Kidney stones are mineral and salt crystals that form within the kidney. While they remain in the kidney, they typically cause no symptoms. Severe pain, known as renal colic, begins when the stone detaches and enters the narrow tubes of the urinary tract. The duration of this passage is highly unpredictable and depends on several factors specific to the stone and the individual’s anatomy.
The Typical Timeline and Journey
The process of passing a kidney stone begins when it leaves the kidney and enters the ureter, the narrow tube connecting the kidney to the bladder. Most stones that are small enough to pass naturally will do so within a period ranging from a few weeks to over a month.
The size of the stone is the most significant determinant of how fast it will pass. Approximately 80% of stones measuring less than 4 millimeters (mm) will pass on their own, often within an average of 31 days. For medium-sized stones, those between 4 mm and 6 mm, the natural passage rate decreases to about 60%, and the time required extends to an average of 45 days. Stones larger than 6 mm have a significantly reduced chance of passing spontaneously, with only about 20% clearing the ureter without medical intervention.
Once the stone successfully navigates the ureter and reaches the bladder, the period of severe, intermittent pain typically ends. The final stage involves the stone passing from the bladder and out through the urethra. This final expulsion is usually quick, often occurring within a few hours to a few days after the stone enters the bladder.
Key Factors Influencing Passage Rate
Beyond size, the stone’s exact location within the urinary tract plays a significant role in determining its speed of passage. The ureter has three naturally narrow points where a stone is most likely to become lodged, which can halt movement entirely. Stones located in the upper ureter, closer to the kidney, have a longer distance to travel and are associated with a lower spontaneous passage rate.
Stones that have already moved into the distal ureter, meaning the segment closest to the bladder, are significantly more likely to pass on their own. The threshold of 5 mm is generally used to predict the likelihood of successful natural passage, as stones exceeding this width face mechanical difficulty navigating the ureteral lumen.
Strategies to Encourage Stone Movement
While the stone’s inherent properties influence passage, several strategies can be employed to promote faster movement. Increasing fluid intake is essential, as high water consumption increases urine volume and flow. This increased pressure behind the stone can help push it along the ureter and reduce the concentration of stone-forming minerals.
A healthcare provider may prescribe alpha-blockers, such as tamsulosin, to facilitate passage. These drugs work by relaxing the smooth muscles of the ureter walls, widening the ureter. This makes it easier for stones, particularly those between 5 mm and 10 mm, to move through the narrow tube.
Engaging in mild physical activity can also assist the process by helping the stone respond to gravity and the natural muscular contractions of the ureter, known as peristalsis. Simple activities like walking or light jogging can provide the gentle movement needed to encourage the stone to shift.
When Immediate Medical Intervention is Necessary
When a stone is taking too long to pass or causes complications, medical intervention becomes necessary. Persistent, intractable pain that cannot be managed with prescription medication is a primary indicator for a procedural approach. The presence of a fever and chills alongside the pain suggests a urinary tract infection has developed behind the obstruction, constituting a medical emergency.
A stone that completely blocks the flow of urine can cause the kidney to swell, a condition called hydronephrosis, leading to potential damage. If a stone has not shown any movement or has not passed after an observation period of approximately four to six weeks, a urologist will typically recommend a procedure. Common treatments include extracorporeal shock wave lithotripsy (ESWL), which uses targeted sound waves to break the stone into smaller, passable fragments. Alternatively, a ureteroscopy involves inserting a thin scope to directly remove the stone or break it apart with a laser.