I've had Type II for about 10 years, and went to a diabetic education class at a local senior center with a friend who was newly diagnosed; some of the reading literature given out in this class surprised me, most notely about insulin absorption. The literature, which lists no author, says:
"In the past patients were taught to rotate insulin injection sites because the insulin preparations contained impurities which caused local reactions in the skin. With the new insulin preparations, purity of the preparations is no longer a concern and rotation of injection sites is now a common cause of day-to-day variability in glucose control. Insulin is absorbed fastest from the abdominal wall, slowest from the leg and buttock, and at an intermediate rate from the arm; at any of these sites, insulin absorption varies inversely with subcutaneous fat thickness. These differences can be useful clinically. Premeal regular insulin should be rapidly absorbed, and injection into the abdominal wall may therefore be preferable. On the other hand, slower absorption from the leg or buttock may be desirable with the pre-evening meal dose of intermediate-acting insulin to ensure a duration of action that lasts through the night.
The degree of insulin absorption is also determined by the rate of subcutaneous blood flow. Thus, insulin absorption is reduced by smoking and enhanced by any modality which increases skin temperature, including exercise, saunas or hot baths, and local massage. These effects are more marked with regular insulin than with longer acting insulins.
Both the angle of needle entry and the depth of penetration affect the rate of insulin absorption. Very shallow insertion can cause a painful injection into the skin which is not well absorbed. In comparison, a perpendicular injection in a lean area may result in a injection into muscle with more rapid absorption.
The recommended technique is to use an area of the body in which about one inch of fat which can be pinched between two fingers. The syringe, with a 0.5 inch microfine (27G) needle, is inserted perpendicular to the pinched skin up to the hilt of the needle and the insulin is then injected. It is no longer recommended to pull back on the syringe before injection or to remove the needle if blood is obtained.
The common practice of cleaning the skin with an alcohol swab before injection may not be necessary. As an example, a study found that there was no difference when the usual injection technique was compared with injections through clothing. The only problem with the latter was a occasional blood stain on the clothing."