A kidney stone is a hard deposit of minerals and salts that forms inside the kidney. These stones vary widely in size, ranging from tiny specks to masses that can fill the kidney’s collecting system. A 5-millimeter stone is frequently detected, placing it at a size threshold where spontaneous passage is often questioned. This size is considered moderate, and understanding the likelihood of natural passage, expected symptoms, and necessary home management is important for navigating this condition.
Probability of Passage Based on Stone Size
The size of the stone is the primary factor predicting its journey through the urinary tract. Stones smaller than 5 millimeters have a high probability of passing spontaneously, often exceeding 70%. A 5-millimeter stone sits on the border of this range, with spontaneous passage rates typically falling between 50% and 65% within a reasonable observation period.
The influence of size relates to the anatomy of the ureter, the tube connecting the kidney to the bladder. The ureter’s inner diameter is typically narrow, measuring about 3 to 4 millimeters. Although the ureter can stretch, a 5-millimeter stone is large enough to create a significant obstruction. The stone’s location also plays a role; stones that have reached the lower (distal) part of the ureter have a much higher chance of passage than those lodged higher up near the kidney.
Symptoms and Timeline of Stone Passage
When a stone dislodges from the kidney and enters the ureter, it initiates renal colic. This is characterized by sudden, severe pain, typically felt in the flank or back, which radiates toward the abdomen and groin as the stone moves lower. The intense pain results from the ureter attempting to push the stone along through muscle contractions, combined with pressure buildup as urine backs up into the kidney.
The timeline for a 5-millimeter stone to pass is highly variable, often taking several weeks. Stones in the 4- to 6-millimeter range can take approximately 39 to 45 days to pass, compared to smaller stones which pass faster. Pain tends to fluctuate significantly during this period, often coming in waves as the ureter spasms around the stone. Blood in the urine (hematuria) is a common symptom resulting from the stone scraping the ureteral lining.
Managing Pain and Hydration at Home
Managing the pain associated with passing a stone is important, and nonsteroidal anti-inflammatory drugs (NSAIDs) are an effective first-line treatment. NSAIDs like ibuprofen reduce both pain and inflammation-induced swelling in the ureter, which can help relax the smooth muscle and facilitate stone passage. This dual action is often considered superior to acetaminophen, which only targets pain.
Maintaining a high fluid intake assists the stone’s movement. Patients should drink enough water to produce 2 to 3 liters of clear or pale yellow urine daily. This high urine volume creates hydrostatic pressure behind the stone, encouraging it to move forward. Collecting the stone once it passes is important for analysis, which is accomplished by urinating through a fine-mesh strainer until the pain-free period has lasted for at least 24 hours.
Critical Warning Signs Requiring Immediate Medical Attention
While many 5-millimeter stones pass on their own, certain symptoms indicate a complication requiring immediate medical intervention. The most serious sign is the development of a fever, especially when accompanied by chills, which suggests a urinary tract infection has developed behind the obstruction. A stone combined with infection constitutes a urologic emergency that can rapidly lead to sepsis.
Other signs for concern include intractable pain that is no longer controlled by prescribed medication, or persistent nausea and vomiting that prevents the patient from staying hydrated orally. Furthermore, a complete inability to urinate, or a significant decrease in urine output, signals a total obstruction that may damage the kidney. These symptoms indicate that watchful waiting is no longer safe and that a urologist must intervene.