High-Level Disinfection (HLD)

High-level disinfection (HLD) eliminates all microorganisms — bacteria, viruses, fungi, and mycobacteria — except high numbers of bacterial spores. It is the minimum reprocessing requirement for semi-critical items (devices that contact mucous membranes or non-intact skin but do not enter sterile tissue).

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Common HLD Agents

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Manual HLD Process

Step-by-Step:

1. Clean the device thoroughly — HLD will not be effective on items with remaining soil
2. Test the solution with MEC test strips to verify the chemical concentration is at or above the Minimum Effective Concentration
3. Completely immerse the device in the HLD solution — all channels and lumens must be filled
4. Maintain immersion for the manufacturer-specified contact time at the specified temperature
5. Rinse thoroughly with sterile water, filtered water, or tap water (depending on device use) to remove all chemical residue
6. Dry the device — use forced air or alcohol rinse followed by air drying per manufacturer IFU
7. Document the processing: date, time, chemical used, contact time, MEC verification, technician initials

Critical Points:

• MEC (Minimum Effective Concentration) — Test with appropriate test strips before EACH use (not just daily)
• If MEC is below the minimum, discard the solution and prepare fresh
• Complete immersion is required — air bubbles trapped in lumens prevent chemical contact
• Never shorten the contact time — the full manufacturer-specified time is required for efficacy
• Rinsing is critical — chemical residue can cause chemical burns to mucous membranes

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Automated Endoscope Reprocessors (AERs)

AERs automate the HLD process for flexible endoscopes, providing more consistent and reproducible results than manual processing:

Advantages over manual HLD:

• Standardized cycle parameters (temperature, time, concentration)
• Automated channel flushing ensures chemical reaches all internal surfaces
• Built-in rinse cycles ensure thorough chemical removal
• Electronic documentation and cycle records
• Reduced chemical exposure to technicians

AER Process:

1. Manual precleaning at point of use (still required)
2. Leak testing
3. Manual cleaning (brushing all channels)
4. Place in AER — connect all channel adapters
5. AER runs automated wash, HLD, rinse, and (sometimes) alcohol flush cycles
6. Remove and dry or store per IFU

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Safety Requirements for HLD Chemicals

• PPE required: Chemical-resistant gloves, face shield/goggles, fluid-resistant gown
• Ventilation: Work under fume hood or in well-ventilated area; monitor vapor levels
• Exposure limits: Follow OSHA PEL (Permissible Exposure Limit) for each chemical
  • Glutaraldehyde: 0.05 ppm ceiling (NIOSH REL)
  • OPA: No established OSHA PEL, but minimize exposure
• Spill response: Know spill kit locations and neutralization procedures
• SDS: Maintain current Safety Data Sheets for all HLD chemicals