Specimen Fixation

Immediate fixation of cellular material is essential for accurate diagnoses and it cannot be overemphasized.  The cytologic fixative maintains the morphologic characteristics of the cells as closely as possible to their natural state.  The fixative should penetrate rapidly, minimize cell shrinkage, maintain morphologic integrity, prevent putrefaction from molds and bacteria and inactivate autolytic enzymes that would cause autolysis.  Proper fixation also allows permeability of dyes across cell boundaries, enhances cell adhesion to the glass slide and enables a permanent cellular record.  Since cytologic fixatives are alcohol based, they also act as a dehydrating agent, replacing the water within the cell.

 

According to CLIA, approximately 40% of all Pap smear false negative errors can be attributed to improper collection.  For satisfactory results, collected cells should be smeared on slides in a thin, even layer or prepared for thin prep and than fixed immediately before the cells dry.  The recommendation from CLIA is either 30 minutes in 95% ethyl or reagent alcohol (80% isopropanol may be substituted) or a commercial spray fixative which is normally a mixture of alcohol and a waxy substance (carbowax).  Body fluids for cell block should be prepared immediately upon receipt or refrigerated.

 

Saccomanno Collection Fluid (CAT# SL25) is a premixed, ready to use fixative that is recommended for sputum collection.  Red blood cells are lysed and mucoproteins remain suspended.  Cells from samples are easily concentrated by centrifuging or filtering and they exhibit excellent staining characteristics.  It is available in 16 oz or 1 gallon bottles and 2 ½ gallon cubitainers.  It also comes in convenient prefilled 120ml polypropylene collection containers (40ml of Saccomanno fluid).

 

Carbofix™ (CAT# CF100), prepared for the preservation of cytology smears, is a solution of isopropyl alcohol with polyethylene glycol in a convenient non-aerosol pump spray bottle.  Each 4 ounce bottle will fix approximately 700 slides.  It is available in cases containing 12 bottles.

 

95% Reagent Alcohol (CAT# 9500) complies with the CLIA recommendations for cytology fixatives.  It is available in 1 gallon bottles with 4 bottles per case.

 

Isopropyl Alcohol (CAT# 36420) is a 99% solution that can be easily diluted to the CLIA recommended 80% solution.  It is available in 1 gallon bottles with 4 bottles per case.