What is the likelihood and expected timeframe for spontaneous passage of a 4.5 millimeter (mm) renal calculus (kidney stone)?

From the Guidelines

A 4.5 mm renal stone has approximately a 47% chance of passing spontaneously without surgical intervention, as suggested by the meta-analysis of three groups (104 patients) in the 2007 guideline for the management of ureteral calculi 1. The average time to pass a stone of this size can vary significantly between individuals, but it is generally recommended to wait for 4-6 weeks before considering intervention, as stated in the 2016 American Urological Association/Endourological Society guideline, part II 1. Some key points to consider during this time include:

• Pain management with medications such as ibuprofen (600-800 mg every 6-8 hours) or naproxen (500 mg twice daily) to help manage discomfort
• Alpha-blocker medications like tamsulosin (0.4 mg daily) may increase the likelihood and speed of stone passage by relaxing the ureter muscles, as shown in the meta-analysis of six studies examining alpha blockers (280 patients) in the 2007 guideline 1
• Drinking plenty of fluids (2-3 liters daily) to help flush the stone through the urinary system
• Straining urine using a fine mesh strainer to catch the stone for analysis
• Seeking immediate medical attention if severe pain uncontrolled by medication, fever, chills, nausea, vomiting, or inability to urinate occur, as these may indicate complications like infection or complete urinary blockage If the stone hasn't passed within 4-6 weeks, the doctor may recommend intervention such as shock wave lithotripsy or ureteroscopy to remove the stone, with URS being the recommended first-line therapy for patients with mid or distal ureteral stones who require intervention, as stated in the 2016 guideline 1.

From the Research

Likelihood of Spontaneous Passage

• The likelihood of spontaneous passage of a 4.5 mm renal calculus is not directly addressed in the provided studies, but the use of alpha-blockers, such as tamsulosin, as a medical expulsive therapy (MET) has been shown to improve stone expulsion rates 2, 3, 4, 5.
• A study on tamsulosin as an expulsive therapy for steinstrasse after extracorporeal shock wave lithotripsy found that stone expulsion occurred in 72.7% of patients receiving tamsulosin, compared to 56.8% in the control group 3.
• Another study found that the use of tamsulosin as MET following shock wave lithotripsy facilitates expulsion of retained residual fragments, with a stone-free rate of 73.8% in the tamsulosin group, compared to 59.6% in the placebo group 4.

Expected Timeframe for Spontaneous Passage

• The expected timeframe for spontaneous passage of a 4.5 mm renal calculus is not directly addressed in the provided studies, but the use of alpha-blockers has been shown to reduce stone clearance time 5.
• A study found that the median time for stone-free status was 30 days in the tamsulosin arm, compared to 36 days in the placebo arm 4.
• Another study found that alpha-blockers may reduce stone clearance time in days, with a mean difference of -3.74 days 5.

Factors Influencing Spontaneous Passage

• The size and location of the stone, as well as the use of alpha-blockers, can influence the likelihood and timeframe of spontaneous passage 2, 3, 4, 5.
• A study found that the stone-free rate was higher in patients with smaller stones, and that the use of tamsulosin did not increase the stone-free rate in patients with larger stones 6.