Which statement about diagnosing renal calculi is true?

The statement that a helical CT scan is highly sensitive and specific is correct. This imaging modality is widely recognized as the gold standard for diagnosing renal calculi because it can accurately detect stones regardless of their composition or size. Helical CT scans provide detailed cross-sectional images of the kidneys, ureters, and bladder, allowing for a precise evaluation of the urinary tract. This imaging technique does not require contrast, making it particularly advantageous in emergency settings where renal stones are suspected.

In contrast, other options do not reflect the same level of diagnostic reliability. For instance, urinalysis can suggest the presence of renal stones through findings such as hematuria, but it is not definitive for diagnosis on its own. The KUB (Kidneys, Ureters, Bladder) X-ray may miss a significant percentage of calculi, particularly smaller stones or those not radiopaque. Ultrasound may be more useful in certain scenarios, like in pregnant patients or those who need to avoid radiation, but it is not the primary imaging choice for small ureteral stones due to its lower sensitivity compared to CT. Thus, the helical CT's high sensitivity and specificity make it the preferred method for accurate renal calculus diagnosis.