[Histonet] Old control blocks

Morken, Timothy Timothy.Morken at ucsf.edu
Thu Oct 5 11:04:56 CDT 2017

Elaine, blocks last a very long time. The at the face the tissue may be oxidized, like a section on a slide, but the deeper tissue should be good. If you have several extra blocks just coat the face with paraffin to protect it.

However, the only way to be sure is to test them occasionally. If they are used regularly you can just note the last successful test (we keep a validation record of each block and note re-validation results on the form). If not used too often, test once a year to ensure it is good. Test the "extra paraffin-coated" blocks when  they are needed, not every year - maybe when the previous block is nearing its end test the next block in line to be sure you have a control available.

For the cryostat, for what part of the cryostat is the probe displaying a temperature?  It may not be the chamber temperature. Our cryostat display (and controls) are for the knife and object holder. There is no built-in display for the chamber. We did put in a manual-read thermometer for the chamber, and all show different temperatures.

The "correct" temperature is the one at which you get the best results!

Tim Morken
Pathology Site Manager, Parnassus 
Supervisor, Electron Microscopy/Neuromuscular Special Studies
Department of Pathology
UC San Francisco Medical Center

-----Original Message-----
From: Elaine allison Hoffman via Histonet [mailto:histonet at lists.utsouthwestern.edu] 
Sent: Thursday, October 05, 2017 8:42 AM
To: Histonetters Histonet
Subject: [Histonet] Old control blocks

 Hi everyone,
Just want to put a question out there. . . . 
How long can we keep control blocks (paraffin embedded tissue) before they go bad?  I just went through our old control blocks in our filing container and some of our control blocks have dates as far back as 10 years ago.  They have not been refrigerated or anything but didn't know if they should be thrown out and start over or how long they are good for?  They are filed in alphabetical order, anything from amyloid controls to yeast control blocks and many others in-between.  Or probably should be tested to see just how positive the staining results turn out to be.  I was just wondering if anyone knew off the top of their head, lol. Another brain teaser....
Our cryostat is displaying a temperature of -23 degrees but the thermometer sitting inside the chamber is reading -15 degrees.  The thermometer was just recently purchased and does not need calibrated or anything.  Our supervisor thought we should have a thermometer inside the cryo-chamber just to be certain that the digital display is accurate.  Now we have a dilemma!  Did anyone else experience this problem with the temperature readings with their cryostat?  Not really sure what to do about the different readings.  What should the correct temperature be anyways?
We would really appreciate any feed-back or suggestions.
Thank you,

Elaine Hoffman, HT(ASCP)
Steward Trumbull Memorial HospitalWarren, OH _______________________________________________
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