There is no problems with keeping insulin in a domestic fridge, even in the door which I have done for the past 21 years, and hubby has done for 30 years... verious fridges along the way..
It is also prefectly fine to keep the insulin out of the fridge as well, although it's recommended that you only do this for a month, so generally will be the cartridge that is fitted to the pens that are in use...
I keep my vial that it in use sat on top of the fridge so it's room tempreture when I fill up my insulin pump cartridge as it helps to prevent air bubbles...
Extreme low tempreture which is around freezing point and extreme high tempreture that we don't tend to get in this country can cause problems...
So keeping your insulin in the glovebox of your car isn't a good idea, or leaving the pen and/or insulin on the window sill facing the sun isn't either...
A indictor that something is amiss, if you see crystals in the insulin or it looks lumpy or off colour to its norm then don't use it.. If for some reasons it doesn't seem to be efficent controlling your Blood glucose as it normaly does, and there isn't another reasonable explination that all of a sudden your bg's have shot up.. Replace the cartridge with a new one..