Most flow cytometry samples are processed, stained and then run on a flow cytometer, and these protocols may take a few hours but can also span the greater part of a day. Protocols take even longer when many samples needed to be handled, which is often the case with clinical samples. How do you handle staining and running large numbers of clinical samples while also trying to pull an all-nighter? In some cases, a fixative can be added to stained cells so they can be preserved in their stained state, refrigerated, and run on a flow cytometer at a later time. Consider these factors to help you determine if cell fixation is a good option.

1. Sometimes only fresh cells will do. Certain cell types and staining protocols can tolerate fixation, such as the case for surface staining of T cells. Other cells are sensitive to fixation and cold storage and can only be processed and run as fresh samples. Be sure to run a pilot experiment that includes fixed and fresh cells processed and stained under the same conditions to determine how fixation and storage alters your flow cytometry read out.
   
   
2. Consider your staining timeline. If you have a staining protocol with numerous staining and washing steps and lengthy incubation periods, you may have to consider starting the process early in the day if you want to run your samples before midnight. Fixation may be another option to buy you some sleep before running your samples on a cytometer.
   
   
3. Hardware constraints. Flow cytometers are typically shared instruments or owned by a CRO and may not even be located in the same building as your lab. Consider how running fresh or fixed samples may influence your access to an available flow cytometer. Cell fixation can you give a wider time window during which you can run your samples.
   
   
4. Large numbers of clinical specimens. Clinical trials with several hundred participants may result in thousands of cell specimens to process, stain and run on a flow cytometer. Ideally, a validated flow cytometry assay is used to evaluate these samples, as this assures your assay works consistently between users and at different times. You may still have several hundred samples in a single run, and cell fixation may be a good option to make the size of your flow cytometry runs more manageable.

Fixation may be a time-saver or it could destroy your cells. Be sure to figure out if fixation works for you.