After a motor vehicle crash, which diagnostic test is most appropriate for a patient with symptoms of hematuria?

In the context of a patient presenting with hematuria following a motor vehicle crash, a CT scan of the abdomen and pelvis is the most appropriate diagnostic test. This imaging modality allows for a comprehensive evaluation of the abdominal and pelvic organs, which can help identify injuries to the kidneys, bladder, and other urinary tract structures that may not be visible through other means. Given the high sensitivity of CT imaging in detecting solid organ injuries, including renal lacerations or contusions, it is crucial for assessing potential complications arising from trauma.

The other options are less suitable in this scenario. Retrograde urethrography is primarily used to assess injuries to the urethra, which is not the primary concern in the setting of hematuria after abdominal trauma. Serum haptoglobin is mainly used to evaluate hemolytic anemia, which would not directly address the source of hematuria. Urine myoglobin can indicate muscle injury or rhabdomyolysis, but it does not provide the necessary information regarding potential urinary tract injuries resulting from the crash. Therefore, the CT scan stands out as the optimal choice to evaluate the hematuria and associated abdominal trauma.