First BG reading may not be accurate



After getting a BG reading of 58, I did a little searching on here to see if I should be concerned. Another poster (I didn’t bookmark it and I couldn’t find it when I searched again, so I hope he will chime in here) said that he always tested twice because he has Reynaud’s and thought that might affect his first reading, i.e., that the blood closer to the surface of his extremities might register lower BG.

While I don’t have Reynaud’s, my fingers do get very cold during my daily fasting window, so I thought I would conduct a mini-experiment to see if I had the same results. I waited an hour, and then re-took my BG. It was down to 56. I immediately took it again - 64. Again - 67. Again - 69. Again - 70. Again - 69. I did not get a consistent reading until the fourth try, and they were each taken within seconds of each other.

My VERY unscientific conclusion is that there could be a correlation between “first blood” taken from the extremities and lower BG readings, and that if you take blood that has been circulating, the reading may be higher.

Anyone else have this experience?

(bulkbiker) #2

More likely to be the inaccuracy of home blood glucose monitors…
Here in the UK they are allowed to have a 15% variance simply due to the way they work means they aren’t especially accurate.I’m guessing it will be similar where you are so 58 -70 could be a reading of 65 but variations in the strips could lead to the confusion.

(Bruce Burkhalter) #3

Over the years I’ve collected a veritable fleet of blood glucose meters and been frustrated by their general inaccuracy. I’ve actually drawn finger tip blood and tested several meters from the same drop. I’ve actually had a 70 point (U.S.) difference between meters. Even meters of the same type using the same strips. Accuracy seems to also vary with the batch of strips. That said, I’ve learned I must use judgement and Dr. Bernstein’s law of small numbers reduces the consequence of mistakes. My ultimate test of a meter is when I feel the threshold of a low I know I’m below 60 (U.S.) and a meter agrees or not.

(Bunny) #4


Thank you all for the thoughtful responses. Makes so much sense!

An interesting postscript: I repeated the experiment yesterday during my fast, and once again, the readings were higher, and finally stable, only after the fourth (BG reading stabilized at 72, 72, 71, 72 at 4th, 5th, 6th, and 7th reading, respectively). I will keep experimenting while fasting just for fun :blush:.

(Bacon enough and time) #6

As long as you feel all right, you don’t need to worry about a low glucose level. The “normal” range was determined by studying a population that is mostly eating a high-carbohydrate diet, so I would guess that it is actually quited skewed.

Dr. Stephen Phinney sometimes talks about an experiment done quite some time ago now, in which fat-adapted athletes were treated with insulin to drive down their blood glucose to extraoridnarily low levels. At levels that in non-fat-adapted people would have caused coma or death, these fat-adapted subjects were perfectly fine. This suggests that the brain is quite capable of thriving on β-hydroxybutyrate and may not even need glucose at all. (Our red blood cells definitely need glucose, however, which is why the liver produces a certain amount of glucose when we drop our carb intake.)

Peter, the author of the Hyperlipid blog, makes the point that once we become fat-adapted, people’s serum glucose tends to rise, even though their HbA1C level remains low. The explanation for this is that the muscles, having adapted to metabolizing fatty acids in place of glucose, are refusiing to take glucose in, so as to spare it for the cells that cannot do without it. (This is called “physiological insulin restance” or “adaptative glucose-sparing.”)