Kidney stones are hard, solid masses formed from the crystallization of minerals and salts within the kidney. These deposits, often composed of calcium oxalate, uric acid, or other compounds, can range in size from a grain of sand to a small pebble. When these stones move out of the kidney, they must exit the body through the urinary system. The direct answer to the question is that you cannot “poop out” a kidney stone; they are passed through the urinary tract, not the digestive tract.
The Urinary Tract Pathway
The urinary tract is the specific route a kidney stone must travel to leave the body, entirely separate from the gastrointestinal system. Urine is created in the kidneys and then flows down two narrow tubes called the ureters, which connect the kidneys to the bladder.
When a stone dislodges from the kidney, it enters the ureter, a tube typically only 3 to 4 millimeters (mm) in diameter, which is where most problems occur. Stones smaller than 4 mm have the highest chance of passing spontaneously, often within a few weeks. The stone’s movement down this narrow tube is what triggers the severe pain associated with a stone passage.
From the ureter, the stone drops into the bladder. At this point, the intense, cramping pain often subsides, replaced by a feeling of pressure. Finally, the stone is expelled from the body through the urethra during urination. The process always follows this specific path through the urinary system.
Symptoms Experienced During Passage
The most recognizable symptom of a kidney stone is renal colic, a severe, cramping pain caused by the stone blocking the flow of urine and causing the ureter to spasm. This pain typically begins suddenly in the flank—the side and back just below the ribs. The pain is not constant but comes in intense waves as the ureteral muscle contracts around the stone.
As the stone moves lower down the ureter toward the bladder, the location of the pain often shifts, radiating forward to the lower abdomen and groin area. Patients may also experience nausea and vomiting, a secondary discomfort often attributed to the shared nervous system pathways between the urinary and gastrointestinal tracts.
When the stone nears the bladder, it can cause lower urinary tract symptoms that mimic a urinary tract infection. These include an increased urgency and frequency of urination, as well as a burning sensation during voiding, known as dysuria. Hematuria, or blood in the urine, is also common as the stone scrapes the lining of the urinary tract walls, causing the urine to appear pink, red, or brown.
Next Steps After Passing a Stone
Once the stone is expelled, the pain usually resolves, but several follow-up steps are necessary. You will likely be instructed by your healthcare provider to strain your urine using a special stone collection filter until the stone or fragments are retrieved. The stone needs to be analyzed in a laboratory to determine its chemical composition, such as calcium oxalate, uric acid, or struvite.
Collecting the stone is important because the analysis results dictate the specific dietary and medical changes needed to prevent future episodes. For instance, a uric acid stone requires different prevention strategies than a calcium stone. After collection, the stone should be dried and placed in a clean, dry container to be taken to your doctor’s office.
It is important to seek immediate medical attention if you experience certain signs, even after you believe the stone has passed. A fever over 100.4°F (38°C) accompanied by chills, or an inability to urinate, can indicate a serious complication such as an infection behind an obstruction. These symptoms suggest a medical emergency requiring rapid intervention, such as antibiotics and potential drainage of the kidney.