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How are kidney stones diagnosed?


I have spent the last two weeks discussing the very common “kidney stone”. I have explained why an ultrasound by itself is insufficient to diagnose a kidney stone, because it can miss potentially serious–life threatening conditions, especially when the doctor does not examine the patient, but depends on the ultrasound to make the diagnosis for him. This happens because the doctor is either too busy or assumes the pain is obviously kidney pain. So, how do you know that you have a stone in the kidney?{{more}}

The answer is you usually do not know, because most kidney stones are asymptomatic. They do not cause problems. They remain in the kidney for years and may never cause any problems. Rarely, you might have some pain. The pain is usually dull and in the small of the back. This pain may be caused when the stone is moving and is trying to pass, or because the stone has created infection in the kidney. Big stones (half inch or more) do not move from the kidney, they remain in the kidney and may cause an intermittent dull ache once every few months or years. The very small stones (less than one fifth of an inch or 5mm) tend to pass and you may not even know. The medium size stones (from 5-10 mm) tend to pass with some amount of pain, discomfort, nausea, vomiting and blood in the urine, because when they are passing they create blockage on the kidney and bruise the lining of the ureter.

The diagnosis of a kidney stone is usually made incidentally. It’s detected “by the way”, using an ultrasound. The ultrasound examination is usually done for abdominal pain, but the “kidney stone” is “seen” and is usually blamed for the pain. It is not usually the cause of the pain, but since it may be the only thing “seen” on the ultrasound, it is usually blamed for the pain. I have discussed the danger with this already. Kidney stones seen on ultrasound should be confirmed with either a plain X-ray of the abdomen, or if the ultrasound suggests that there is a significant amount of blockage being caused by a kidney stone, then an intravenous urogram (IVU) is done. This is an X-ray dye test of the kidney and should not be done without discussing the risks of the tests with the patient. These risks include possible allergic reaction to the dye and excessive exposure to radiation because 5 -10 X-ray pictures are taken.

If the patient cannot tolerate or does not want the dye and really wants to know if he/she has a stone, then a plain (non-contrast) CT scan of the abdomen can be done. This is almost 100 per cent accurate in detecting a stone. It will also identify the possible other causes for abdominal pain, especially if it is combined with contrast (dye) given orally and intravenously. The CT scan is now the gold standard for detecting stones. Unfortunately, the CT scan is expensive, compared to an IVU or ultrasound. Additionally, in our environment, the test is not routine and has to be “scheduled” usually weeks before, unless it is emergent, which it usually isn’t.

So, in summary, you usually don’t know you have a stone and when you do, it’s usually because the stone seen on the ultrasound or the X-ray is an innocent bystander. The pain is usually caused by another pathology. The CT scan is the best, but most expensive way of diagnosing a stone; however, in the absence of such an ultrasound combined with a plain X-ray of the abdomen and a urinalysis or an IVU will suffice. Next week, we will look at what causes stones and how they are treated or prevented.

For comments or question contact:

Dr Rohan Deshong

Tel: (784) 456-2785