Which diagnostic test is least invasive for a child with suspected Wilms tumor?

The least invasive diagnostic test for a child with suspected Wilms tumor is an abdominal ultrasound. This test is non-invasive and does not involve any radiation, making it particularly suitable for children. An abdominal ultrasound uses sound waves to create images of the organs and structures within the abdomen, allowing healthcare providers to assess the kidneys and detect any abnormalities such as tumors.

In cases of suspected Wilms tumor, an ultrasound is often the first step in imaging because it can quickly and safely provide preliminary information about the presence of a mass in the kidney. It is not only effective in identifying the tumor but also assists in evaluating its size and characteristics without subjecting the child to more complex procedures.

Other options like a renal biopsy are more invasive and involve taking tissue samples, which can pose risks and complications, especially in a child. CT scans and MRIs, while useful diagnostic tools, involve either radiation exposure (in the case of CT) or more complex procedures to perform (for MRI, which may require sedation in young children). These tests, while valuable for further characterization and staging of the tumor, are not the least invasive approach for initial assessment.