Pre-fixation versus post-fixation: what’s the difference?

Pre-fixation versus post-fixation. Sounds complicated. What do those terms mean, anyway?

Pre-fixation: The pre-fixation time is from drawing blood to putting it into our first buffer “stable lyse,” starting the blood fixation process. This stage needs to be done within five hours from the time of blood draw.

(The time between adding Buffer 1 and adding Buffer 2 is the “fixation time” which is a separate measurement that should be the recommended 15 min. At this point, the sample is “fixed”: meaning the cells have been “snapshotted” in place.)

Drug developers care about this measure because it can tell them how long a phlebotomist has to put the blood sample into a collection kit. A five hour window gives drug developers the flexibility to collect blood samples from multiple patients throughout the morning and process them all in the afternoon, or collect in the afternoon and process at the end of the day.

Post-fixation: The amount of time once the sample has been fixed and frozen, to when the sample is actually run on the cytometer and data is produced. This can be on the order of months, or even years.

Drug developers care about this measure because it can tell them how long the sample is stable for. For trials that run for 24 months, drug developers want to know that they can get the same quality of data from the 24 month-old samples from their first patient as their most recent patient.