What is the most appropriate initial radiologic investigation for diagnosing renal colic?

The non-contrast computed tomography (CT) scan is considered the most appropriate initial radiologic investigation for diagnosing renal colic due to its high sensitivity and specificity in detecting urinary calculi (kidney stones). The non-contrast CT scan provides excellent detail and can visualize stones of all sizes in different locations throughout the urinary tract, including the kidneys, ureters, and bladder. It does not require the use of contrast material, making it a rapid and effective imaging modality, especially useful in the acute setting of renal colic when patients may present with significant pain.

The use of ultrasound is often more limited; while it is superior for visualizing some aspects of kidney pathology, it may miss small stones or non-obstructing stones and is less sensitive than CT for diagnosing renal colic. X-rays can occasionally detect larger stones but are not a reliable initial investigation because many stones are radiolucent and will not be visible. MRI is generally not used for this purpose as it is more expensive and less readily available for acute evaluations compared to CT, and it is not as effective in visualizing urinary calculi.

Thus, for the most straightforward and clear assessment in acute cases of renal colic, a non-contrast CT scan stands out as the best