Podcast 1029: Kidney Stone Size

Contributor: Travis Barlock, MD

Educational Pearls:

Kidney stones: hard deposits that form inside the kidneys when urine becomes too concentrated

• The most common type is calcium oxalate

• Stones can travel from the kidney to the ureter → causes obstruction and renal colic

Stone size predicts likelihood of spontaneous passage → the smaller the stone, the more likely it is to spontaneously pass

• These are approximate estimates, not absolute cutoffs. Published studies use different size categories and follow-up periods.

• ≤5 mm: 68–90%+

• 5–7 mm: ~50–70%

• >7 mm: ~30% but varies by location (more likely to require intervention)

Stone size does not correlate with pain severity

• Pain is driven largely by increased pressure, ureteral spasm, and inflammation

• Pain can vary with anatomy and obstruction

• A very small stone can cause excruciating pain and a larger stone can cause relatively minimal discomfort

The most important thing: rule out infection!

• Always evaluate for a urinary tract infection in a patient presenting with a suspected obstructing stone

• Obtain urinalysis and look for leukocyte esterase, nitrites, pyuria, and bacteriuria as well as clinical signs of infection such as fever, chills, or tachycardia

References

1. Coll DM, Varanelli MJ, Smith RC. Relationship of spontaneous passage of ureteral calculi to stone size and location as revealed by unenhanced helical CT. AJR Am J Roentgenol. 2002 Jan;178(1):101-3. doi: 10.2214/ajr.178.1.1780101. PMID: 11756098.

2. Gourlay K, Splinter G, Hayward J, Innes G. Does pain severity predict stone characteristics or outcomes in emergency department patients with acute renal colic? Am J Emerg Med. 2021 Jul;45:37-41. doi: 10.1016/j.ajem.2021.02.049. Epub 2021 Feb 23. PMID: 33647760.

Summarized by Meg Joyce, MS3 | Edited by Meg Joyce & Ahmed Abdel-Hafiz, NREMT-P

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