Kidney stones, medically known as nephrolithiasis, are hard deposits formed from minerals and salts that crystallize within the urinary tract. These masses typically develop in the kidneys when the concentration of substances like calcium, oxalate, and uric acid becomes too high in the urine. While small stones may pass unnoticed, a larger stone can cause significant symptoms if it attempts to move from the kidney into the narrow tubes called the ureters. Stone size is the single most important factor determining the potential for spontaneous passage and the subsequent course of treatment.
Why Stone Size Matters: The 5 mm Threshold
The 5-millimeter size represents a recognized threshold in urology for predicting the likelihood of a stone passing without invasive procedures. Stones smaller than 5 mm have a high chance of spontaneous passage, often cited in the range of 65% to over 80%. Stones larger than 5 mm have a significantly lower chance of passing naturally, with the rate dropping considerably for stones measuring 6 mm and above.
A 5-millimeter stone is on the cusp of requiring intervention, but it is still commonly managed conservatively. The stone’s exact location within the ureter is also a strong predictor of passage; stones in the lower, or distal, section have a greater probability of passing than those lodged higher up. Since natural passage is still favorable for a 5 mm stone, the initial strategy is almost always observation and medical support to facilitate its journey down the ureter.
Symptoms and Diagnostic Imaging
The primary symptom associated with a 5-millimeter stone moving through the urinary tract is renal colic, a severe, cramp-like pain. This intense sensation comes in waves lasting 20 to 60 minutes as the ureter walls contract to push the stone along. The pain typically originates in the flank or lower back and often radiates downward to the abdomen and groin area as the stone descends.
Other common signs include hematuria (blood in the urine), which may make the urine appear pink, red, or brown. The irritation and obstruction caused by the stone can also lead to secondary symptoms such as nausea, vomiting, and a frequent or urgent need to urinate.
To confirm the stone’s presence, size, and precise location, diagnostic imaging is necessary. A non-contrast computed tomography (CT) scan is often considered the gold standard for its high sensitivity and ability to accurately measure the stone’s diameter.
An ultrasound may be used as a first-line imaging choice to avoid radiation exposure. Ultrasound uses sound waves to visualize the kidneys and ureters, and it is particularly good at showing hydronephrosis, which is swelling of the kidney caused by blocked urine flow. For a 5 mm stone, the exact measurement provided by a CT scan is important to guide the decision between conservative management and aggressive intervention.
Conservative Management and Home Care
For a 5-millimeter stone, the initial treatment plan focuses on promoting natural passage and managing pain. Aggressive hydration is a cornerstone of home care, requiring significantly increased fluid intake, often aiming for a urine output of more than two liters per day. Maintaining pale, clear urine increases the flow and pressure behind the stone, encouraging movement.
Pain management is achieved using non-steroidal anti-inflammatory drugs (NSAIDs) to control inflammation and renal colic pain. Stronger prescription pain medication may be provided for intense pain.
Medical expulsion therapy (MET) is often prescribed to help the process along. This therapy involves alpha-blockers, which relax the smooth muscles of the ureter. By widening the tube, these medications make it easier for the 5 mm stone to pass.
Alpha-blockers increase the stone expulsion rate, particularly for stones in the 5-to-10-millimeter range, and may reduce the need for surgical intervention. Patients are also advised to strain their urine using a filter to capture the stone once it passes. This allows for laboratory analysis to determine its chemical composition, which is important for tailoring long-term preventive strategies.