This transcript has been edited for clarity.
Matthew F. Watto, MD: Welcome back to another short Curbsiders video. I'm Dr Matthew Watto, here with my great friend, Dr Paul Nelson Williams.
We're going to talk about kidney stones — a great discussion we had with Dr David Goldfarb. This is a topic that I really did not understand very well. Where should we start?
Paul N. Williams, MD: It's worth noting that kidney stones are hugely prevalent. We're talking like 10% prevalence worldwide. If the patient has had a kidney stone in the past, it's a coin flip that they will have another one, so there's a pretty high recurrence rate. It used to be a preponderance of male patients, something like a 2:1 ratio of men to women, but that has actually leveled out over time. It's about the same now.
In terms of risk factors for who gets urinary stone disease, the list includes patients who are living with diabetes and those with gout or obesity. Anecdotally, which makes sense, kidney stones also occur in patients who don't have adequate access to drinking water or who are frequently dehydrated. So we may see more kidney stones in warmer climates, but also in truck drivers and others who just are not able to hydrate as much as they should.
Watto: People who are worried about access to a bathroom, at work or elsewhere, was another group he talked about.
When we suspect that someone may have a kidney stone, we talked about some of the testing that can be done, such as a low-dose CT scan. I knew we were supposed to get a noncontrast CT scan, but I didn't realize that there are low-dose CTs for this, like we have for lung cancer screening. So if you need to order a CT, you should try to get a low-dose scan. A lot of these patients are young, and they are going to have a ton of CT scans throughout their life.
But Dr Goldfarb did say that you might be able to avoid a scan altogether if the patient says, "I've had kidney stones before; this feels like my last kidney stone." That's probably enough for Dr Goldfarb to avoid doing another CT scan at that time. That was practice-changing for me, for sure. And then another question we asked Dr Goldfarb was whether we should be ordering these lab panels for patients diagnosed with kidney stones.
Williams: For me, if I'm at the point where I'm thinking about ordering some fancy lab panel, I probably should be having that patient see a urinary stone specialist anyway. So it's not a routine part of my workup. The actionable stuff that I'm comfortable looking at would be things like urinalysis. And some of the things he told us about urinalysis were really helpful. Are you ordering the fancy lab panels?
Watto: No, I'm not. I wasn't ordering them before and I won't be ordering them now. I might reach out to the specialist and, say, "Hey, you're seeing this patient. Do you want me to get any testing before they see you?"
You mentioned the urinalysis. Are there any specific pearls you wanted to mention before we talk about prevention of stones? Because that's what these patients always want to know about.
Williams: I want to touch on the urinalysis just to emphasize again that the absence of both gross and microscopic hematuria does not rule out urinary stone disease. The presence of hematuria certainly might heighten your suspicion, but the absence doesn't rule it out. So don't hang your hat on that.
I don't know how often you're looking at the urinary pH. Not as often as I probably should be, but it turns out that this can actually be helpful in terms of stone composition in the right clinical picture. If you have someone with a very low pH (eg, 5-5.5), that might suggest uric acid stones; whereas on the other end, if the pH is 8.5, it might make you think of struvite stones. It made me pause and value the urinalysis even more, which is something that's been a recurring theme on our podcasts.
Watto: I was not looking at urine PH; it wasn't something that I really was comfortable interpreting. But now we've had a couple of recent episodes. We talked about it on the metabolic alkalosis episode as well.
But back to the stone panels. Why do people want to order them? They think if you find out what kind of stone the patient has, you'd be able to better counsel them about how to avoid future stones. But it turns out there's just a lot of basic advice that you can give to patients who are prone to kidney stones. One is to drink 96 oz of water a day, a number that comes from expert opinion. That's what Dr Goldfarb would write in a prescription for his patients back when they used to write prescriptions. But you have to be mindful of the logistics of telling a man with BPH to drink 96 oz of water a day and that he has to be drinking throughout the day, not just all at one time, and to avoid becoming dehydrated. That can be tough.
Some other simple things are taking it easy on the animal protein, which can contribute to uric acid levels; following a low-sodium diet, and trying not to eat too many oxalate-rich foods, which includes a lot of healthy foods. They shouldn't cut them out altogether because these are things like beets, chocolate, berries, nuts, greens, and rhubarb. They should eat oxalate-rich foods in moderation and pair them with dietary calcium — not necessarily from dairy products. Calcium binds oxalate in the gut and excretes it as waste rather than letting it accumulate in the bloodstream and get into the urine, causing stones. That was some of the basic advice that he gave us. Hydrate, take it easy on the animal proteins and the salt, and try to eat your oxalate-rich foods with some calcium. It's all very easy stuff that most patients can do. Paul, have we missed any big highlights?
Williams: Talking about hydration, I want to emphasize this in terms of prevention rather than management. The going theory used to be drink 17 gallons of water a day to help the stone pass. It turns out that increasing your fluid intake doesn't seem to help at all. So you may make the patients more miserable but no more likely to pass the stone. The typical management is NSAIDs for analgesia if the patient can tolerate them, and relaxing as much as possible, but don't have your patients just overhydrating because it is not going to help and may actually make them worse.
Watto: Dr Goldfarb said that the physiology of it is that the kidney is irritated with a stone. Maybe there's a stone stuck in the ureter, so if you hydrate the heck out of the patient, their other kidney is going to be preferentially working. You're just going to put more fluid through that other kidney and the bladder. The patient is going to be peeing a lot, but it's not going to flush the stone out of the irritated kidney.
So, what he said is focus on relaxation — warm baths, meditation. But we didn't get into too many details on other substances. Relaxation may help. For pain control, NSAIDs actually seem to be superior, or at least not inferior to opioids, and certainly have a better risk profile. So NSAIDs are the analgesic of choice unless the patient has a contraindication. There's less need for follow-up analgesia when they're taking NSAIDs as the first-line treatment rather than opioids.
We've talked about how to diagnose kidney stones and how to prevent them. Relaxation is more important than hydration for the patient who is in the middle of an acute stone event. For more great pearls, listen to the full episode: Urinary Stone Disease Will Rock Your World.
Williams: And you can subscribe to The Curbsiders wherever you get your podcasts, or visit thecurbsiders.com to stream the show and check out our show notes and figures. Thanks so much for watching.
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Cite this: Matthew F. Watto, Paul N. Williams. Kidney Stones: What Hurts and What Helps - Medscape - Jan 20, 2022.