If it's a clear insulin, make sure it hasn't become cloudy. In both clear and cloudy insulins, make sure you don't see any crystal formations. Then, the way to tell if it's still good is to use it...if your blood sugars act as expected, then it's okay. If not...throw it out.
I've used insulin past the expiration date, but usually I make sure my pharmacy gives me insulin with a date far enough in the future that I'll use it before it expires.
Yes, I agree you've got to be careful, and test, test, test. But I once had a mix-up with my mail-order pharmacy, and ended up with no extra insulin for several weeks. I used the expired insulin with no problems (it had been kept refrigerated, and while I don't usually keep an opened bottle in the fridge, I did with this one since it was past expiration date.) My blood sugars were fine, so apparently the insulin was still fine, too.
I no longer order my insulin through the mail, but get it at the local pharmacy. It's just too darned scary to have that happen.
im using the novolog flexpen and my readings are really strange, it looks clear and nothings floating in it so i think its fine. but how would i really know???
i have been raising my insulin units up and it seems the more i raise it the more insulin i need.
i wat taking 4-6 units last week before meals, now this week im at 13 units before meals.
We've had problems like that too. My daughter's numbers were going way up and it seemed no amount of insulin would cover it. We didn't see a problem with the insulin but we opened a new bottle anyway. Her numbers still were very high even after that and it was several weeks before we got them back in control. We still really don't know what the cause was.
I guess my point in all this is that yeah, sometimes that happens for seemingly no reason and it may be worth it to get new insulin just to rule that out.