This really depends on the biology of the sample, on the cell types of interest, and on the specific analytes that will be measured. There are a number of investigations dating back to the 1990s looking at how long blood samples could sit, and at what temperature, before phenotype analysis by flow cytometry. Smart Tube reagent systems will preserve the phenotype as it is when the reagent system is used to stabilize the blood sample --- but it is biology of the sample that determines whether phenotypes change while the sample is still live and sitting in the blood collection tube.
Of course if you wait too long and there is significant hemolysis, coagulation, cell death, or granulocyte degranulation, then the sample cannot be banked with Smart Tube reagent systems. This is not typically a problem for most blood samples within 12 to 18 hours of collection, especially if the blood sample is cooled to ~10 degrees Celsius (ie. cool, but not cold enough to induce cold-activation).
If working with blood from a healthy, normal donor, kept at room temperature (~10 degrees Celsius is even better) then most markers will tend to show very little change over the course of 12 hours or even 18 hours or more. However, if you are dealing with blood from a donor with certain types of conditions such as high levels of inflammatory cytokines (ie. viral infection), sepsis or a lupus patient experiencing a significant flare, some markers may change significantly over 12 hours and you may even see non-trivial apoptosis in some cell subsets. Likewise, if investigating cell cycle in specific populations of cells present in human bone marrow, it may be necessary to work quickly and employ specific techniques to best capture the cell cycle state at it existed in vivo (see publications by Behbehani et al, 2012, 2015 and 2018).
The Publications Page of our website has a number of studies that used Smart Tube products to bank samples from both normal donors as patients with a wide range of conditions. Some of these publications discussed the unique challenges of collecting samples for their specific investigation.
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