Q: When I was first taught how to use NPH insulin, I was told to roll the vial between my hands ten times before drawing the insulin. Why?
A: Certain types of insulin: NPH, Lente, and Ultralente insulin, look cloudy in the vial. They look cloudy because particles of insulin are not fully dissolved. When the insulin bottle or pen sits still for a few minutes, the particles of insulin settle out, and fall to the bottom of the container. Before you draw the insulin, you need to gently mix it up so the whole bottle has the same concentration of insulin all the way through. If you carry prefilled syringes, and they have any of the above "suspension" insulins in them, you'll need to gently agitate them, too, for the same reason. Otherwise, you would get different concentrations of insulin when you draw the clear part than when you draw the part that contains the settled particles.
Rolling the insulin between your hands is a good way to mix insulin in a vial without making a lot of little bubbles in the insulin itself. If you shake the insulin and mix in a lot of bubbles, they will not hurt you. But you might end up with little bubbles of air in your syringe, and that would mean you would not get your full dose of insulin.
Q: When I started using an insulin pen with an NPH mixture, I was taught to mix the insulin by rolling the pen ten times, and then pointing the pen up and down ten times. Is this really necessary? Why?
A: Research has shown that insulin in pens is a little harder to mix than insulin in vials. There are no air pockets to help the mixing process. When people roll the pens in their hands, the insulin can still have layers that are not completely mixed. But there is a tiny glass ball that rolls back and forth when the pen is pointed up and down. By doing this ten times, you may be sure all the layers of insulin are thoroughly mixed.