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Dr. Bill's Commentaries

Three Hundred and Seventy Three   (December 31, 2010)

The other day (or more correctly, the other night), I checked my blood glucose level at 2:31AM. I had awakened, and as usual, checked my CGM monitor to see whether things were okay. The CGM glucose value was a bit "off" from perfection (in the low 120's, as I recall), so out of curiosity, I got out my BG meter to see what the number really was.


No way, Jose! I don't think I've ever had a value that high. First things first: I checked to see if my insulin pump's catheter was still stuck into me. Yes, it was. Next, recheck my BG, from another fingerstick in another finger.

Repeat 135.

Much more like it. But I still had the problem: why did the first value only a minute earlier register so high? I have no idea. One possibility might be recent intake of lots of carb, or maybe stray glucose on the skin of my finger (or so I've heard), but I hadn't eaten since supper many hours earlier, and can't think of any reason my skin would be so much sweeter on one fingertip than on another. Maybe someday I should saturate a fingertip in glucose and see what the value on my BG meter would be, but I haven't had the curiosity to do so (yet).

And if my BG were truly 373, it might have been an early indicator of impending viral or other infectious illness: the stress of such illness can cause severe hyperglycemia before more traditional symptoms such as fever or chills or cough or what-have-you. But the second value pretty well eliminates the possibility that the high value was from an impending illness.

"Lab error" is a more likely explanation. Sometimes, for reasons that can't be defined rationally, any testing procedure can have an unexplained glitch, and the numerical result will be way off from what it should be. And no one can figure out why. As long as it happens extremely rarely, or as long as the difference between "true" and reported values are fairly close, it's no big deal.

If the lab error had been the first warning of an impending flaw in the BG meter or the BG strips, then one might imagine that more weird results would occur over the next few days -- but so far, knock on wood, no more bizarre high BG levels while using the same meter and the same batch of strips.

Scary: if I had only done one BG test, and it had been 373, and I had reacted to it by giving extra insulin, surely I would have had a nasty hypoglycemic episode soon after (assuming the "true" value was about 135).

But the 373 vs 135 comparison opens up another, more philosophical issue: why was I so willing to accept the second value than the first? I've been mulling that one over for the past few days, and come to the conclusion that the report of 135 was (a) more consistent with my usual values and (b) was reasonably consistent with the CGM glucose value. Further, I didn't feel "sick." Had the value been truly 373 rather than 135, then I might  have had some symptoms of the high sugar, such as blurry vision or dry mouth.

But it is interesting: if a number is more-or-less what you had anticipated, you accept it without complaint. But if it's hugely different from your preconceived idea of what to expect, you simply don't believe it, and repeating the test is the logical next step. And if the second result is in line with expectations, ignore the first result.

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Dr. Bill Quick began writing at HealthCentral's diabetes website in November, 2006. These essays are reproduced at D-is-for-Diabetes with the permission of HealthCentral.

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