From the Guidelines

Noncontrast CT of the abdomen and pelvis is the best test for nephrolithiasis.

Noncontrast CT has a high sensitivity of 97% for detecting renal calculi, making it the reference standard for evaluating urolithiasis 1.
The use of low-dose noncontrast CT can minimize patient radiation dose while maintaining a high diagnostic performance, with a pooled sensitivity of 97% and specificity of 95% 1.
Noncontrast CT allows for accurate assessment of stone size and location, which is important in planning urologic management 1.
Other imaging modalities, such as ultrasound and abdominal radiography, have lower sensitivities and are not recommended as first-line tests for nephrolithiasis 1.
CT abdomen and pelvis with IV contrast is not recommended as a first-line test, as the presence of contrast may obscure stones within the renal collecting system 1.

Low-dose CT has been shown to be comparable to standard-dose CT in visualizing hydronephrosis and diagnosing alternative diseases, but may have lower sensitivity for detecting small stones (<2 mm) 1.
The use of digital tomosynthesis (DT) and MR urography (MRU) may be considered in certain cases, but are not widely available and have limited evidence supporting their use as first-line tests for nephrolithiasis 1.

From the Research

The best test for nephrolithiasis is a topic of ongoing debate, with various studies suggesting different imaging modalities as the most effective diagnostic tool 2, 3.
Noncontrast computed tomography (CT) of the abdomen and pelvis is consistently considered the most accurate diagnosis, but it exposes patients to ionizing radiation 3.
Ultrasonography (US) has a lower sensitivity and specificity than CT, but does not require radiation, making it a potentially useful initial imaging modality 2, 3.
The sensitivity and specificity of US for detecting renal calculi are 54% and 91%, respectively, with a significant association between sensitivity and stone size 2.

A study comparing US and CT found that US had a lower sensitivity, but the combination of US and plain abdominal film of kidney, ureter, and bladder (KUB) increased sensitivity to 78% 2.
However, even with the combination of US and KUB, 37% of patients may still be inappropriately counseled to undergo observation 2.
MRI provides the possibility of 3D imaging without radiation, but it is costly and currently has limitations in visualizing stones 3.

Biochemical evaluation is an essential part of managing nephrolithiasis, focusing on urinary excretion of promoters and inhibitors of stone formation, as well as systemic diseases potentially related to secondary nephrolithiasis 4, 5.
Metabolic evaluation can help identify underlying causes of stone formation and guide preventive measures, such as dietary changes, thiazide diuretics, and other medications 4, 5, 6.
High fluid intake is a mainstay of prevention, and metabolic evaluation can indicate other appropriate preventive measures 6.