Wow ! It is sure good to see how well you are doing, considering your condition only a short time ago.
Jim
So sorry to hear about your Dad. They tested his kidney prior to the cath due to the contrast dye, or that is one major reason for the test. He is diabetic and it seems he was having a tad of kidney trouble prior to the surgery (kidney function test).
The contrast dye used for imaging during the cath, is hard on the kidneys. Afterward they really flush the kidneys with IV solution to clear the dye from the system/kidneys. Check and see if they used the more gentle type of dye, as they should have, since your Dad was diabetic and barely passed the kidney function test. This type of dye is expensive and they do not like to use it, I don't think, because of insurance companies (shame).
During the surgery, your Dad was placed on a heart lung bypass machine. This was probably another insult to your Dad's kidneys.
He needs to be elevated in bed, so he can clear his lungs. This will help prevent pneumonia.
My best to you and your Dad,
Jack