We have had a few patients that the doctor alerted us to that had a higher normal range platelet count on our LH500 that had also been tested at other labs and their results were lower, normal range.  We did a study comparing our results to our main hospital lab's (we are a Cancer Center clinic) results to ours and their is a definite positive bias.  Is anyone else seeing this?  We also looked into the fact that we run our CBC's almost immediately after being drawn and the data comparing immediate results to 2hour post draw results didn't really confirm anything.    

It may have something to do with the EDTA equilibriating with the specimen.  We will get false high Baso counts when a specimen is run about 10-20 minutes after it is drawn.  Do your PLT histograms look normal when this happens with the platelets?  Could also be a background issue.

Anyway, suggest you call Coulter and ask for advice.

Scott