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This blog aims to make "evidence-based medicine" understandable to the lay person
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Thursday, May 16, 2013

Diagnosis, treatment, and diet for people with kidney stones

Since we have been discussing kidney stones over the last few weeks, I wanted to highlight a few points about the diagnosis and treatment of kidney stones, as it pertains to patients. I am not going to get in to the technical details of what a nephrologist or a urologist would do. My idea is to emphasize what you can do to complement your physician's treatment plan.

One of the perks of practicing nephrology in Bradenton, Florida, is that you get a pretty good experience seeing patients with kidney stones. Maybe it is the weather! Most patients that I see have already received a diagnosis of kidney stones (nephrolithiasis or urolithiasis) via imaging studies by the time I see them in my clinic. Imaging studies used to diagnose kidney stones include CT scans, X-rays, or ultrasounds. The latter two modalities can often miss certain types of stones (like uric acid), which is why CT scans are considered the "gold standard".

The usual narrative from the patient runs something like..."Doc, I had excruciating flank (or groin) pain. I went to the ER, and had a CT scan which showed a stone. The stone passed/was removed. I got my pain meds and returned home". The End. Certain things rile me about this all-too-familiar story. What we usually end up treating are the disease symptoms, and not the disease itself. In fact, I tend to look at kidney stones as an a downstream effect of an abnormal metabolic state (which happens to be the real disease; for instance, hyperoxaluria, where you pee out too much oxalate in the urine). Now, it wouldn't make much sense if you don't treat the hyperoxaluria after you get the stone out, would it?! Unfortunately, that is what usually happens. Patients are seldom set up to have a complete metabolic evaluation to determine the risk factors for them forming stones in the first place. Most of the times, our ERs do not do a good job of sending the stone for chemical analysis. This is inexcusable in my opinion. These two tests provide invaluable information that would determine treatment course. This is one of those few medical entities where "how" you diagnose a disease is as important as "what" you diagnose.

So what is this metabolic evaluation? This test often involves a few blood tests (for instance, checking your calcium, uric acid, PTH levels, etc), and perhaps more importantly, a 24-hour collection of your urine to see if you peeing out too much calcium, oxalate, phosphate, etc. (factors that increase risk of stone formation). Conversely, you could be peeing out too little citrate, or your urine could be to be too acidic or alkaline, or you could have a very concentrated urine; all of which would also increase your stone risk. In my practice, I prefer doing at least two of these collections initially. Similarly, using the stone as a resource of knowledge, rather than just a novelty to be kept on your shelf will go a long way as well. Do not throw the stone away! Have a physician send it for analysis. Knowing the specific risk factors will help your physician prescribe treatments like the amount of water intake, or medications like chlorthalidone, HCTZ, potassium citrate, etc. These will greatly reduce the risk of your forming another stone. As you can see, in this case, prevention goes hand in hand with cure.


Spinach is high in oxalate and should be avoided if you have high urine oxalate
(Image courtesy of smarnad/ FreeDigitalPhotos.net)


What is your role in all of this? As far as diagnosis goes, insist on having the stone sent in for analysis. If you are not sure, or if you pass the stone at home, hold on to it and bring it to your favorite nephrologist or urologist. Once the physician prescribes the appropriate treatment, ask for a diet plan. This has a huge influence of future stone risk, and you are really in the driver's seat as far as this aspect of treatment goes.  Ask for a referral to a dietitian  who specializes in kidney stone prevention. Here are a few other pointers that you should remember:

1) Think water, water, and water. Assuming you do not have any major contraindications to increased water intake (like congestive heart failure, cirrhosis, low sodium in your blood, etc), the traditional recommendation is to drink at least 64 ozs or about 2 liters of water daily. However, we all know that even with this intake, the amount of urine you make will also depend on external factors like the weather, or whether you spent the day playing tennis! Hence, a better recommendation is to aim to drink enough water so as to produce 64 ozs or about 2 liters of (ideally, clear) urine daily. In other words, if it is hot out and you see that your urine looks dark amber/concentrated, drink more. Some specific kinds of kidney stones would require the intake of even higher amounts (up to 4 liters) of water daily.

2) When I say water, I mean water. I do not mean colas, gatorade, fruit punch, etc. A lot of these drinks would have sugar or sodium or phosphoric acid in them, all of which would increase your stone risk. Therefore, and to spare my patients any confusion with fluid intake, I ask them to stick to good old H2O.

3) Stick to a low sodium diet; since sodium will increase the amount of calcium you pee out. Cut out the sugar (sucrose, fructose) as well.

4) A diet high in dietary calcium is advised (so milk is good, but no calcium supplements). I have discussed this conundrum in my previous post.

5) There is conflicting evidence on whether tea increases your risk. Most tea varieties are high in oxalate, a major risk for stone formation, but to what extent is this oxalate actually absorbed and excreted in to the urine is still controversial. Green tea is purportedly better than black tea on account of its lower oxalate content. Other foods that you need to watch for oxalate include spinach, cereal, potatoes, bread, rhubarb, chocolate, nuts, and beets. A more comprehensive list is available here.

6) Supplemental vitamin C is an oxalate precursor and is not recommended.

7) Increase your potassium and phytate (grains, legumes) intake.

8) Going vegetarian might help. Studies have shown that animal protein intake is associated with a higher stone risk.

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