What is the diagnostic test of choice for polycystic kidney disease?

The most appropriate diagnostic test for polycystic kidney disease (PKD) is ultrasound. This imaging modality is highly effective in identifying renal cysts, which are characteristic of PKD. Ultrasound is non-invasive, does not involve radiation exposure, and allows for the assessment of the number, size, and distribution of cysts within the kidneys.

In the case of suspected autosomal dominant polycystic kidney disease (ADPKD), ultrasound can help visualize cysts in individuals with a family history, especially in children and young adults. Additionally, it can be used to monitor disease progression over time.

While other imaging techniques such as CT scans and MRIs can also detect renal cysts and may provide more detailed information, they are generally not the first-line approach due to their higher cost, increased complexity, and exposure to radiation in the case of CT scans. X-rays are not useful for this condition since they cannot adequately visualize soft tissue structures like the kidneys or their cysts. Therefore, ultrasound remains the preferred and most effective initial diagnostic tool for identifying polycystic kidney disease.