Ask Do I really need that repeat x-ray?

March 17, 2012

In mid-November I began to have episodes of blood in my urine. I went to a urologist who did a CT (with and without contrast), a cystoscopy, and a urine cytology as well as cultures. All the results were negative for growth, etc. However, the CT scan determined I had 4 kidney stones. The largest is 5mm and is located in the left lower renal pole with two other smaller stones in the left kidney and one tiny stone in the right kidney. There is no obstruction or hydronephrosis. 

The urologist wanted me to come back in three months, for a KUB. I did not agree with that as I felt it was too much radiation in a short amount of time and requested an ultrasound which the urologist refuses to perform. 

My question is, with the size stones should I be able to pass these stones? I am not having any pain or discomfort. I did notice one or maybe two episodes of gross hematuria which the urology staff said was due to the stones possibly moving.

I do not want to cause myself further harm, but I feel that the urologist is itching to blast my stones as she seems to practice big medicine and doesn’t have a wait and see approach. Am I safe to continue to watch the stones and only return if I have great pain, etc?”


Radiation exposure:

Your urologist’s suggestion to get a KUB in 3 months is not unusual. A plain x-ray (KUB) carries a dose of 0.7 mSv as compared to a much higher dose of 15 mSv from a CT scan. For comparison, the annual background radiation most individuals experience is 3.86 mSv just from the environment. Therefore, getting a KUB carries a relatively low dose compared to getting a repeat CT scan. A KUB is also useful in determining whether you are a candidate for ESWL (which uses plain x-ray to aim the shockwaves), as not all stones that are visible on CT are visible on KUB. Ultrasounds are not generally useful for following stones as they are not very accurate at determining the size of stones. This is likely why your urologist does not recommend an ultrasound. An alternative you can consider is waiting longer to get a KUB or repeat CT scan (6, 12, or 24 months).

Stone size:
Stones smaller than 5mm are more likely to be able to pass. As yours are also 5mm or smaller, they can potentially pass successfully (but this does not mean that they won’t hurt while they are passing). Based on one study, 5mm stones have a 50-70% success rate for spontaneous passage. If your stones increase in size over time however, this may no longer be true as the rate of success drops off as stones get larger.

Likelihood that your stones will cause you problems in the near future:
Based on a study of 5,047 adults who underwent CT colonography screening, asymptomatic stones, such as yours, are found in 8% of American adults. In that study, the average stone size was 3mm. Over 10 years, 20.5% of patients with stones, or 1 out of 5, developed a symptomatic “stone episode” requiring intervention. The other 4 out of 5 patients did fine without experiencing a stone episode. This rate of 20% of small stones requiring treatment when observed is consistent with other studies with similar patients. Note though that your stone is slightly larger than 3mm and your corresponding likelihoods may be different.

Hopefully this information can help you to make an informed choice in consultation with your treating urologist.

In our “Ask” section, we field questions from stone formers or their family members. See previous questions and answers here.

About Dr. Mike Nguyen

Mike M Nguyen, MD, MPH, is a urologist and an Associate Professor of Clinical Urology at the Keck School of Medicine of USC in Los Angeles, CA. He specializes in the treatment of kidney stones with both surgery and dietary prevention and the in the treatment of kidney and prostate cancer using the latest robotic surgical approaches. He sees patients at clinics located in Los Angeles, Pasadena, and La Canada, CA. He is the founder of the website.
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One Response to Ask Do I really need that repeat x-ray?

  1. dm says:

    KUB repeat CT scan after 3 months

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