Hi, it is quite normal for the doctor to do all the necessary tests, before he makes a conclusive diagnosis. Besides, I am sure that he didn't want to worry you because some of the conditions that can cause enlarged kidney are very serious. I can mention some of them, but it does not mean that you suffer from any ones that I am aware of. Hydronephrosis is a medical term used to name enlarged kidneys. The kidney becomes enlarged because there is an obstruction of urine passage from the kidney. The source of the blockage can be a number of things. Kidney stones can cause these obstructions, but the pain related to this condition is usually very intense. Also a condition called polycystic kidney disease, in which cysts are formed inside the kidney, cause for the kidneys to look enlarged. And finally, kidney tumor cannot be passed by as a cause of enlarged kidney. I think that you should listen to your doctor and do all the necessary tests in order to determine the right cause of enlarged kidney in your case and the proper treatment.