When a surgical team needs a fast turnaround time from the pathologist on a fresh tissue, the lab professionals turn to frozen sectioning and the cryostat.

Cryostat sectioning introduces a few more potential hazards as well as being a bit more challenging. The problems encountered with sectioning frozen samples are often different than the potential issues from handling paraffin-embedded tissues.

And there’s a good chance that the surgical team is standing by with a patient, who likely remains under anesthesia until the pathology results are received. The report from the pathologist will direct the course of action in the operating room… the patient’s life may hang on getting the right diagnosis.

Still, histo techs need to work quickly, carefully, and effectively while protecting the health and safety of themselves and everyone in the lab.

Cryostat Operation – Precautions

Working with the cryostat and sectioning frozen samples bears many similarities to microtome sectioning, but handling tissues at -20°C to -40°C requires an added level of caution. The main safety considerations when using the cryostat are the potential for infectious agents being aerosolized, frostbite or injury from handling frozen items, injury from sharp blades, and ergonomics. We’ll take a closer look at these below.

 Infectious samples

 Tissue samples may contain infectious agents. Samples from patients who are or may be positive for certain diseases require special handling. Some such diseases are:

  • HIV
  • Hepatitis B or C
  • Tuberculosis
  • Prion diseases
  • Mycobacterial diseases
  • Systemic fungal diseases
  • SARS-related diseases[1]

This is not a guaranteed complete list… always verify the potential of infectious agents before handling samples and follow your lab’s best practices for handling potential airborne pathogens.

 Use of rapid freeze sprays is not recommended when the presence of any of these pathogens is present or suspected. Using sprays on fresh tissue samples can aerosolize infectious pathogens that may be on the sample.

 After sectioning tissues carrying (or potentially carrying) any of the above, the cryostat must also be decontaminated in order to minimize risks. 


 With temperatures as low as -50°C, bare skin can suffer frostbite in an instant. Follow these tips to help prevent injury from the freezing temperatures:

  • Always take care to keep skin from making direct contact with metal parts (even if you’re triple-dog dared).
  • Wear utility gloves when handling frozen materials or working with chemicals used for quick freezing.
  • Always remove forceps and other utensils from the cryostat when they aren’t being used. They should, however, be placed in the cryostat chamber before use so they won’t warm the sample as you work. Specimen chucks should remain at room temperature until it’s time to mount the tissue.

Sharp blades

 Even a dull cryostat or microtome blade can yield quite a cut. Some blade-handling musts:

  • Never handle a blade with bare hands… use forceps or wire mesh or cut-resistant gloves when removing or inserting blades.
  • Keep the blade lock on when the blade is on the holder.
  • Use a blade guard when it’s not in use.
  • Lock the arm/wheel when it’s not being used.
  • Never remove the blade holder containing a blade from the cryostat.


 Repetitive motion injuries, pain, and discomfort due to posture and positioning can be reduced or eliminated by following some simple ergonomic practices. These are essentially the same as they would be with a microtome:

  • Use an adjustable chair, bench, and/or footrest to allow for straight posture.
  • Put padding on the edge where the forearm rests.
  • Adjust chair or equipment height so that the operator’s arm can be kept close to the body with a straight wrist when turning the handwheel.
  • Use an automatic foot-operated cryostat if possible.

 To learn more about ergonomics throughout the lab, check out this article.

 Always follow your company or lab’s best practices or safety rules and remember it’s better to err on the side of caution when it comes to protecting health and safety.

Are Quick or Rapid Freeze Sprays Safe to Use?

When tissue is being frozen, it needs to be frozen quickly. This is not just because of time constraints, but because slow freezing can result in damaged tissue samples. If it is allowed to freeze slowly, there’s a chance of ice crystals forming inside the tissue. Quick freezing prevents the water from crystallizing and expanding, preserving the tissue without artefacts.

Freeze sprays such as Azer Scientific’s Rapid Freeze Spray offer a quick and convenient way to rapidly cool tissue for sectioning. Quick freezing sprays are safe when used correctly and according to the product’s label.

 Some important rules with regard to use of rapid freeze sprays are:

  • Not all available sprays are non-flammable. Never use a flammable spray in or near a cryostat. Flammable freezing sprays can ignite potentially causing serious injuries. Elimination of flammable freeze sprays from the lab will help reduce the risk of inadvertent use. If for some reason they can’t be eliminated, be sure they are clearly marked and stored in a separation location away from the non-flammable sprays like Azer’s Rapid Freeze Spray.
  • Do not use spray on fresh tissues containing possible airborne pathogens. Use of sprays on fresh tissue samples can aerosolize infectious pathogens that may be on the sample. Review the list of potential infectious agents above.

 Note: On June 4, 2019, there was a recall issued by Leica Biosystems regarding some of their cryostats. The recalled devices were missing a label warning of the potential fire danger with use of flammable freezing sprays.[2]

 Azer Scientific’s Rapid Freeze Spray is a non-flammable, moisture-free alternative to flammable sprays, and it can reduce sample temperature to -51°C in just three seconds. Rapid Freeze Spray doesn’t contain chlorofluorocarbons (CFCs) or hydrofluorocarbons (HFCs) so it’s ozone safe.

 PathSUPPLY can ship your Rapid Freeze Spray (Item ID: RAP-FRZ), the same day you order when the order is placed by 2 pm Eastern.

 Get your Rapid Freeze Spray, specimen chucks, or other cryostat or lab needs at PathSUPPLY. Reach out to your sales rep or our customer service team at 800-631-3556 if there’s anything we can help you with.

 At PathSUPPLY we’re helping those who help patients.

[1] Gross Pathology, Izak B. Dimenstein, MD, PHD, HT (ASCP), Prevention of infection exposure during frozen section

[2] U.S. Food and Drug Administration, Class 2 Device Recall Leica Cryostats, June 4, 2019