What is the risk of nephrolithiasis in a postmenopausal woman taking calcium supplements?

From the Guidelines

For a 57-year-old postmenopausal woman with recurrent kidney stones who is taking calcium supplements, I recommend discontinuing her current calcium supplements and limiting her daily calcium intake to 1000-1200 mg total (including dietary sources) to minimize the risk of nephrolithiasis, as suggested by 1. To manage her osteoporosis risk, she should increase her dietary calcium intake and consider alternative supplementation options.

• Increase fluid intake to at least 2-2.5 liters daily to dilute stone-forming substances in urine.
• Reduce sodium intake to less than 2300 mg daily and moderate animal protein consumption to decrease urinary calcium excretion.
• A 24-hour urine collection should be performed to identify specific stone risk factors.
• If she has calcium oxalate stones, limit high-oxalate foods like spinach, rhubarb, and nuts. The evidence from 1 and 1 suggests that calcium supplementation may increase the risk of nephrolithiasis, and therefore, it is crucial to weigh the benefits of calcium supplementation against the potential risks in this patient.
• Thiazide diuretics like hydrochlorothiazide 12.5-25 mg daily may be prescribed if hypercalciuria is detected. It is essential to note that the patient's current calcium intake is substantially greater than the recommended daily intake, and reducing her supplementation can help minimize the risk of kidney stones while still maintaining adequate calcium levels for bone health, as recommended by 1.

From the Research

Patient Profile

• A 57-year-old post-menopausal woman
• Passed her second kidney stone in 1 year
• Taking calcium supplements to prevent osteoporosis

Kidney Stone Formation

• Calcium oxalate nephrolithiasis is a common syndrome that recurs and may be complicated by infection, obstruction, bleeding, and rarely, impairment in renal function 2
• The formation of Ca oxalate stones depends on the state of urinary supersaturation with respect to Ca and oxalate and the action of urinary inhibitors of crystal nucleation, aggregation, and growth 2
• Idiopathic hypercalciuria is the most common cause of Ca oxalate stones and is characterized by hypercalciuria, normocalcemia, and intestinal Ca hyperabsorption with or without elevated serum 1,25(OH)2D3 levels in the absence of other known causes of hypercalciuria 2, 3

Diagnostic Evaluation

• Current diagnostic evaluation of recurrent Ca oxalate nephrolithiasis should be conducted while the patients follow their usual diets and includes the analysis of stone composition, measurement of serum Ca, phosphate, uric acid, 1,25(OH)2D3, and creatinine, and 24-hour urine collection for an analysis of volume, pH, and excretion of Ca, phosphorus, magnesium, uric acid, citrate, sodium, oxalate, and creatinine 2
• A noncontrast helical computed tomography scan of the abdomen is the diagnostic procedure of choice for detection of small and radiolucent kidney stones with sensitivity and specificity of nearly 100% 3

Treatment and Prevention

• Therapy to prevent stone recurrence is designed to reduce urinary supersaturation of Ca oxalate by increasing urine volume, reducing urine Ca to below 200 mg/24 hr with thiazide, maintaining dietary Ca intake at 600 to 800 mg/day, and adding potassium citrate if urine citrate levels are reduced 2
• Calcium supplementation may increase the risk of stone formation, especially if taken in large doses or separate from a meal 4
• Potassium citrate can be used for medical prophylaxis of Ca-Ox stone patients with hypercalciuria, with efficacy comparable to hydrochlorothiazide treatment 5
• Calcium supplements in the treatment of osteoporosis alone or in combination with another type of treatment do not significantly increase the risk of nephrolithiasis or renal colic 6

Recommendations

• The patient should undergo a complete metabolic workup to identify the risk factors for stone formation 3
• The patient should be educated on strategies to prevent kidney stone recurrence, including a dietary regimen low in salt and protein, rich in calcium and magnesium, and adequate fluid intake 3
• The patient's calcium supplementation should be monitored, and the dose adjusted as necessary to minimize the risk of stone formation 4, 6