The journal Diabetes Care this month has a fascinating study about basal-bolus insulin therapy for T2DM, titled Adjust to Target in Type 2 Diabetes: Comparison of a simple algorithm with carbohydrate counting for adjustment of mealtime insulin glulisine. The authors compared two algorithms for adjusting mealtime rapid-acting (bolus) insulin and background (basal) insulin in 273 patients with type 2 diabetes over a period of 24 weeks. The simple algorithm group was provided set doses of bolus insulin to take before each meal. The other group was provided an insulin-to-carbohydrate ratio to use for each meal and adjusted their bolus dose based on the amount of carbohydrate consumed ("carb counting").

Before you say "Huh?", let me do some explaining about basal-bolus insulin therapy.

Most people are aware that a single shot of a single type of insulin given once daily isn't enough to accurately mimic the pancreas' output of insulin. So programs of insulin administration for the past thirty years or more have emphasized the need for multiple daily injections of different types of insulin. Most of these programs are set in concrete, with little variability in doses possible from one day to the next. Sometimes two shots a day are given, mixing two types of insulin into each shot. Sometimes three shots a day, with a mixture in the morning, a supper dose of rapid-acting insulin, and a bedtime dose of long-acting insulin. Usually, doses are adjusted every few weeks or months, based on overall trends of blood glucose and A1C. These programs, and many other variations, are still widely used for type 2 diabetes, where it's assumed there's still some residual pancreatic production of insulin that can help maintain the blood glucose levels.

But in type 1 diabetes, where the pancreatic beta cells have failed almost completely, and can't make and release any worthwhile amount of insulin, it's become standard therapy to use what's called "basal-bolus" insulin therapy. Basal-bolus insulin can be given by using rapid-acting insulin in an insulin pump, or by using injections of rapid-acting insulin (Humalog, Novolog, or Apidra) at every meal, together with long-acting insulin (Lantus, Levemir, or sometimes NPH  or Ultralente) injected once or twice daily.

The basal dose is designed to mimic the background, minute-by-minute release of insulin by a normal pancreas. The basal dose is usually kept stable from day-to-day, and adjusted periodically based upon general trends and specific markers, such as middle-of-the-night and/or dawn blood glucose levels.

The bolus dose is designed to mimic the release of insulin in response to meals by a normal pancreas.

In basal-bolus therapy, the bolus dose that is given may vary from meal to meal, based on numerous factors, mainly the amount of carbohydrate in that meal, but also the blood glucose level at that moment. Sophisticated dose adjustments might also take into account more factors, such as how much insulin is on board from a previous meal, any planned upcoming exercise, stress levels, and even time of day. Sounds pretty complex, and indeed it is.