From the Guidelines
Urinary stones smaller than 5 millimeters in diameter can typically pass independently without medical intervention, with a spontaneous passage rate of 68% 1. Stones between 5-10 millimeters have a moderate chance of passing on their own, with a spontaneous passage rate of 47% 1, though they may require more time and cause more discomfort. The location of the stone in the urinary tract also affects passage rates, with stones in the lower ureter having better chances of spontaneous passage than those in the upper ureter or kidney. Some key points to consider when managing urinary stones include:
- Maintaining adequate hydration by drinking 2-3 liters of water daily
- Taking prescribed pain medications as needed
- Considering alpha-blockers like tamsulosin (0.4 mg daily) which can relax the ureter and improve passage rates, especially for stones 5-10 mm in size 1
- The ability of stones to pass naturally depends on their size, shape, location, and individual patient factors such as anatomy and prior stone history. It is also important to note that patients with uncomplicated ureteral stones ≤10 mm should be offered observation, and those with distal stones of similar size should be offered medical expulsive therapy (MET) with alpha-blockers 1.
From the Research
Urinary Stone Size and Spontaneous Passage
- The size of urinary stones that can pass independently is a crucial factor in determining the treatment approach 2, 3, 4, 5.
- Studies have shown that stones with a diameter of less than 5 mm are more likely to pass spontaneously through the ureter 2, 3, 5.
- For ureteral stones, the spontaneous passage rate is high for stones with a width of 0-2 mm (98%), 3 mm (98%), and 4 mm (81%), but decreases significantly for stones with a width of 5 mm (65%) and 6 mm (33%) 2.
- A mechanical analysis of kidney stone passage through the ureter suggests that the critical size of kidney stone is related to ureter size, and is approximately 11%-22% larger than the inner diameter of the ureter 3.
- The efficacy of alpha-blockers for kidney stones in adults also depends on stone size, with benefits seen for stones 5-10 mm without lithotripsy, and for stones >10 mm with lithotripsy 4.
Stone Size and Passage Time
- The time to stone passage varies depending on stone size, with smaller stones passing more quickly 5.
- For stones 2 mm or smaller, the average time to passage is 8.2 days, while for stones 2-4 mm, the average time to passage is 12.2 days, and for stones 4 mm or greater, the average time to passage is 22.1 days 5.
- Multivariate analysis has shown that stone size, location, and side are statistically related to stone passage interval, with smaller, more distal, and right-sided stones more likely to pass spontaneously 5.