It is even worth as the platelet does not alter the scatter profile of the cell but might make the event positive to the platelet specific CD marker. This is why when monitoring monocyte-platelet aggregates you also have to consider platelet -monocyte coincidence which you can normally also observe on the neutrophils. Now obviously a lot of people just say flow rate but do not explain what they mean. Coincidence rates depend on particle concentration and the sample volume flow, beam geometry, flow channel geometry, sheath flow and worst of all statistics. It can also lead to interesting data distributions (clusters, histograms ...) depending on the way signal processing is performed and has serious implications on cell sorting. If you realised the problem try to publish with "air" By the way what is the probability of coincident birthdays in a small crowd of 23 people? Enjoy the puzzle Gerhard I always wanted to add one of these statements below The generation of random numbers is too important to be left to chance - I use science -----Original Message----- From: Kenneth Ault [SMTP:AULTK@mmc.org] Sent: Wednesday, May 29, 2002 8:48 PM To: Cytometry Mailing List Subject: Re: Flow rate question This brings up a very important issue that we platelet types have struggled with frequently. The important flow rate is the total particle flow rate, not the rate of particles "seen" by the machine. Thus the rate that you need to be concerned with is the rate with no thresholding or live gating. Coincidence events often occur between "seen" particles (those above the threshold) and the potential myriad of particles that are not seen, but are still there in the observation volume at the same time that a "seen" particle is present. I don't believe that there is any absolute flow rate that you can use as a guide - you simply have to show that the frequency of the events of interest, or the properties of those events, is independent of particle flow rate - if it is not, then you may be dealing with coincidence. Ken Ault
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