My hb1ac is 4.3, is it good or bad?

Perfect!: Hb1ac has an upper limit of normal of 5.5 this test does not change quickly; only if your diet, exercise, and/or weight have changed a lot will it change. Diabetes mellitus is diagnosed by this test at 6.0. So if you are healthy, your result should put you at ease. If, however, you rdoctor suspected diabetes, then the lab test may have been in error and needs repeating.