Kidney stones: How to reduce the risk for recurrence

Clinical pearls for frontline PCPs

A 55-year-old man new to the area presents to the ED complaining of excruciating left flank pain that radiates into his scrotum. He noted blood in the urine this morning and became worried enough to seek emergency care.

The patient just got back from a long fishing trip and wonders if his low fluid intake contributed to his feeling poorly. In retrospect, he thinks that he has had similar episodes in the past but never associated them with this much pain. About 5 years ago, he had a small amount of blood in the urine with one of the painful episodes.

In the ED, he was given IV fluids and IV ketorolac for the pain, which helped. A kidney, ureter and bladder (KUB) X-ray showed a hyper density in the area between his left kidney and bladder. A urinalysis (UA) showed more than 100 red blood cells per high power field (RBCs/HPF). A CT of the abdomen/pelvis showed a 5 mm stone in the distal 1/3 of the left ureter. He was sent out on tamsulosin 4 mg daily and was asked to follow up with a local primary care provider. He was advised to increase his fluid intake and was given a strainer for his urine.

Philip A. Bain

At the PCP visit, the patient brought in what he thought was a stone fragment found in the strainer, and the PCP sent it for stone analysis. His pain had completely resolved. His PCP explained why kidney stones form and what can be done to reduce the risk for recurrent stone formation. The PCP thought that his previous episodes were also likely due to nephrolithiasis. The patient was given a handout on kidney stones and asked to increase his fluid intake enough to make 2.5 L of urine per day at minimum. In addition, the patient was sent to the lab to get a urine jug to collect a 24-hour sample for analysis of pH, urine volume and saturation indices for calcium, uric acid and oxalate. A follow-up KUB showed no evidence of the left ureteral stone that was noted previously.

In about a week, the stone results returned as 80% calcium oxalate and 20% calcium phosphate. The supersaturation risk profile was notable for a volume of 2,500 mL, a pH of 6.2 and urine supersaturated with calcium.

The patient’s PCP reviewed the pros and cons of treatment, as well as the significantly increased risk for another stone forming in the next 5 to 10 years. After a shared decision-making discussion, the patient was started on 25 mg of hydrochlorothiazide to reduce the hypercalciuria (and lower his BP that was mildly elevated in the office).

The patient was followed by his PCP, only seeing him for his annual physical exam for the next 5 years. The patient did not have any further episodes of nephrolithiasis.

Lessons learned:

1. Kidney stones are the most common condition affecting the genitourinary system, and the prevalence has increased in the past decade. Twelve percent of the world’s population have had kidney stones.
2. There are many types of kidney stones. By far, the most common are calcium stones (80%). Others include uric acid, struvite and cysteine. Patients can have more than one type of stone.
3. Having had one kidney stone is a major risk factor for subsequent stones — 15% within the first year and 50% within the next 10 years.
4. Increased oxalate absorption in the small intestine (usually due to malabsorption or gastric bypass surgery) can lead to calcium oxalate stones.
5. Dehydration is the primary risk factor for stone formation. Stone formers should drink at least 2.5 L of water per day and make at least 2.5 L of urine per day. They should purchase a Nalgene-like water bottle to measure their urine output.
6. Kidney stones form because of urine supersaturation causing solutes to precipitate. The goal is to prevent supersaturation.
7. Patients with renal colic often present with severe flank pain (but this can present more vaguely in older adults). The severe pain can be accompanied by nausea/vomiting and gross hematuria. If obstruction occurs, pyelonephritis can occur. Painless microscopic hematuria can occur if stones are embedded in the kidney. 
8. Diagnosis involves symptoms, UA, urine pH, basic metabolic panel and KUB X-ray, although some stones are not seen on X-ray (eg, uric acid stones). Patients should strain urine for stone fragments and bring them in for analysis. Twenty-four-hour urine studies for volume, pH and supersaturation can be very helpful as well.
9. Treatment of the acute episode includes parenteral NSAIDs and increased fluid intake. Alpha blockers like tamsulosin reduce ureteral smooth muscle spasm and may help stone passage, especially if they are 5 to 10 mm in size. Stones larger than 6 mm may need a urology consult for removal.
10. To reduce the risk for future stones, the patient should increase fluids, limit salt in diets to less than 2,000 mg per day and decrease animal protein intake (less than 8 oz/day of beef, pork, poultry and fish). Medications like thiazide diuretics, allopurinol and/or citric acid can help if supersaturation studies are suggestive. A recent study by Dhayat and colleagues has called into question whether hydrochlorothiazide (HCTZ) actually reduces the risk for recurrent kidney stones. Although this is a single study, if replicated, the use of HCTZ may fall out of favor, leaving allopurinol and citrates as the primary medications to reduce stone recurrence.

References:

• Bhojani N, et al. Can Urol Assoc J. 2022;doi:10.5489/cuaj.7872.
• Dhayat, NA, et al. N Engl J Med. 2023;doi:10.1056/NEJMoa2209275.
• Kidney stones: Treatment and prevention. https://www.aafp.org/pubs/afp/issues/2019/0415/p490.html. Published April 15, 2019. Accessed Jan. 11, 2024.
• Medical management of kidney stones. https://www.auanet.org/guidelines-and-quality/guidelines/kidney-stones-medical-mangement-guideline. Accessed Jan. 11, 2024.
• Mksap review questions on kidney stones. Published Feb. 28, 2019. Accessed Jan. 11, 2024. https://www.slideshare.net/vmimr/mksap-review-2-2619-kidney-stones.