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Comment by adevine | Hacker News Reader

Getting 6-9 drops of blood from a finger tip is not easy - you have to ask "Is it really a benefit over a venous draw if it's much more difficult?" At some point I think it makes it easier to instead just focus on super-fine needles, and the need to draw less blood, from venous draws.

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"Super-fine" cause mechanical haemolysis and will give inaccurate results for many routine blood tests

For anyone who isn’t a doctor / biologist: “Mechanical hemolysis” means the needle is bursting red blood cells, leaking their cytoplasm into the blood plasma.

Yes, that's true. I had thought about simply squeezing the finger to get some more but that appears to be a problem for the results too:

> Morris et al7 believe the higher variability of capillary blood compared with venous blood is due to the presence of extracellular fluid in capillary samples. In clinical practice, milking of the finger by insufficiently trained health care workers may result in even greater drop-to-drop variability than shown here.

http://ajcp.oxfordjournals.org/content/144/6/885.full

It's a very interesting problem. They didn't even see all the donors end up with the same average from drops as from a venous draw.

I seriously don't feel any pain 50% of the time I give blood and when I do it is a very mild prick. Usually its just the rubbing alcohol didn't all evaporate.

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