Following are the properties of ideal fixatives (buffered formalin)

Properties of an ideal fixative in histopathology

  • An ideal fixative prevents autolysis and bacterial decomposition in the tissue.
  • It preserves the tissue in its natural state.
  • Fix all tissue components at their position.
  • Makes the cellular component insoluble to the reagent used in tissue processing
  • Preserve the tissue volume.
  • Avoid excessive hardness of tissue.
  • Enhance tissue staining(H and E stain) process.
  • It should be non-toxic and non-allergic to the user.
  • Good fixative should be cheap.

Classification of chemical fixatives in the Histopathology laboratory

Fixatives are classified into three groups.

  1. Tissue fixatives
  2. Histochemical fixatives
  3. Cytology fixatives

What are the tissue fixatives examples? 

These fixatives are specially used for tissue fixation. Following fixatives used for tissue

  • Buffered Formal saline
  • Zenker Solution
  • Buffered Glutaraldehyde

What are Histochemical fixatives names?

These fixatives are specially used for histochemical fixation. Following fixatives used

  • Cold acetone
  • Absolute Alcohol
  • Formal Saline

What are the Cytological fixatives and examples?

These fixatives are used for cytological specimens. Following fixatives used in the cytology

  • Ether
  • Methanol
  • Ethanol

What are the 10 most common types of fixative used in Histopathology?

Two fixatives are commonly used

    1. 10% Routine Formalin
    2. 10% Buffered Formalin
    3. Ethyl Alcohol
    4. Mercuric Chloride
    5. Picric Acid
    6. Chromic Acid
    7. Potassium Dichromate
    8. Osmic Acid (Osmium Tetra Oxide)
    9. B-5 Fixative
    10. Zinker Solution

5 Properties of 10% routine formalin histopathology

  • It is prepared by  40% w/w solution of formaldehyde gas in water.
  • Routine formalin used 10% or 15%  V/V in normal saline or calcium chloride solution.
  • It does not precipitate PROTEIN. But combine with NH2 to form an insoluble gel.
  • Preserves all components including fats. Phospholipid insoluble in fat solvents.
  • Cheapest and most popular fixative in histology.

What is the disadvantage of 10% routine formalin?

Routine formalin has acidic PH. This results in haematin crystal formation during fixation. These crystals also affect tissue staining(Hematoxylin and eosin).

10% neutral buffered formalin composition

  1. Normal saline  100 ml
  2. Pure formalin    10  ml
  3. Sodium dihydrogen phosphate  0.4 g
  4. Disodium hydrogen phosphate  0.65 g

Note: 10% buffered formalin prepared after mixing all these substances.

6 Advantages of 10% neutral buffered formalin

Following are the uses or advantages of 10 percent neutral buffer

  • Tissue can be preserved in it for a longer time.
  • There is no hardening of the tissue.
  • Tissue sectioning is easy.
  • No haematin crystal is formed.
  • It enhances tissue staining.
  • A number of stains can be used of such preserved tissue.

Fixative of choice and Target table (Do, don’t)

Following fixatives are used as a fixative of choice for protein, lipid, enzyme.

Fixative of choice Target To be avoided
Frozen section Enzyme Chemical fixative
Buffered formalin Protein Osmium tetraoxide
Alcohol fixative Nucleic acid Aldehyde Fixative
Alcohol-based fixative Glycogen Osmium tetraoxide
Frozen section Lipid Alcohol, formalin
Frozen Section Mucopolysaccharide Chemical Fixative
     
  1. Why do we use 10% neutral buffered formalin in histology?

    Routine formalin cause crystal formation due to acidic PH. Therefore neutral PH is necessary for better results. For this purpose, PHOSPHATE BUFFER is added in 10% buffered formalin.

  2. How to prepare 10% neutral buffered formalin?

    10% neutral buffered formalin prepared by mixing 10 ml pure formalin with 100 ml normal saline. We also use phosphate which prevents crystal formation.

  3. What is the fixative of choice for protein, enzyme study?

    The frozen section is used as a fixative for enzyme study, while buffered formalin is the fixative of choice for protein preservation.

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what is the difference between antiseptic and disinfectant? How to collection and handle cytology specimen
what is the difference between antiseptic and disinfectant? How to collection and handle cytology specimen