I have been a Med Tech for many years (disabled now). The high anion gap can be caused by so many things. I remember metabolic acidosis, dehydration, Diabetic ketoacidosis, Lactic acidosis, starvation, alkalosis, hypokalemia, and hypomagnesemia. If you are taking a diuretic this COULD be the explanation. I had trouble with my lab work when I was taking lasix all the time. Now I take it only when I am feeling puffy. I hope this is nothing bad but I would bring it up with the doctor.