I'm not sure if its ever been quantified anywhere. One way to sample it I guess is to aspirate all the time and see if any blood gets drawn up and start to aggr

I'm not sure if its ever been quantified anywhere. One way to sample it I guess is to aspirate all the time and see if any blood gets drawn up and start to aggregate some simple incidence rate on the number of occurrences one experiences over time and the total number of injections given. From what I heard that whole process fell out of favor to optimize for comfort and rapidity over the possible futzing with a syringe still embedded in the body.