Moving Targets: Adapting to Meter Inaccuracy


So this was weird:

I wake up from a dream at about 12:30 AM. My continuous glucose monitor (CGM), which I had inserted and calibrated once before going to bed, showed a blood sugar measurement of 99 mg/dL. Perfect, I think to myself as I stumble out of bed toward the bathroom. I measure my blood sugar on the OneTouch UltraLink I keep on the bathroom counter so that I can enter the second calibration point into the CGM and not have to wake up again later in the night.

56. Eh? I don’t feel 56. I would feel it if I were that low, right? I should feel it if I were that low, at least.

I measure again on the UltraLink, to double-check, knowing that glucose meters can be inaccurate and sometimes way off for whatever reason (Something on my hands? Temperature? Contaminated strip?). Again, 56. Exactly the same.

So, despite not feeling low, I eat eight grams of corrective carbohydrates. As I’m doing so, I have woken up enough to realize, wait, I really don’t feel low. I don’t even feel like I feel after I’m low and don’t really feel low. I just feel normal.

About two minutes after my original glucose meter check now, not even close to enough time for the corrective carbohydrates to have taken effect, I measure my blood sugar on my other meter, a OneTouch Mini I keep in my purse. 95 mg/dL.

Oh. Really? No, but, really? I try again on the Mini. 93. OK; that, plus the CGM, plus how I feel, indicates that the 56 was probably wrong.

But wrong twice? And wrong to exactly the same degree twice? I’ve seen one really far off measurement at a time, or two really far off measurements that were also very different from each other. But consistent inaccuracy? That’s new. And frustrating– I accept that the meter will be inaccurate sometimes, but I would prefer the inaccuracies to be obvious, or to at the very least not give me two misleading measurements in a row so as to imply a statistically significant likelihood that the measurements are indeed correct!

I measured myself again on the UltraLink just for good measure. 83 mg/dL.

So what were those two 56 data points? I don’t know. The meter’s fault? The strip’s? Mine? Random chance? Sadly, I don’t know.

Working in software, I find that sometimes a mysterious problem arises that, after much debugging, proves to not be a software issue, but a hardware one– the hard-drive is making clicking noises, and is failing; or the server’s random-number generator broke, and so there is insufficient randomness available for applications on the system. In those times, I often have a sense that, well, the theory and the application code was perfect; it’s reality that keeps getting in the way. Literal, physical, atoms-in-space-and-time reality!

As a diabetic, meter inaccuracy, insulin pump clogs, and CGM sensor failures give me a very similar sense– in theory, everything works in perfect concert. Reality, though, is much rougher around the edges, and it is at this interface between concept and reality that I can get frustrated and hurt if I don’t keep a firm hold on the fact that, yeah, it happens, and therefore it is in my best interest to keep vigilant, reasonable, and flexible as new data comes in.

Luckily, in this particular collision with reality, all I lost was about five minutes of sleep.

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