Kidney stones are a common, “bread and butter” condition encountered by nephrologists in clinical practice. In the United States, up to 16% of men and 8% of women will have at least one symptomatic stone episode by the age of 70 years. Furthermore, the association between kidney stones and other systemic abnormalities needs to be recognized.
It is commonly recognized that “a stone is not necessarily the disease” but rather a “symptom” of an underlying abnormality (think: hyperuricosuria, hypercalciuria, hyperoxaluria, etc.). Therefore, even if the initial stone is spontaneously expelled or surgically removed, it does not make the underlying abnormality go away. It is for this reason that risk of stone recurrence after an initial episode of nephrolithiasis is extremely high, approaching 50% within 10 years.
Pfau and Knauf have provided an updated Core Curriculum article (freely available) for AJKD on the topic of nephrolithiasis. Let’s test what you know about kidney stones. If you stumble on anything, go back to this very comprehensive review, which has detailed explanations to all these questions!
1. Which of the following is NOT a recognized risk factor for kidney stone formation?
Low fluid intake
High calcium diet
Correct! High dietary calcium intake is independently associated with lower risk of kidney stones. This is because calcium binds to intestinal oxalate, therefore reducing the amount of soluble oxalate available for absorption. Low fluid intake, high salt and protein diet, and geographic variations are known risk factors for kidney stones.
Residence in certain parts of the United States, including the Carolinas, Georgia, and Alabama
High animal protein intake
2. Which of the following medications should NOT increase the risk of kidney stone formation?
Correct! Hydrochlorothiazide, while a diuretic, also reduces hypercalciuria. This occurs as inhibition of the sodium chloride co-transporter in the distal tubule leads to volume depletion and increased calcium reabsorption in the proximal tubule. Therefore, the medication is frequently used for preventing development of most calcium-based stones.
3. Which are the following strategies would NOT prevent nephrolithiasis recurrence in a patient with uric acid stones?
Potassium citrate supplementation
Targeting a urine pH less than 5.5
Correct! All these strategies, including potassium citrate supplementation, low-sodium diet, and allopurinol use have potential roles in preventing uric acid stone recurrence. However, reducing the urine pH to less than 5.5 will actually promote uric acid precipitation. With uric acid stones, alkalinization of urine prevents crystallization.
4. Obesity is a known risk factor for nephrolithiasis. Therefore, weight loss/bariatric surgery reduces the risk of calcium oxalate stone formation.
Correct! While obesity is a known risk factor for nephrolithiasis, bariatric surgery also could increase the risk of calcium oxalate stone formation. This is related to enteric hyperoxaluria. Increased free fatty acids in the intestinal lumen bind to calcium after such surgery, thereby increasing the amount of oxalate available for intestinal absorption. This will increase risk of calcium oxalate stone formation.
5. JW has a medical history of long-standing Sjogren syndrome. She’s currently experiencing her second episode of nephrolithiasis. Your metabolic evaluation revealed the possibility of calcium phosphate stones. Which of the following interventions would NOT reduce the risk of future stone recurrence?
Increase fluid intake to 2L per day
Start high calcium diet
Start potassium citrate and aim for urine pH above 7
Correct! Distal renal tubular acidosis (dRTA) can often be seen in autoimmune conditions like Sjogren’s syndrome. As we know, a high urine pH is typical in dRTA. This will also increase risk of calcium phosphate stone formation. Increasing the urine pH above 7 would further increase risk of calcium phosphate stone formation, and most recommendations advise not to let the pH rise above 6.5-7.
Start thiazide diuretic
6. Percutaneous nephrolithotomy monotherapy is the treatment of choice for staghorn calculi.
Correct! The American Urological Association guideline (http://bit.ly/2dGQ3Ic
) recommends percutaneous nephrolithotomy as the treatment of choice for staghorn calculi.
Post prepared by Dr. Veeraish Chauhan, AJKD Blog Contributor. For a PDF version of the questions & answers, please click here.
[Note: The original version of this post included a variation of the last true/false statement. It previously read, “percutaneous nephrolithotomy monotherapy is the treatment of choice for infected staghorn calculi.” It has since been changed to omit the word “infected.”]