A kidney stone is a hard, crystalline mass formed from concentrated mineral and acid salts in the urine. These masses typically form within the kidney and then travel into the urinary tract. A 3-millimeter (mm) stone is considered small, making it highly likely to pass out of the body without the need for surgical intervention. This spontaneous passage, known as medical expulsive therapy, is the expected course for most small stones.
The Likelihood and Timeline for Passing a 3 mm Stone
The size of a kidney stone is the primary factor determining natural passage. Stones measuring 3 mm are well below the typical 4 mm threshold cited for high passability rates. For stones 4 mm or smaller, the probability of them exiting the body on their own is high, often exceeding 80%.
The small diameter of a 3 mm stone allows it to navigate the ureter, the narrow tube connecting the kidney to the bladder. The timeline for this natural process varies significantly. Stones smaller than 4 mm commonly pass within an average of 31 days once they begin their descent.
While some small stones pass quickly, others can take several weeks depending on their location and shape. Stones closer to the bladder generally have a much higher chance of passing compared to those lodged higher up near the kidney. Treatment for a stone of this size focuses on supporting the body’s natural process while managing associated discomfort.
Managing Discomfort During the Passage Process
The stone’s movement through the narrow ureter typically causes symptoms described as renal colic. The pain is usually felt intensely in the flank or side, just below the ribs, and may radiate downward toward the groin as the stone progresses. This pain often comes in waves, fluctuating in intensity as the ureter spasms to push the stone forward.
Other symptoms include blood in the urine (hematuria), which occurs as the stone irritates the lining of the urinary tract. Patients may also experience a frequent or urgent need to urinate, or a burning sensation during urination, as the stone nears the bladder. Nausea and vomiting are common due to shared nerve connections between the kidneys and the gastrointestinal tract.
Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen are the preferred choice for pain relief, as they help reduce inflammation and pressure within the urinary system. A doctor may advise alternating an NSAID with acetaminophen for better pain control. If nausea and vomiting are prominent, prescription anti-nausea medications, such as ondansetron, can manage these symptoms. Straining all urine until the stone is passed allows the physician to analyze its composition and plan for future prevention.
Actionable Steps to Encourage Stone Movement
Increasing fluid intake significantly is one of the most effective actions to help move a small stone. The aim is to dilute the urine and increase the volume, creating a flushing action to propel the stone along the urinary tract. Doctors often recommend consuming enough fluid to produce a daily urine output of at least 2 to 2.5 liters, typically requiring 3 to 4 liters of total fluid intake per day.
While water is the best choice, beverages like lemon water are helpful because the citrate in lemon binds to calcium, preventing crystal aggregation. Physical activity and movement promote gravity-assisted passage, so remaining mobile rather than sedentary is advised.
A doctor may prescribe specific medications, such as alpha-blockers, to facilitate the stone’s passage. These drugs, commonly used for prostate issues, work by relaxing the smooth muscles in the wall of the ureter. By widening the ureter, alpha-blockers like tamsulosin can increase the stone expulsion rate and reduce the time it takes for the stone to pass.
Recognizing Complications and When to Seek Medical Help
While a 3 mm stone is likely to pass on its own, monitor for signs indicating a blockage or infection. The presence of fever and chills is a serious warning sign that the stone may be causing a urinary tract infection. A fever above 100.4°F (38°C) alongside pain requires immediate medical attention.
Intractable pain, defined as pain that cannot be controlled by prescribed pain medication, is another reason to seek urgent care. Persistent vomiting that prevents keeping down fluids or medications can quickly lead to severe dehydration. A complete inability to urinate suggests the stone has caused a total obstruction of urine flow, which can endanger kidney function. These symptoms indicate the need for prompt evaluation and intervention from a medical professional.