Monday, November 4, 2013

Just drinking water may not prevent another kidney stone

- Jennifer Middleton, MD, MPH

"I know what it is, doc - I've had stones lots of times before."
A patient of my colleague's said this to me a few weeks ago in the office, and, sure enough, the patient was correct.  2 days of colicky left flank pain and dysuria had, indeed, turned out to be recurrent nephrolithiasis.

My training regarding the counseling of these patients to prevent recurrence basically consisted of "drink water.  2 liters a day."  This patient had been doing that, yet still ended up with a stone again.  I vaguely recalled that there were some other things patients could try to reduce nephrolithiasis recurrences, but I couldn't remember anything specific.  I realized, then, that I had abdicated that decision making to the specialists who usually follow these patients.

One of this week's American Family Physician's POEMs discussed Fink et al's systematic review on this very topic.  The researchers examined 28 studies regarding prevention of recurrent nephrolithiasis using appropriate systematic review methodology and found that water works fine for preventing the second episode after an initial event.  But after the second episode, water by itself didn't do as well.  Participants with multiple stone episodes who added a thiazide diuretic, a citrate (for example, potassium citrate), or allopurinol to their 2 liters of water a day, though, had fewer recurrences.

This systematic review did a nice job of discussing how to tailor prevention based on the patient. Patients with calcium stones benefited from citrates and thiazides, regardless of their baseline calcium level. Allopurinol, of course, worked for patients with high serum uric acid levels or low urinary uric acid excretion.  Unfortunately, for struvite stones, findings were less promising; the reviewers looked at 3 studies that touted acetohydroxamic acid (AHA) as a preventive, but they felt that the strength of evidence from these only fair-quality trials was too low to recommend AHA at this time.  The reviewers also found that serum or urinary calcium levels didn't help to predict if a patient was more or less likely to have a recurrence, though serum uric acid levels can.

As a family doc, I want to be aware of what my specialist colleagues do, so I can appropriately reinforce their counseling and recommendations with our mutual patients.  I appreciated AFP's discussion of this systematic review and am very glad to have expanded my nephrolithiasis prevention toolkit.

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