Usually, simple cysts do not cause symptoms. Most often, these cysts are found when a person has an ultrasound or CT scan of the abdomen for some other reason. The radiologist's report would mention the presence of one or more cysts.
Simple cysts may develop when fluid from the urinary space leaks into the tissues of the kidney. Sometimes more than one cyst is seen in each kidney. (And they may vary in size.) Unless a simple cyst becomes very large, there is rarely any damage to the kidney.
To be certain that there is no other problem with the kidneys, your doctor may send you for a creatinine blood test and a urine test. The blood test is used to make you're your kidneys are functioning normally. The urine test, called a urinalysis, will detect any abnormal cells or proteins that could mean there is some kidney problem. If the blood and urine tests are normal, you won't need any other tests.
You want to be sure that you do have a simple cyst and not a "complex" cyst. Complex cysts contain some irregularity in appearance. They may contain blood or other material that might indicate a more serious problem. A person with a complex cyst needs to have a repeat CT scan or ultrasound in a few months. Or your doctor may refer you to a specialist for a potential biopsy.