My grandpa had contrast ct and his kidney function went down, he is now in the hospital overnight? should i be worried??

Is this a new complication In a healthy person, a complication in a person with high risk diseases such as diabetes or a complication of preexisting kidney disease? These factors play a great role in the prognosis of full recovery of kidney function. Your physician & specialists involved in his care are more qualified to answer your question.

If the issue is contrast induced nephropathy there is a good chance it will respond to iv fluids. Otherwise, the medical team remains your best resource for further clarification.