I've had low serum creatinine for the last two years, as low as half the bottom of the normal range, and my endo says that this is called hyperfiltration and sometimes happens to type 1 diabetics as a kind of kidney disease, when the kidneys are overactive.
If you do have this, do you get stomach aches from drinking water?
And if you used to have this, can you say how long you had it and what happened with your kidneys afterwards?