Why do type 1 diabetic patients have to increase their hemoglobin a1c?

A1c a control marker. A1c is a long term marker for glucose levels in the body. It will go up to higher levels when the blood sugar levels are above recomended levels and declines when you keep your sugars in a healthy range. Since the sugar level can go up or down dramaticly over less than hour, A1c is a better overall gage of long term control than your test diary (& you can't fudge the value).

Related Questions

Could eating more carbohydrates increase a hemoglobin A1c test in a non-diabetic?

Probably not... Your body has an incredible ability to regulate blood sugar levels and when this ability is intact, excess carbs will be converted and stored as fat, thus should not raise your a1c. Once the ability is diseased, the excess carbs/sugar stay as sugar, thus higher blood sugar in diabetic, and will raise your a1c over time. Moderation is key. Live a well-balance life. Live long. Consult doc. Good luck.
No. Inappropriate glucose metabolism and Insulin deficiency or resistance will increase the intracellular red blood cell glucose concentration.

If my hemoglobin A1c = 5.7%, am I diabetic?

Probably not. This is below the threshold of diabetes, but it is only one test for diagnosis.