From the Guidelines
The most appropriate next step would be to order a parathyroid hormone (PTH) level test. This patient has hypercalcemia (calcium level of 10.5 mg/dL with elevated ionized calcium) and recurrent calcium oxalate stones, which strongly suggests primary hyperparathyroidism as the underlying cause, as indicated by the American Urological Association guideline 1. Primary hyperparathyroidism is characterized by excessive PTH secretion, typically from a parathyroid adenoma, leading to increased serum calcium levels and recurrent stone formation. The patient's age (60 years) and female gender also fit the typical demographic for primary hyperparathyroidism. The recurrent nature of her stone disease (three episodes in five years) indicates a metabolic abnormality rather than random stone formation.
Key Considerations
- The patient's hypercalcemia and recurrent calcium oxalate stones suggest primary hyperparathyroidism as the underlying cause, which is supported by the guideline recommendation to obtain serum intact parathyroid hormone level as part of the screening evaluation if primary hyperparathyroidism is suspected 1.
- The American College of Physicians guideline also recommends management with increased fluid intake and pharmacologic monotherapy with a thiazide diuretic, citrate, or allopurinol to prevent recurrent nephrolithiasis, but these measures are secondary to addressing the potential underlying primary hyperparathyroidism 1.
- If the PTH level is elevated or inappropriately normal in the setting of hypercalcemia, referral to an endocrinologist or surgeon would be warranted for consideration of parathyroidectomy, which would address both the hypercalcemia and reduce the risk of future stone formation.
- Additional metabolic evaluation including 24-hour urine collection for stone risk factors could be considered after addressing the likely primary hyperparathyroidism, as recommended by the American Urological Association guideline 1.
From the FDA Drug Label
In all groups, treatment that included Potassium Citrate was associated with a sustained increase in urinary citrate excretion from subnormal values to normal values (400 to 700 mg/day), and a sustained increase in urinary pH from 5.6-6.0 to approximately 6. 5. The stone formation rate was reduced in all groups as shown in Table 1. Table 1. Effect of Potassium Citrate In Patients With Calcium Oxalate Nephrolithiasis. Remission defined as “the percentage of patients remaining free of newly formed stones during treatment”. GroupBaselineOn TreatmentRemissionAny Decrease I (n=19)12 ± 300.9 ± 1.358%95% II (n=37)1.2 ± 20.4 ± 1. 589%97% III (n=15)4.2 ± 70.7 ± 267%100% IV (n=18)3.4 ± 80.5 ± 294%100% Total (n=89)4.3 ±150.6 ± 280%98%
The most appropriate test to order next would be Potassium Citrate (PO) 2, as it has been shown to reduce the stone formation rate in patients with calcium oxalate nephrolithiasis. Key benefits of Potassium Citrate include:
- Increased urinary citrate excretion
- Increased urinary pH
- Reduced stone formation rate Given the patient's history of ureterolithiasis with calcium oxalate stones, Potassium Citrate is a suitable treatment option to consider.
From the Research
Next Steps for Patient with Recurrent Ureterolithiasis
- The patient has a history of recurrent ureterolithiasis, with previous stone analysis showing calcium oxalate stones 3.
- Given the patient's elevated calcium level and ionized calcium level, as well as the presence of calcium oxalate stones, it is essential to investigate the underlying causes of stone formation.
- The study by 3 highlights the importance of considering both "classic" risk factors (such as hypercalciuria, hyperoxaluria, hypocitraturia, hyperuricosuria, and hypomagnesuria) and "new" risk factors (including overweight, hypertension, and a lack of oxalate-degrading bacteria in the gut) in the formation of calcium oxalate stones.
- To further evaluate the patient's condition, it would be appropriate to order:
- A 24-hour urine collection to assess for hypercalciuria, hyperoxaluria, and other biochemical abnormalities 3.
- Laboratory tests to evaluate the patient's serum and urine electrolyte levels, including calcium, oxalate, and uric acid 3.
- A review of the patient's dietary habits and lifestyle factors, including weight and blood pressure, to identify potential contributing factors to stone formation 3.