From the Guidelines
For the evaluation of renal stones, I recommend starting with a comprehensive assessment including urinalysis, serum chemistry panel, and imaging studies, with the preferred initial imaging being a non-contrast CT scan of the abdomen and pelvis, as it has a high sensitivity of 97% for detecting stones, as reported in the most recent study 1. The evaluation of renal stones should prioritize a thorough assessment to identify the stone composition, underlying metabolic disorders, and to guide prevention strategies.
- Key components of the evaluation include: + Urinalysis to check for blood, protein, and infection + Serum chemistry panel (calcium, phosphorus, uric acid, creatinine, BUN) to identify metabolic abnormalities + Imaging studies, with non-contrast CT scan of the abdomen and pelvis being the preferred initial imaging due to its high sensitivity and ability to accurately detect even small stones, as well as visualize secondary signs of urolithiasis and complications 1 + Additional blood tests, such as PTH levels, and 24-hour urine collection for calcium, oxalate, citrate, uric acid, sodium, and creatinine to identify underlying metabolic disorders
- Stone analysis is crucial if a stone is passed or retrieved surgically to guide prevention strategies, and patients should be instructed to strain their urine to catch any passed stones for analysis.
- Hydration is essential during the evaluation period, with a recommendation of 2-3 liters of fluid daily, and pain management may include NSAIDs like ibuprofen (600-800mg every 6-8 hours) or, if needed, short-term opioid analgesics.
- Medical expulsive therapy with tamsulosin 0.4mg daily may be considered for stones <10mm in the distal ureter, as part of a comprehensive approach to reduce recurrence rates, which can be as high as 50% within 5 years without appropriate intervention, as noted in previous guidelines 2.
From the Research
Evaluation of Renal Stones
The evaluation of renal stones involves various imaging techniques, including computed tomography (CT) scans, ultrasonography, and kidney, ureter, and bladder radiographs.
- CT scans are highly sensitive for detecting kidney stones and provide valuable information regarding stone size, composition, location, and overall stone burden 3.
- However, CT scans can be deceiving, and motion artifact in CT images can cause a warping distortion effect that makes renal stones appear larger than they actually are 3.
- Ultrasonography is also a useful imaging technique for evaluating renal stones, particularly in patients with suspected renal colic, and can help reduce radiation exposure 4, 5.
- Non-contrast CT (NCCT) is a standard imaging study in the emergency department diagnosis of nephro- and ureterolithiasis, and can help identify renal or ureteral calculi, as well as unexpected intra-abdominal pathology 6.
Imaging Techniques
Different imaging techniques are recommended for different clinical scenarios:
- CT is recommended in certain scenarios, such as when the diagnosis of kidney stone is suspected and the patient has a high risk of alternative diagnoses 4.
- Ultrasonography is recommended in scenarios where the risk of alternative diagnoses is low, such as in younger patients with uncomplicated suspected renal colic 4, 5.
- Ultra-low-dose limited renal CT is a novel approach that uses volumetric analysis for renal stone surveillance, and has advantages over standard unenhanced CT, including lower radiation dose and cost 7.
Clinical Considerations
Clinical considerations, such as patient age, symptoms, and medical history, play an important role in determining the appropriate imaging technique for evaluating renal stones:
- Younger patients with uncomplicated suspected renal colic are unlikely to have dangerous alternative diagnoses or need emergent intervention, and may not require immediate CT scans 5.
- Patients with a history of kidney stones or other underlying medical conditions may require more frequent or detailed imaging studies to monitor their condition 3, 7.