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Kidney Stones

Are kidney stones really worse in summer?

Korean data answer this more precisely than a season. The delay between a hot day and the hospital is under five days.

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Answer

Yes. In a time-series analysis of 687,833 urolithiasis patients across six Korean cities from 2009 to 2013, presentations rose with daily mean temperature and fell with humidity in every city, with the effect appearing within five days — and national emergency data show an August peak of 35,927 visits against 24,008 in February.

Key takeaways

  • A time-series study of 687,833 urolithiasis patients in Seoul, Incheon, Daejeon, Gwangju, Daegu and Busan from 2009 to 2013 found presentations rising with mean daily temperature in all six cities.
  • Relative humidity ran the other way: higher humidity was associated with fewer presentations, again in all six cities.
  • The lag effect was within five days, so a hot spell shows up in hospitals inside the same week.
  • Korea's national emergency department data recorded 35,927 urolithiasis visits in August against 24,008 in February.
  • Emergency visits clustered at weekends and around 6 a.m. and 8 p.m.
  • Calcium oxalate stones, the largest group in Korean stone analyses, were most frequent in summer and least frequent in spring.

That stones are a summer problem is one of the oldest observations in urology. Korean data turn it from an impression into a measurement, and the measurement is more specific than a season.

What was measured

A study in the Journal of Korean Medical Science analysed 687,833 urolithiasis patients from 2009 to 2013 across six large cities — Seoul, Incheon, Daejeon, Gwangju, Daegu and Busan — relating daily presentations to daily weather rather than comparing one month with another.

Presentations rose with mean daily temperature in every one of the six cities, and fell as relative humidity rose, again in every city. The cities behaved alike: the test for heterogeneity in the temperature effect gave a P value of 0.136, with about a third of the variability attributable to differences between them.

under 5 days

the delay between a rise in daily mean temperature and the rise in urolithiasis presentations, across six Korean citiesChi BH et al., Journal of Korean Medical Science, 2017

The same shape in the national figures

Korea's National Emergency Department Information System shows the annual pattern independently. Across 2014 to 2016, urolithiasis visits peaked at 35,927 in August against 24,008 in February, and clustered at weekends and around 6 a.m. and 8 p.m. — the distribution of a stone passing overnight or on a day off rather than during a working appointment.

Stone composition follows the season too. In 33,078 Korean stone analyses, calcium oxalate — the largest group — was most frequent in summer and least frequent in spring.

What this does and does not prove

The six-city study relates city-level daily counts to city-level daily weather. It holds no information about any individual: not how much water anyone drank, not who worked outdoors, not who had formed a stone before. The usual explanation — that heat concentrates the urine through fluid loss — fits the data completely and is not demonstrated by them.

Sources

  1. 1

    Chi BH, Chang IH, Choi SY, Suh DC, Chang CW, Choi YJ, Lee SY

    Daily mean temperature and urolithiasis presentation in six cities in Korea: time-series analysis

    Journal of Korean Medical Science 2017;32(6):999-1008

    doi:10.3346/jkms.2017.32.6.999 · PMID:28480659

    https://doi.org/10.3346/jkms.2017.32.6.999
  2. 2

    Kim JW, Kim JY, Ahn ST, Oh MM, Moon DG, Park HS

    Analysis of patients with urolithiasis visiting the emergency department between 2014 and 2016 in Korea: data from the National Emergency Department Information System

    Scientific Reports 2019;9(1):16630

    doi:10.1038/s41598-019-52950-8 · PMID:31719555

    https://doi.org/10.1038/s41598-019-52950-8
  3. 3

    Jung HD, Seo IY, Lee JY

    Large database study of urinary stone composition in South Korea: Korean Society of Endourology and Robotics (KSER) research series

    Investigative and Clinical Urology 2021;62(4):462-469

    doi:10.4111/icu.20210039 · PMID:34190438

    https://doi.org/10.4111/icu.20210039