steps
   • If response, proceed with threshold search
2. Threshold Determination
   • Use modified Hughson-Westlake procedure:
     • Decrease in 10 dB steps until no response
     • Increase in 5 dB steps until response
     • Threshold = lowest level with 2/3 responses
3. Frequency Sequence
   • 1000 Hz (retest for reliability)
   • 2000 Hz
   • 4000 Hz
   • 8000 Hz
   • 500 Hz
   • 250 Hz
   • 3000 Hz, 6000 Hz as needed

Bone Conduction

1. Oscillator Placement
   • Position on mastoid process
   • Consistent pressure (400-600 grams)
   • Clear hair from contact area
2. Testing Sequence
   • Test frequencies: 500-4000 Hz
   • Use same threshold search procedure
   • Consider masking needs

Masking Protocol

1. Air Conduction
   • Initial mask when interaural attenuation exceeded:
     • 40 dB for supra-aural phones
     • 55 dB for insert phones
   • Plateau method for determining masked threshold
2. Bone Conduction
   • Always mask contralateral ear
   • Starting level = AC threshold + 10 dB
   • Increase masking until plateau reached

Documentation

• Mark thresholds using standard symbols:
  • Right AC: Red O
  • Left AC: Blue X
  • Right BC: < in red
  • Left BC: > in blue
  • Masked: Symbol filled
• Note reliability indicators
• Document modifications to standard protocol
• Record test conditions and equipment

Quality Control

• Perform listening check daily
• Document ambient noise levels
• Regular calibration schedule
• Cross-check with speech thresholds

Special Considerations

1. Pediatric Modifications
   • Conditioned play audiometry
   • Visual reinforcement
   • Shorter test sequences
2. Difficult-to-Test Patients
   • Modified response methods
   • Increased time allowance
   • Alternative test strategies

References

• ANSI S3.21-2004 Methods for Manual Pure-Tone Threshold Audiometry
• ASHA Guidelines for Manual Pure-Tone Threshold Audiometry