Doctors generally use imaging tests, such as CT scans, MRIs or ultrasounds, to closely examine kidney cysts, explains the National Institutes of Health. From these tests, doctors can determine if the growth is a simple kidney cyst or a more serious condition, such as a malignant tumor.
A kidney function test, which involves testing a sample of the patient's blood, can also determine whether the cyst impairs the function of the kidneys, notes Mayo Clinic. Cysts are fluid-filled sacs that are usually benign, explains Medical News Today. If a doctor determines that a cyst is cancerous, he may suggest surgical removal.