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Nephrology/Uric Acid Stone

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Question
Hi, I was diagnosed with a 5mm uric acid stone recently.  Was told to drink a lot of water and reduce sodium intake.  I have a couple of questions I didn't think of at the time.  

What happens if it gets bigger and how big would be too big?

Also hypothetically say that it just stays about the same size, is that something that would produce a chronic kidney issue or would that be ok if it's aysmptomatic?

I have no pain and occasional urine tests with just small traces of blood.

Thanks.

Answer
Hello, Eric.  Good to hear from you.

Uric acid kidney stones are not Uncommon.  They constitute approximate 10% of all kidney stones formed.

In general, stones that are LESS THAN 5mm in diameter tend to pass spontaneously.  Stones that are greater than 7mm in diameter usually require some sort of urologic intervention.  Yours is right on the line and I agree with the apparent decision, not to intervene surgically. Watchful waiting is in order. If the stone increases in size, to the 7mm cut off point, it will need to be extracted be a urologist.

The stone, per se, is not going to effect your kidney function and barring complications, such as infection, it will not effect your kidney function or your health.

It is important to ask why it is that you have a uric acid stone.  Do you have gout?  Is the uric acid level of your blood elevated (hyperuricemia)? You need to have your kidney function assessed with a serum creatinine and you serum uric acid levels checked.

If you are hyperuricemic, you should be receiving a medication to reduce your uric acid, such as probebecid (if your kidney function is normal) or allopurinol.  Additionally, a stone specialist would almost certainly recommend that you be placed on a low protein diet (1-1.5 grams of protein per day) and that your urine be alkalinized.  A low protein diet would help with that but there exists a medication called diamox that would help you produce an alkaline urine, as well.  I think you would benefit from that medication.

A low salt diet is prescribed to reduce calcium excretion into your urine.  Some stones are mixed with uric acid and calcium and if that situation is the case with you, a low salt diet would be beneficial to you. Therefore, I would not be opposed to dietary salt restriction.  Americans eat much to much salt, anyway!

Lastly,  Small quantities of blood in the urine (microhematuria), although seen in cases of kidney stone, is, also, the hallmark of kidney cancer. Additionally, having a stone doe not protect one from developing kidney cancer.  I don't know your age, but if you are over 40 years old, I would recommend that you be screened annually for renal cell cancer with either ultrasound or a helical C T scan.  The former exposes you to less radiation but is, also,  less accurate than the CT.

Eric, I hope that this helps you.,

Feel free to follow up, if you wish.  Good luck to you.

Sincerely,

Dr Falkinburg  

Nephrology

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Newell R. Falkinburg, M.D., FACP

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I am a board certified nephrologist and emeritus professor of medicine at a major medical school and past Director of Nephrology & Hypertension at a university affiliated hospital. I have expertise in all areas of clinical nephrology, dialysis, transplantation and plasmapheresis.

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Professor of medicine Director of Nephrology

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