I’ve measured my fasting blood sugar (= blood sugar before breakfast) for about four years. I began out of curiosity but became alarmed when the values approached “pre-diabetic” (> 100 mg/dl, diabetic is 126 mg/dl or so). Eventually I learned that walking an hour/day put them in the 80’s consistently. Perhaps 84 is optimal, who knows.
I have used Abbott test meters and strips. They need so little blood that testing is painless. Recently (January 2012?) Abbott introduced new “butterfly” test strips that “wick” the blood. The meters stayed exactly the same. The new test strips are certainly better. I started to use them. I started using them after a gap (a month?). All of a sudden my scores were about 5 mg/dl better — for example, 84 instead of 89. I assumed this was due to lifestyle changes on my part. I was walking more, I was more muscular, whatever. These were plausible explanations. Surely Abbott had not corrected a huge mistake (given the size of the business, the importance of diabetes, and the need for accurate test strips, to be consistently off by 5 mg/dl would be a huge mistake).
Now I wonder. I recently found some old-style test strips, barely expired (2012/04). I have compared them to the new-style strips (expiration 2013/06). Here are my results:
Morning 1. New: 81, 84. Old: 99, 91, 100.
Morning 2. New: 80. Old: 96, 94, 95.
Morning 3. New: 84. Old: 104, 97, 105.
Morning 4. New: 86. Old: 101, 100, 100.
These results involve three different meters. The old strips come from three separate vials. It is clear that the old strips produce readings much higher (about 15 mg/dl higher) than the new strips.
The old strips are expired but I doubt they got 15 mg/dl worse in 1-2 months. I expect they are accurate when they leave the factory and slowly get worse. Now I have some idea of how much worse (and in what direction). Apparently there is a big increase in bias with little increase in variability. I’ve gone from batch to batch before and never noticed a difference. Only when comparing the new strips with the old has a difference been clear. The earlier comparison, with a 5 mg/dl difference, compared unexpired old strips with the new strips.
I conclude that with the old strips, deterioration with age is worse than I expected and I should pay more attention to test strip age.