This is a medical question of type : exams and tests 
 How to diagnose Wilms Tumor and Other Childhood Kidney Tumors ? 
 Tests are used to screen for Wilms tumor.
                    Screening tests are done in children with an increased risk of Wilms tumor. These tests may help find cancer early and decrease the chance of dying from cancer.   In general, children with an increased risk of Wilms tumor should be screened for Wilms tumor every three months until they are at least 8 years old. An ultrasound test of the abdomen is usually used for screening. Small Wilms tumors may be found and removed before symptoms occur.    Children with Beckwith-Wiedemann syndrome or hemihyperplasia are also screened for liver and adrenal tumors that are linked to these genetic syndromes. A test to check the alpha-fetoprotein (AFP) level in the blood and an ultrasound of the abdomen are done until the child is 4 years old. An ultrasound of the kidneys is done after the child is 4 years old. In children with certain gene changes, a different schedule for ultrasound of the abdomen may be used.   Children with aniridia and a certain gene change are screened for Wilms tumor every three months until they are 8 years old. An ultrasound test of the abdomen is used for screening.   Some children develop Wilms tumor in both kidneys. These often appear when Wilms tumor is first diagnosed, but Wilms tumor may also occur in the second kidney after the child is successfully treated for Wilms tumor in one kidney. Children with an increased risk of a second Wilms tumor in the other kidney should be screened for Wilms tumor every three months for up to eight years. An ultrasound test of the abdomen may be used for screening.
                
                
                    Tests that examine the kidney and the blood are used to detect (find) and diagnose Wilms tumor and other childhood kidney tumors.
                    The following tests and procedures may be used:         -   Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patients health habits and past illnesses and treatments will also be taken.    -   Complete blood count (CBC): A procedure in which a sample of blood is drawn and checked for the following:               - The number of red blood cells, white blood cells, and platelets.      - The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.      - The portion of the blood sample made up of red blood cells.             -   Blood chemistry studies : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease. This test is done to check how well the liver and kidneys are working.    -   Renal function test : A procedure in which blood or urine samples are checked to measure the amounts of certain substances released into the blood or urine by the kidneys. A higher or lower than normal amount of a substance can be a sign that the kidneys are not working as they should.    -   Urinalysis : A test to check the color of urine and its contents, such as sugar, protein, blood, and bacteria.    -  Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram. An ultrasound of the abdomen is done to diagnose a kidney tumor.    -   CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, such as the chest, abdomen, and pelvis, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye is injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.    -  MRI (magnetic resonance imaging) with gadolinium: A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body, such as the abdomen. A substance called gadolinium is injected into a vein. The gadolinium collects around the cancer cells so they show up brighter in the picture. This procedure is also called nuclear magnetic resonance imaging (NMRI).     -  X-ray: An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body, such as the chest and abdomen.    -   PET-CT scan : A procedure that combines the pictures from a positron emission tomography (PET) scan and a computed tomography (CT) scan. The PET and CT scans are done at the same time on the same machine. The pictures from both scans are combined to make a more detailed picture than either test would make by itself. A PET scan is a procedure to find malignant tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. The PET scanner rotates around the body and makes a picture of where glucose is being used in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose than normal cells do.    -   Biopsy : The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer. The decision of whether to do a biopsy is based on the following:                - The size of the tumor.      - The stage of the cancer.      - Whether cancer is in one or both kidneys.      - Whether imaging tests clearly show the cancer.      - Whether the tumor can be removed by surgery.      - Whether the patient is in a clinical trial.         A biopsy may be done before any treatment is given, after chemotherapy to shrink the tumor, or after surgery to remove the tumor.