From the Guidelines
Patients with suspected kidney stones should undergo a non-contrast CT scan of the abdomen and pelvis as the initial imaging study, as it is the most appropriate and sensitive test for detecting stones, according to the most recent guidelines from the American College of Radiology 1. When evaluating patients with kidney stones, a comprehensive approach is necessary to ensure proper diagnosis, treatment planning, and prevention of recurrence. This includes:
- Medical history and physical examination to identify underlying medical conditions and dietary habits that may contribute to stone formation
- Urinalysis to check for blood, pH, crystals, and signs of infection, as well as urine culture if infection is suspected 1
- Blood tests, including serum creatinine, electrolytes, calcium, phosphorus, and uric acid, to assess kidney function and identify metabolic abnormalities
- Imaging studies, with non-contrast CT scan being the gold standard for detecting stones, especially in patients with acute onset flank pain and suspicion of stone disease 1
- Ultrasound may be used as an alternative, especially in pregnant patients or children, to avoid radiation exposure
- For recurrent stone formers, a 24-hour urine collection is recommended to measure volume, calcium, oxalate, citrate, sodium, uric acid, and creatinine, helping identify specific metabolic abnormalities driving stone formation
- Stone analysis should be performed when possible to determine composition, which guides prevention strategies The use of MRU without IV contrast or CT abdomen and pelvis without IV contrast may be appropriate, as stated by Gupta et al, in certain cases, but the most recent guidelines from the American College of Radiology recommend non-contrast CT scan as the initial imaging study 1.
From the Research
Kidney Stone Patient Exams
- Kidney stone patient exams often involve imaging modalities such as non-contrast CT scans, which are becoming the standard for urinary stone disease diagnosis and follow-up 2.
- The use of low-dose and ultra-low-dose CT protocols can help reduce radiation exposure, while still maintaining high diagnostic accuracy 3.
- Studies have shown that ultra-low-dose CT scans can detect all types of kidney stones, except for small uric acid fragments, which may require higher energy settings 2.
- Non-contrast CT scans are recommended for initial evaluation and diagnosis of kidney stones, as they can provide detailed images of the stones and surrounding tissue 4, 5.
Imaging Modalities
- Non-contrast CT scans are the preferred imaging modality for kidney stone diagnosis and follow-up, due to their high sensitivity and specificity 2, 3.
- Ultrasound is recommended as the initial imaging modality for suspected renal colic in pregnant women and children, but low-dose CT scans may also be safe in pregnancy 5.
- Plain radiography is suggested for follow-up of radiopaque stones, while ultrasound and limited IVU are reserved for follow-up of radiolucent stones to minimize cumulative radiation exposure 5.
Stone Composition and Detection
- The composition of kidney stones can affect their detection on CT scans, with calcium-based stones having a higher Hounsfield unit (HU) value than non-calcium-based stones 2.
- The HU value of renal papilla can be a useful predictor of recurrence of stone disease, with higher HU values indicating a higher risk of recurrence 6.
- Ultra-low-dose CT scans can detect all types of kidney stones, except for small uric acid fragments, which may require higher energy settings 2.