Yes your uncle is having first stage of renal failure
and if adequate precautions are not taken, he shall fast progress to full blown renal failure.
You sholud get is USG
KUB done and rule out any obstructive cause.
If is hypertensive or diabetic then either of conditions need to be treated very well.
Cut down on his protein and see a nephrologist
for further attention. it is very important; a stitch
in time shall certainly save nine