A 65-year-old woman presents to urgent care with sudden-onset severe right flank pain that began 6 hours ago. The pain radiates to her right lower abdomen and groin. She describes the pain as sharp, intermittent, and unrelenting. She also reports some nausea but no vomiting. She denies fever, chills, or dysuria. She has no family history of kidney stones. She suffers from hypertension and has been diagnosed with osteoporosis. She takes hydrochlorothiazide 25 mg daily and a 1200 mg daily calcium supplement. She reports no alcohol or tobacco use and enjoys at least 2 cups of tea per day.
On physical examination, her blood pressure is 150/88 mm Hg, heart rate is 90 beats/min, and temperature is 98.4˚F; she has normal bowel sounds, tenderness to palpation in the right flank, and no rebound or guarding. Diagnostic studies include urinalysis, which shows microscopic hematuria, and point-of-care ultrasound, which indicates hydronephrosis. Which of the following factors is most likely to have contributed to this patient’s kidney stone formation?
- Excessive sodium intake
- Long-term hydrochlorothiazide use and calcium supplementation
- Chronic dehydration
- High oxalate intake from tea consumption
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Answer: b. While thiazide diuretics are used to reduce urinary calcium excretion in patients prone to stones, paradoxically, long-term use in combination with calcium supplementation can increase calcium levels, leading to calcium-based kidney stones (eg, calcium oxalate or calcium phosphate). Excessive calcium supplementation paired with inadequate fluid intake can also increase the risk of calcium stone formation. This case highlights the importance of reviewing medication history in older patients with kidney stones. Long-term thiazide diuretics combined with calcium supplementation can contribute to stone formation, especially in the setting of insufficient hydration.
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Tracey Davidoff, MD, FACP, FCUCM, has practiced Urgent Care Medicine for more than 15 years. She is Board Certified in Internal Medicine. Dr. Davidoff is a member of the Board of Directors of the Urgent Care Association and serves as Co-Editor-in-Chief of the College of Urgent Care Medicine’s “Urgent Caring” publication. She is also the Vice President of the Southeast Regional Urgent Care Association and a member of the editorial board of the Journal of Urgent Care Medicine. At EB Medicine, Dr Davidoff is Editor-In-Chief of Evidence-Based Urgent Care, and co-host of the Urgentology podcast.
