From the Guidelines
Heavy calcium oxalate stones can be detected by ultrasound (US) with variable performance, but the addition of color Doppler and assessment of twinkling artifact can improve sensitivity, particularly for small renal stones. The detection of renal calculi using US demonstrates an overall sensitivity of 24% to 57% for stone detection, with decreased sensitivity for smaller stones 1. However, the combination of US and radiography can improve stone detection, yielding a sensitivity of 90% and specificity of 68%, although detection rates are decreased for stones <5 mm 1.
When it comes to the implications of heavy calcium oxalate on ultrasound, some key points to consider include:
- US has been found to be up to 100% sensitive and 90% specific for the diagnosis of ureteral obstruction (hydronephrosis, ureterectasis, and perinephric fluid) in patients presenting with acute flank pain 1
- The lack of hydronephrosis on US makes the presence of a larger ureteral stone (>5 mm) less likely 1
- The addition of color Doppler and assessment of twinkling artifact can provide higher sensitivity, particularly for small renal stones, with described sensitivity reported as high as 99% for stones <5 mm in patients with lumbar pain or history of renal stones 1
In terms of management, it is essential to consider the following:
- Increased fluid intake to dilute urine and prevent crystal formation
- Dietary modifications, including reducing oxalate-rich foods and limiting sodium intake
- Moderate calcium consumption from dietary sources to bind to oxalate in the gut
- Medications such as potassium citrate and thiazide diuretics to reduce urinary calcium excretion and increase urine pH
Overall, the use of US, combined with clinical evaluation and other diagnostic tools, can help diagnose and manage heavy calcium oxalate stones, improving patient outcomes and reducing the risk of recurrence. Regular follow-up with urinalysis and imaging is crucial to monitor treatment effectiveness and prevent recurrence 1.
From the Research
Implications of Heavy Calcium Oxalate on Ultrasound
- The formation of calcium oxalate stones depends on the state of urinary supersaturation with respect to calcium and oxalate, and the action of urinary inhibitors of crystal nucleation, aggregation, and growth 2.
- Idiopathic hypercalciuria is the most common cause of calcium oxalate stones, characterized by hypercalciuria, normocalcemia, and intestinal calcium hyperabsorption with or without elevated serum 1,25(OH)2D3 levels 2.
- Current diagnostic evaluation of recurrent calcium oxalate nephrolithiasis includes analysis of stone composition, measurement of serum calcium, phosphate, uric acid, and creatinine, and 24-hour urine collection for analysis of volume, pH, and excretion of calcium, phosphorus, magnesium, uric acid, citrate, sodium, oxalate, and creatinine 2.
- Therapy to prevent stone recurrence is designed to reduce urinary supersaturation of calcium oxalate by increasing urine volume, reducing urine calcium, maintaining dietary calcium intake, and adding potassium citrate if urine citrate levels are reduced 2.
- Dietary oxalate restriction can reduce urine oxalate excretion if it is elevated 2.
- Increasing dietary calcium intake may actually reduce the risk of calcium oxalate stone formation, as it can bind to intestinal oxalate and reduce its absorption 3, 4, 5.
- The effect of increasing dietary oxalate on urinary calcium oxalate supersaturation is difficult to predict, but studies have shown that it can decrease calcium oxalate supersaturation due to the decrease in urinary calcium offsetting the increase in urinary oxalate 6.
- The dependence of oxalate absorption on daily calcium intake has been investigated, and it has been found that oxalate absorption depends linearly on calcium intake within a certain range 5.