Which Finger-stick Reading to Trust?

Diabetes Technology Glucose Monitoring
1

I understand there is some variability between the reading from different fingers, but anyone have results like I got a little while ago?

11:40 83 Right Index Finger
12:11 144 Right Ring Finger
12:12 88 Left Ring Finger
12:13 101 Left Thumb
12:14 94 Right Thumb

I was getting ready to have lunch at 11:40, but the UPS driver arrived with some stuff I ordered, so I did not eat or Bolus at that time.

I checked again right before actually eating.

I had been running a touch lower than normal since late last night. Values in the 80-90 range. So when I got the 144 I checked again...glad I did! If I would have accepted and bolused for the 144, I would have been in trouble!

Same procedure for each finger, new lancet for each, hands washed before the 11:40 and again before the others, etc.

Meter (Bayer Contour Next Link) tested with control solution was within range.

Anyone else run into such a huge variability between fingers?

I don't use the CGM for treatment decisions, but it's nice to look at trends, but sometime it just adds more questions:
11:38 130
11:43 122
11:48 116
11:53 93
11:58 97
12:03 96
12:08 94
12:13 93
12:18 91

So was the 83 @ 11:40 skewed or was it the 144 @ 12:11?

If the meters are only accurate within 15%, and the CGM is only 15% too, and my finger-sticks are as much as 60% difference, then having to account for the time lags...it's no wonder Diabetes is such a challenge to manage.

Rhetorical question: Do we need to make extra confirmation finger-sticks before making a treatment decision?

Maybe I'll do that for a little while and track fingers...heck, might just track each individual stick location too. Which means I need to draw up a finger tip map.

2

CGM is advertised as having a 20 minute time lag. So the 11:58 result of 97 would be the number to compare to the finger stick 83. Maybe a little low, but very similar really (within 15%).

Your average finger stick BG from 12:11 to 12:14 was 107. These four results are all within about 15% of the average value, except for the 144 which is 35% off. Its possible the meter was off for this test, but also possible the test was invalid (not quite enough blood, finger not quite dry, etc.). Not enough data to know for sure.

I once tested my BG response to different sugars (banana vs. glucose) so I could graph it, and found a single outlier that didn't follow the otherwise smooth graphs I made. So yes, I've seen the same thing as you; but also like you, I couldn't be sure whether that was a single bad meter result or bad testing methodology on my part. I don't re-test unless I think I've screwed up; the results are close enough almost all the time that it seems really unnecessary.
3

That's my usual routine as well: If something does not look right, test again.

If I had not done so this time (and not been aware of what my BG 'should' have been) I would have bolused for 144 instead of 100ish and ended up having a very bad afternoon!

I probably would have ended up in the 20's instead of 69/64 like I am now!
Perhaps my reliance on the 94 was a bit optimistic as well.

The good news in all of this? I get to have a snack now.... :-)

ETA: Used up three days worth of test strips just for lunch today!

4

Do you use control solution?

I am still very new at this, but I now check each new vial of test strips with control solution at least twice before I test with it (OneTouch Ultra2). Although the vial gives a large range for spec, the actual behavior looks like the control solution is 120 mg/dl. The only vial I've discarded gave very variable readings similar to what you report: 85,118,126,124,112 (I kept testing 'cause the 85 was so strange). The one after that was 122,123,124 (I was paranoid, 3 control tests) and the next 117,118 (I now always do the control twice). Bad test strips seem more likely to me than finger-to-finger variation.

ZZ

5

There are so many variables that can influence a BG reading, so don't ever let one odd reading throw you off.

First, when you get a weird one, like that 144, toss it and take 2 more under very carefully controlled circumstances. My protocol when I have to do this is as follows:

  • Thoroughly wash hands with soap and water, make sure well rinsed off and dry (again, if already washed them)
  • prick finger, squeeze out about 4x as much blood as I actually need for 2 tests.
  • Drown the little receptor tab on the Freestyle strip (there are two of those tabs) in the blood drop until the tester beeps, then remove the strip carefully, preserving the blood on the finger for the second test.
  • Get first result, repeat with same blood draw on same finger.
This always works for me. The two tests always come out within 5-10 mg/dl of each other (actually the +/- 2-3 most of the time); almost always quite different than the bizarre reading I got, and always much more "sensical" as to how I feel, how much IOB I have, how long it's been since I ate, etc. etc. etc. -- i.e., in line with what my diatuition (I just made that word up!) tells me it should be.

After having this happen a few times, I used up about 10 strips seeing if I could cause some weird readings even though the meter beeps, presumably indicating a good sample.

I found that, with the Freestyle strips at least, it's real easy to get an insufficient sample even though the system says it got enough, and wind up with a bogus high reading.

Hence my "drown the strip in blood" step above... :-)

6

Those are all actually reasonably close except for the 144 which could have been an error or from food residue on that finger. If I get a reading that doesn’t make sense to me I just wash my hands and do it again and the first reading is either proven wrong if its way off or reaffirmed if its close. You’ll lose your mind trying to be a whole lot more exact than that, it’s just not an exact science-- that was really tough for me to accept but now that I did it works out better

7

Yes, I tested with Control Solution. Level 2 (presumably manufactured to be 130 mg/dL )should result in a reading between 115-144 according to the vial
I got 136 & 128.

8
diatuition

I suppose this is a good take-away from this discussion. Especially for the newly diagnosed.
It is critical to get to know how your body responds individually to the disease, food, exercise, stress, medications, etc.
And as a reminder to not blindly trust any one specific test or citation in the medical literature, or even advise.

Everyone is different. Learn how your body reacts. Develop your own "diatuition".

9

My opinion: Control solution is a complete waste of time. The passing range is so huge it doesn't really tell you anything other than "your meter, or test strips, are completely botched".

The best "control solution" in my experience is my own blood. When I get an odd reading, I take a few more, more carefully, and compare them to my inner diatuition about whether or not the readings seem right.

10

If I think a reading is wrong I retest on the same finger sometimes and if it's close I assume it is right. I have had some crazy readings though from 400 to 43 which were totally wrong. I'm not sure what caused the 43, but the 400 was definitely something sugary on my fingers. It seems like the 144 was an error here .

11

The Medtronic cgm says 130 down to 90. The blood test says 83 up to 105 (average of 4 tests). The one that’s way off is the cgm. I found that cgm to add to confusion too. I switched to DexCom and it is accurate enough to not be confusing.

12

Dave,

I completely concede your point on the ridiculous 'spec ranges' on the vial. It is some kind of legalistic weasel-wording. I simply reason that control solution is made at some standard concentration that they don't tell us so that they can say that a basically bad batch of strips is still 'within spec'. I DO NOT know that it's 120 mg/dl; that's just a round number.

Also, it seems reasonable to think the control soln concentration, whatever it is, doesn't vary between tests, so wildly varying readings point to bad strips.

13

I agree with Dave. Strips are a buck each and the information you get from using control solution just doesn't seem worth a buck. I don't think I've used control solution is five or six years.

Even with control solution nicely shaken up so that the glucose is evenly distributed you can still get a reading of + or - 20%. You get two readings of 80 and 120 and what have you learned?

14

That is most interesting! I usually use my thumbs due to the good blood supply.