FDA says BG tests may be inaccurate in these cases

Did you guys see this link? The FDA says these can cause false highs and lows.

I thought it was odd that they said that “Squeezing fingertip too hard because blood is not flowing” could cause a false low. Does anyone know why?

If you squeeze the fingertip then the blood drop will consist mostly of interstitional / tissue fluid. This fluid is not representative for the blood glucose in your brain or main blood vessels. It is 15 minutes behind and the concentration does not match with the calibration of the stripe.

I am a little surprised that Anemia leads to false highs and Polycythemia leads to false lows. I expected it the other way around. Thanks for the link.

I think there is one point missing: the accuracy of the meter depends on its age. It seems benefitial to get a new device after 3 years. This may be related to corrosion / damage on the sensor contacts. Also the self calibration via optical sensors may be impacted by aging.

Saw it but its not really new news, Think Like a Pancreas had a warning about milking your finger to forcefully in it.

I’m actually surprised that anemia matters since I believe the meters work by measuring glucose. It could be that anemia thins the blood and polycythemia thickens the blood, the reaction is timed, and if the blood is thick or thin it could distort the rate of reaction.

I’m also surprised that they go into all this trouble explaining all the sources of operator error when meters are only good +/- 20%.

I need to milk finger or most of the time it will not be enough blood.

I have to milk my finger. I have been pricking them forever.

I don’t get many lows, so I think this is a little wacky…

I wanted to follow up on this discussion. I have been paying attention when I test my blood sugar and there is no way that I can poke my finger and just have a drop of blood appear! I have to squeeze it somewhere.

What I usually do is to squeeze it further from the poked site and avoid pushing hard near the site.

I tried increasing the depth on the lancet device – it became really painful, but still no drop of blood appears without some pressure. Is there something that I can do so that I would not need to push to get blood out?

Also, I wonder if blood pressure level influences this? Mine is quite low.

I always have to squeeze even if I wash my hands in hot water. I wipe off the first drop, which means pushing down for more.

Does anyone here freely drip?

I’m with bsc! Big deal if we squeeze when the meters are far from accurate.

So I’m not the only one! I also use the second drop :slight_smile:

I didn’t know about this until a nurse told me when she saw me testing. She said never use the first drop because it has tissue & fluid. Someone who actually knew about diabetes!

I have experiences many false lows when squeezing my fingers hard. I try not to stick again, so I squeeze and then wind up wasting a strip, becasue I know it is wrong…and the 2nd sample always comes out higher - much higher by like 20-30 pts for me.

As opposed to squeezing your finger, what I do is massage blood up into the finger. If you press against your finger at the base of the hand and press on either side, squeezing between your index finger and your thumb, and moving up just against the two joints next to your hand, you can force more blood into your finger tip without squeezing out interstitial fluid. This is different than squeezing your tip which can force interstitial fluids out.

And measuring the blood sugar in interstitial fluid is still accurate, it just is delayed as Holger notes. In fact, the CGMS systems measure the glucose in interstitial fluid, which is why they lag behind meter readings.

Thanks bsc! This helps!

I am running my own experiments. Whenever I calibrate my dex and the first BG reading is not within 5 points of the dex readout I use a second BG strip. These are my findings:

  1. Clean fingers are most important.
  2. There is no reason to prick another finger for the second sample.
  3. Whether the first BG strip reads higher or lower seems to be random. No need to skip the first drop.
  4. A small blood sample or one that was helped by a squeeze tends to read lower. When the first drop is not big enough without squeezing I don’t waste a strip and just prick another finger.