Sunday, November 27, 2011

Adjusting the Carb Ratio

Looking at Karl's blood-glucose logs yesterday, we discovered that Karl hadn't had low blood sugar once in two weeks, but he'd had high blood-sugar many times. Since insulin is what brings his blood sugar down to normal, being never low but often high means, "too little insulin."

We use what's called "advanced carb counting," meaning that we figure out the grams of carbohydrates in every meal and divide this number by the "carb ratio" to get the number of units of insulin. 

I'm told that Type 1 diabetics whose bodies no longer produce any insulin have a carb ratio of around 8, meaning they get one unit of insulin for every 8 grams of carbohydrate. For Karl, we've been using a carb ratio of 16, meaning that he gets only half a much insulin as the diabetic with no insulin production of his own. This implies that Karl's pancreas is working at half efficiency.

Frequent high readings means that 16 is the wrong number, so we started using 15. The two numbers don't sound very different, but on a typical meal this happens to give Karl an extra half-unit of insulin. We've only been doing this for 24 hours, so the results aren't definitive, but it did exactly what we wanted: his post-meal ("post-prandial") blood sugar was in the 120 range, and his pre-mail blood sugar was in the 80-100 range -- both very good numbers!

It may also turn out that Karl's poor blood-sugar control with higher-carb meals was a simple "not enough insulin" problem.

One thing I've found frustrating in the literature is the weak, hand-waving descriptions of how to adjust insulin dosage. Come on, guys, this is the Age of Science! Is it possible that the problem is that, if you're clear, you might be sued, but if you're incoherent, you'll be left alone? Because basic information is so often mumbled when it needs to be shouted from the rooftops, and this means I haven't found any good "How to adjust your insulin dose" links for this post.

What we do is look at the trends for the last two weeks or more, especially comparing the frequency of lows compared to highs. Lows are scarier than highs, which is reflected in the normal guidelines, where it's considered okay to have several times more highs than lows. If that's not what we're seeing, then our dosage or our technique are not right. 

If your glucose meter comes with adequate software, as the Bayer Contour USB meter does, then you want the averages to be where they should be, the standard deviations to be as small as possible, and the highs and lows to be under control, biased towards modest highs rather than modest lows.

The standard deviation tells you how tight your control is but not whether it's centered around the right value. Getting tighter control, for us, happens when we:
  • Reduce the number of carbs eaten
  • Calculate the carbohydrates in each meal accurately
  • Use the Novopen Junior for its half-unit dosing (insulin pens that only give insulin in one-unit increments are too imprecise)
  • Don't cheat in any way.
Having mealtimes at the same time every day doesn't seem to matter for Karl, and if the portion sizes vary, this doesn't matter either if we've figured out the right carb ratio, so long as he doesn't go crazy on the carbs.

Random diabetes tip: The Swiss Miss sugar-free cocoa is sorta thin and unsatisfying, but adding a tablespoon or two of cream into the mix straightens that right up with only 1-2 grams of added carbs. (Avoid their "No Sugar Added" cocoa, since it's full of sugar.)

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