GFR is less than 70. By blood test?

Recently he had an problem where not getting urine properly and also no pain.Creatinine level is .88-1.2 checked in different labs for repeatability. After consulting with two different nephrology doctor we had confusion where one suggests normal kidney function and other 20% kidney damage with suggestion of renosave medicine.We would like to know whether we need to go for any medicine to prevent further kidney damage or we need to monitor eGFR to see any abnormality by Creatinine level by blood test? Also as per doctor suggestion DTPA Test is conducted to examine the kidney function and following are the test report comments, 1.There is abnormally increased circulating background tracer noted (suggestive of renal parenchymal dysfunction). 2.Bilateral Subnormally functioning kidneys without obstruction. Low normal limit of GFR for Age>70ml/min Kindly clarify us and Also suggest us we need to take preventive medicine in this case or not to avoid any sort of kidney damag