Experts discuss prevalence, incidence, and predictors of kidney stones

In this video, Ben H. Chew, MD, MSc, FRCSC, and Naeem Bhojani, MD, FRCSC, discuss the background and key findings from the study, “Prevalence, Incidence, and Determinants of Kidney Stones in a Nationally Representative Sample of US Adults.” Chew is a urologist at the University of British Columbia and Bhojani is an associate professor of urology at the University of Montreal.

Video Transcript:

Bhojani: This is a study that we did using the NHANES dataset. This is a dataset that is based on interviews, laboratory tests, and physical examinations. It's been used in the past. We examined it over a 3-year period from 2017 to 2020. The 2 main things we wanted to look at was incidence and prevalence of kidney stones.

Chew: NHANES stands for National Health and Nutrition Examination Survey. They follow people longitudinally, looking at things like supplements and cancer and various things, longitudinally. It's self-reported, and they follow a cohort, which is supposed to be representative of 240 million Americans over this time. This analysis looked at just over 9200 participants with incidence and prevalence data averaged around 51 years of age and about half male and half female. The mean body mass index was pretty indicative of the American public, it was about 30 plus or minus 8. Naeem, what do you think was the big finding from here? We haven't had prevalence data for a long time, where we've looked at people. This was a new look at how common is kidney stone disease? Tell us what we found.

Bhojani: Just like you said, the nice thing about this study is that it's contemporary. We're looking at data that is more recent, not historical data. We found a few very interesting findings. First, we found that the prevalence of kidney stones in the US population is about 10%. But what's more interesting for us is that the prevalence in women was almost the same as in men.

Chew: That's very interesting, because before it used to be a disease more of men than women. It used to be about 3 to 1, men to women.

Bhojani: We've always said that women are catching up to men, that their incidence prevalence is catching up. But this is actual data showing that they have caught up to us, unfortunately.

Chew: Yes, unfortunately. This is not something you want equality with, for sure. Now, why do we think this is? What are some of our hypotheses?

Bhojani: I think it's really important to understand that with this dataset, we're providing data on incidence and prevalence. But the cause of something, we can't find that in this dataset. What we're getting now is our hypothesis. We think that the increase in prevalence in women is probably due to metabolic factors– obesity, diabetes, insulin resistance–all the things that that we see that are associated with kidney stones.

Chew: In fact, on multivariate analysis, they wanted to look at other health concerns that raise people's risk of getting kidney stones and the 3 things that came up from the study where the history of gallstones, hypertension, and chronic kidney disease. They were all important predictors of outcomes of both having stone. Gall stones, hypertension, chronic kidney disease, we know these are all things with the metabolic syndrome, which is unfortunately increasing in in today's modern world. So, that's probably why women are catching up. So, Naeem, we know the prevalence, which is basically how much it exists in this population, is around the same as what it was historically, around 9.9%. The incidence–there's a bit of a limitation there, because we had to ask people, "did you pass a kidney stone in the last year"–and that incidence was about 1.8% of people. Maybe you could just touch on some of the problems that we may not be capturing with that 1.8% of people who pass a stone each year.

Bhojani: So, just like you said, there's about just under 2% of patients who will pass a stone every year, which might seem low. But that's a lot of passing of stones, for the amount of patients who have stones. And again, like you mentioned, we're underestimating this number, because we were asking about stones that are passed, not the ones that were operated on or [patients that] had to be hospitalized and then have surgery. So, I think it's probably a little bit higher than that that number, but it's a significant number. I think it's important to consider that these patients, if they undergo surgery or if they have the pass a stone, it can be quite a traumatic event. So, it's important to keep that number in mind. The factors that predict incidence were the same as for prevalence, as we mentioned. So chronic kidney disease, gall stones, and hypertension.

This transcription has been edited for clarity.