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Cytogenetics

Biological Hazard

Cytogenetics laboratories handle fresh, viable human tissue, including peripheral blood, bone marrow, amniotic fluid, chorionic villi, and solid tumor biopsies. Unlike clinical chemistry or hematology where samples are often analyzed in closed automated systems, cytogenetics involves extensive manual manipulation of open specimens (e.g., culturing, harvesting, and slide dropping). This increases the risk of exposure to bloodborne pathogens (HIV, Hepatitis B/C). Therefore, adherence to Standard Precautions and rigorous decontamination protocols is mandatory

Standard Precautions (Universal Precautions)

The fundamental rule of laboratory safety, mandated by OSHA, is to treat all human blood, body fluids, and tissues as if they are known to be infectious for HIV, HBV, and other bloodborne pathogens

  • Scope: Applies to all clinical specimens received in the cytogenetics lab
  • Engineering Controls: Using equipment (like centrifuges with sealed buckets) to isolate the hazard from the worker
  • Work Practice Controls: Changing behaviors to reduce risk (e.g., no mouth pipetting, no eating/drinking in the lab, washing hands immediately after removing gloves)

Personal Protective Equipment (PPE)

PPE acts as the last line of defense between the laboratory scientist and the biological hazard. It must be donned before entering the technical area and removed before leaving

  • Gloves
    • Requirement: Must be worn for all specimen handling steps (receipt, set-up, harvest, slide making)
    • Material: Nitrile is preferred over latex due to allergy risks and better chemical resistance
    • Protocol: Change gloves immediately if contaminated or torn. Never touch “clean” surfaces (doorknobs, phones, keyboards) with “dirty” gloves
  • Laboratory Coats
    • Requirement: Fluid-resistant, long-sleeved, and knee-length
    • Usage: Must be buttoned/snapped completely to protect street clothes
    • Laundering: Contaminated coats must be laundered by the facility or a professional service; they must never be taken home
  • Face and Eye Protection
    • Requirement: Necessary whenever there is a risk of splashing or aerosolization
    • Cytogenetics Context: Essential during the “dropping” phase of slide preparation if done on an open bench, and during the aspiration of supernatant during harvest. Face shields or safety goggles with side shields are standard
  • Footwear
    • Closed-toe shoes with non-porous uppers (leather or rubber, not mesh) are required to protect against dropped scalpels or spilled fluids

The Biological Safety Cabinet (BSC)

The BSC is the primary containment device used during cell culture set-up. Cytogenetics labs typically use Class II, Type A2 cabinets

  • Protection Triad
    1. Personnel: Inward airflow protects the user from the specimen
    2. Product: HEPA-filtered downward air protects the cell culture from bacterial/fungal contamination
    3. Environment: Exhaust air is HEPA-filtered before re-entering the room or building exhaust
  • Operational Best Practices
    • Sash Height: Maintain the sash at the certified level (usually marked). Raising it too high disrupts airflow and triggers an alarm
    • Air Grilles: Never block the front or rear air intake grilles with notebooks, pipette tip boxes, or arms. This creates turbulence and breaks the containment barrier
    • Movement: Move arms slowly (“swim”) in and out of the cabinet to prevent drag-out of aerosols
    • Clean-to-Dirty: Organize the workspace so that clean media is on one side, the specimen in the center, and waste on the other side. This prevents passing dirty pipettes over clean flasks

Decontamination of Surfaces & Equipment

Decontamination renders an item or surface safe to handle. The choice of agent depends on the target (biological vs. chemical) and the surface material

  • Disinfectants
    • 10% Sodium Hypochlorite (Bleach): The most effective broad-spectrum disinfectant (kills HIV, HBV)
      • Usage: Used for large blood spills and liquid waste treatment
      • Caution: Corrosive to stainless steel (BSC interiors). If used in a hood, it must be followed by a water or alcohol rinse
    • 70% Ethanol or Isopropanol
      • Usage: Routine cleaning of BSC work surfaces, pipettes, and benchtops
      • Mechanism: Denatures proteins and dissolves lipids. Effective against vegetative bacteria but less effective against spores than bleach
  • Routine Schedules
    • Daily: Bench tops and BSC surfaces must be wiped down with 70% ethanol at the start and end of every shift, and immediately after any overt spill
    • Weekly/Monthly: Water baths (incubators and warming baths) must be drained and cleaned with a phenolic detergent or 10% bleach (rinsed thoroughly) to prevent Pseudomonas or fungal blooms
    • Centrifuges: If a tube breaks during harvest, the bucket and rotor must be autoclaved or soaked in non-corrosive disinfectant

Biological Spill Management

When a specimen tube breaks or culture media is spilled, immediate action is required

  1. Alert: Warn others in the area
  2. PPE: Ensure gloves, coat, and eye protection are on
  3. Contain: Place absorbent material (paper towels) over the spill to stop it from spreading
  4. Disinfect: Pour 10% Bleach over the paper towels (gently, to avoid splash). Allow 20 minutes of contact time
  5. Cleanup: Remove towels with forceps or gloved hands. Dispose of in Biohazard Waste
  6. Final Wipe: Clean the area with water (to remove bleach residue) and then alcohol
  7. Glass: If broken glass is involved, never pick it up with hands. Use a brush and dustpan or forceps

Waste Disposal

Proper segregation of waste is critical for safety and environmental compliance

  • Sharps Containers (Red/Rigid)
    • Used for: Microscope slides (glass), Pasteur pipettes (glass), needles, and scalpels used for tissue mincing
    • Rule: Never recap needles. Do not overfill containers (stop at the fill line)
  • Biohazard Bags (Red)
    • Used for: Soft items contaminated with blood/fluids (gloves, plastic pipettes, flasks, Kimwipes)
  • Liquid Waste
    • Culture media and harvest supernatants (which contain human cells) are often treated with bleach (final concentration 10%) for 30 minutes before being poured down the drain (subject to local wastewater regulations)