Renal function test results are bad.

My grandfather aged 80 ,stopped taking food in regular quantity from past 1 month ...he became weak .we  consulted internal medicine doctor , suggest to do some test in that creatinine was 1.21 and other results were okay & after that in gap of month 1 month he again became weak , we did diabetes test with renal test - in that creatinine was 4.4 , urea 130 , blood urea 64.4 & uric acid 10.2 (all unuts mg/dl) came. doctor suggested to nephrologist ...now he is been admitted to hospital . what is the reason for this sudden changes in creatinine and other level in 20 days gap ? what is cure for this ? his health background - he had blood clot in heart hence 2  stents has been put in aug-2018 and he has controlled diabetes ...