Histopath LAB Dehydration & Clearing

DEHYDRATION

  • Definition: Removal of intercellular and intracellular water from fixated/decalcified tissues before impregnation.
  • Process: Involves dehydrating agents, typically alcohol in varying concentrations:
    • Starts at 70% Ethanol in water.
    • Progresses through 95% Ethanol to 100% Ethanol.
    • Embryonic tissues start with 30% Ethanol.
  • Important Considerations: Keep exposure time brief to prevent loss of cellular constituents. Use at least 10 times the volume of the tissue in dehydrating agents.

DEHYDRATING AGENTS

Common Dehydrating Agents
  • Ethanol:
    • Preferred for routine dehydration; non-toxic and cost-effective.
  • Methanol:
    • Toxic; used for blood and tissue films.
  • Butyl Alcohol:
    • Suitable for plant and animal micro-techniques where rapid processing is not necessary.
Other Agents
  • Acetone:
    • Cheap and rapid; removes most lipids, not for routine use.
  • Dioxane (Diethyl Dioxide):
    • Excellent but highly toxic; tissues may not ribbon well when processed.
  • Cellosolve (Ethylene Glycol Monoethyl Ether):
    • Toxic effects on reproductive and fetal systems; safer alternatives exist.
  • Tetrahydrofuran:
    • Dehydrates and clears, miscible with various solvents; toxic when inhaled.

ADDITIVES TO DEHYDRATING AGENTS

  • 4% Phenol added to 95% Ethanol softens hard tissues (e.g., tendons, nails).
  • Glycerol/Alcohol mixtures can be used for hard tissues.

CLEARING

  • Definition: Removal of dehydrating agents from tissues (also called De-alcoholization).
  • Characteristics of Good Clearing Agents:
    • Miscible with alcohol for quick removal.
    • Compatible with paraffin for impregnation.
    • Minimized tissue shrinkage and damage.
    • Should not dissolve Aniline dyes.
Common Clearing Agents
  • Xylene:
    • Colorless, commonly used; ½ to 1 hour clearing time.
    • Not suitable for nervous tissues/lymph nodes.
  • Toluene:
    • Substitute for Xylene/Benzene; recommended time 1-2 hours.
  • Benzene:
    • For urgent biopsies; carcinogenic; rapid volatilization.
  • Chloroform:
    • Slower than Xylene; toxic with prolonged inhalation.
  • Cedarwood Oil:
    • Suitable for CNS studies; becomes milky over time.
  • Aniline Oil:
    • Recommended for delicate specimens; not routine.