Kidney stones are solid formations that develop in the kidneys from minerals and salts found in urine. When these hard deposits move from the kidney into the narrow tubes of the urinary tract, they can cause pain. A common concern for individuals with kidney stones is understanding the likelihood of passing them naturally.
Factors Affecting Passage
While the size of a kidney stone is a primary determinant, several other characteristics also influence whether it can pass through the urinary tract without medical intervention. Stone shape also plays a role; smooth stones pass more easily than those with jagged edges or irregular surfaces, which can irritate the ureter.
The stone’s location within the urinary tract significantly impacts its passage. Stones forming in the kidney might not cause symptoms until they move into the ureter, the tube connecting it to the bladder. Stones closer to the bladder (distal ureter) have a higher probability of natural passage than those higher up or within the kidney. An individual’s unique anatomy, such as the natural width of their ureters, can also affect the ease of stone passage.
Likelihood of Passage by Size
The size of a kidney stone is a significant factor in determining its chance of natural passage. Smaller stones generally have a higher probability of passing without intervention. Stones up to 3 millimeters (mm) in size have a high spontaneous passage rate, around 98%.
As stone size increases, the likelihood of natural passage decreases. Stones around 4 mm have an 80-81% chance of passing on their own, typically within one to two weeks. For stones in the 4-6 mm range, the spontaneous passage rate drops to about 60-65%, and these may take two to three weeks, or even up to 45 days, to pass. Stones larger than 6 mm have a significantly lower chance of passing naturally, with rates around 20-33%. Stones larger than 7 mm rarely pass without medical procedures.
When Stones Require Intervention
When kidney stones are too large to pass naturally, or if they cause severe symptoms, medical intervention becomes necessary. Procedures are often recommended if the stone fails to pass, causes severe pain, leads to infection, or impairs kidney function. Effective treatments are available to manage these larger or problematic stones.
Extracorporeal Shock Wave Lithotripsy (ESWL) is a non-invasive procedure that uses high-energy shock waves directed from outside the body to break the stone into smaller fragments. These smaller pieces can then pass more easily through the urinary tract. ESWL is effective for stones between 4 mm and 2 cm and those located in the kidney or upper ureter.
Ureteroscopy involves inserting a thin, flexible scope through the urethra and bladder, up into the ureter to reach the stone. If the stone is small, it can be removed with a basket-like device. For larger stones, a laser can be passed through the scope to break the stone into smaller pieces, which are then either removed or allowed to pass naturally. This procedure is often used for stones in the ureters or kidneys and is suitable for patients who cannot undergo ESWL.
Percutaneous Nephrolithotomy (PCNL) is a surgical procedure typically reserved for large kidney stones (over 2 cm) or when other treatments have been unsuccessful. A small incision is made in the back to create a direct pathway to the kidney. Through this opening, instruments are used to remove the stone directly or break it into fragments for extraction. PCNL is considered the most effective procedure for large and complex stones.
Coping with a Kidney Stone Episode
Experiencing a kidney stone can be painful, but there are ways to manage the episode and know when to seek help. Common symptoms include sharp, cramping pain in the back, side, or lower abdomen, often coming in waves. Nausea, vomiting, painful urination, and blood in the urine are also frequent indicators.
For pain management, drinking plenty of water (up to 2-3 liters daily) can help flush the urinary system and encourage stone movement. Over-the-counter pain relievers can alleviate discomfort, though ibuprofen should be used cautiously during an acute attack if underlying health conditions exist. A healthcare provider might also prescribe medications, such as alpha-blockers, to help relax the ureter and facilitate stone passage.
It is important to seek immediate medical attention if certain warning signs appear. These include severe, unmanageable pain, fever and chills, persistent nausea and vomiting, or an inability to urinate. These symptoms could indicate a serious blockage or infection requiring prompt intervention. If possible, capturing the passed stone for analysis can help determine its composition, which is valuable for preventing future stones.