1. fluctuation of sugar can be due to the fact that he might not Eat during the night, i.e. missing or delaying a meal [fear of high blood sugar level], and taking his anti diabetic drugs/insulin as usual causing decreased blood sugar level in morning.
2. Also in kidney disease, there is reduced excretion of insulin, resulting in hyperinsulinemia
and probable low blood glucose [adjust the dosage, if seem necessary by your Doctor]
3. if serum creatinine
is raised, avoid protein rich diet, but biological protein (essential amino acids) can be given, also check with potassium levels [avoid tomato,papaya,banana,cheese,coconut water,fruit juice, leafy vegetables, if it is raised]
4. as he has diabetes with kidney disease, possibly has developed diabetic nephropathy
, and following renal involvement hypertension
follows which can be dangerous because of existing heart [by pass] disease.
PS: give attention to retinopathy
, nephropathy, neuropathy.