CBC Collection Method Question - Effect on Results?

So, in really "debugging" and thinking about my recent inconsistencies in platelet counts, I have started to think about the effects of the method of collection. My previous hematologist's office always used venous collection for my CBCs. In my first visit to the new doctor, the machine in the office was broken, so they did a venous collection and I got a count of about 60. The next two weeks, the machine was working again and my CBC was done using a fingerstick (and I ended up with counts of 21 and 23). I hadn't had a fingerstick since I was a kid managing my ITP. I didn't really think much of it at the time, but now I'm really wondering. I stumbled across the following article:
www.ncbi.nlm.nih.gov/pubmed/9365861
which talks about fingerstick platelet values being 20% lower (and poorly correlated r2 = 0.43) than venous samples. REALLY???!!! This might explain how I am so completely asymptomatic at such "low" numbers for me. I also wonder about my platelet size because of the promacta and potential error introduced because of my different platelet morphology. I also found another article that talked about the coefficient of variation (CV) for fingerprick blood being higher by 4 times for platelets. I don't speak statistics, but this all sounds quite fishy and I want to demand venous collection to compare with these fingerprick numbers that I now don't quite believe.

The plot is thickening. I am going to investigate things from this angle. I don't want to make treatment decisions based on bad data!

How do you all get your blood work done? All my other hemos from my adult years have used venous collection, but that is naturally a small sample. Anyone know anything about this topic? Thanks for helping me as I continue to "debug" my condition. Once a computer scientist, always a computer scientist

This subject came up years ago. At the time, we couldn't find much info on it but with the little we did find, we all agreed that finger sticks were not accurate. That probably doesn't help much, but it's what I got!

P.S. It was mostly the kids who got the finger sticks. Adults, not so much. There used to be a lot more active parents on here.

Thanks for the speedy reply Sandi. You are like the awesome archives of so many years of questions all rolled into one!!

It sounds like exactly what I'm guessing regarding fingersticks and their accuracy. I'm going to try to see if we can either do both for the next two lab appointments to compare, or, barring that, request venous collection and see if that will fly. Luckily the new office has a convenient method to send online messages to doctors, so I typed up a nice summary of my concerns and sent it to the new hemo. It really helps that the machine was broken that first week I went, and I ended up with a count of 60 via venous collection. My little wheels started turning, though of course counts do wacky things as we all know :lol:

Thanks again for your response!

Haha archives! I guess I am the archives.
It would be interesting to see the comparison if you can pull it off!

Good catch Mom. Impressive.

Once upon a time I was researching getting my own hemocytometer and related equipment to do finger stick count tests at home. What I recall is that the greatest error factor is the actual finger stick itself. As I recall clumping (and clotting?) is a huge problem. Once you stick the finger the bodies chemical reactions immediately go into action for the platelets to hook together and stop the bleeding - at the site of injury. So it becomes imperative with finger stick to get the blood really flowing, without restriction, with the stick and to collect it without any delay.

With a long needle the problem is vastly less. The blood is collected before it gets to the site of the injury and there is little delay time between the stick and the collection.

Is this where the 20% comes from? I dunno...