Also known as: Nephrolithiasis (Renal Calculi)
Kidney stones are hard deposits of minerals and salts that form inside the kidneys.
Kidney stones (nephrolithiasis) are one of the most common disorders of the urinary tract, affecting approximately 1 in 11 people in the United States during their lifetime. The prevalence has been rising steadily over the past several decades, likely due to changes in diet, increasing obesity rates, and climate change. Kidney stones form when the urine becomes supersaturated with certain minerals and salts, which crystallize and aggregate into solid masses within the kidney. The four main types of kidney stones are calcium oxalate (the most common, comprising about 70-80% of stones), calcium phosphate, uric acid, and struvite (infection-related) stones.
Small kidney stones may pass through the urinary tract without causing symptoms. However, when a stone moves from the kidney into the ureter (the narrow tube connecting the kidney to the bladder), it can obstruct urine flow and cause one of the most intense pain experiences known in medicine — renal colic. The pain typically begins suddenly, radiates from the flank to the lower abdomen and groin, and fluctuates in intensity as the ureter contracts to push the stone forward. This pain is frequently compared to or rated as more severe than childbirth, bone fractures, or gunshot wounds.
The likelihood of passing a stone spontaneously depends primarily on its size. Stones smaller than 5mm have an approximately 80% chance of passing on their own, while stones larger than 8mm typically require medical or surgical intervention. Kidney stones have a high recurrence rate — without preventive measures, approximately 50% of patients will develop another stone within 5-10 years. A thorough metabolic evaluation and individualized prevention strategy are essential for reducing recurrence risk. Identifying the stone type through analysis is critical for guiding dietary and medical prevention strategies.
People with Kidney Stones often experience the following symptoms.
The hallmark symptom is sudden, excruciating pain in the side and back, just below the ribs. The pain is caused by the stone obstructing the ureter, leading to increased pressure in the kidney and ureteral spasm. The pain comes in waves (colicky), with intense peaks lasting 20-60 minutes followed by brief periods of relative relief.
As the stone moves down the ureter, the pain typically migrates. Upper ureteral stones cause flank pain, mid-ureteral stones radiate to the lower abdomen, and distal ureteral stones cause pain in the groin, inner thigh, or genital area (testicle in men, labia in women). This pain migration often indicates the stone is progressing.
Blood in the urine, which may be visible (gross hematuria producing pink, red, or brown urine) or detectable only by urinalysis (microscopic hematuria), occurs in approximately 85% of patients with kidney stones. The stone's rough edges scratch the delicate lining of the urinary tract as it moves.
The severe pain from renal colic frequently triggers nausea and vomiting through shared nerve pathways between the kidneys and the gastrointestinal tract (renointestinal reflex). This can complicate management by preventing oral hydration and medication intake.
When the stone reaches the lower ureter near the bladder, it can mimic UTI symptoms including burning during urination, increased urinary frequency, and urgency. Patients may feel an intense need to urinate with only small amounts of urine produced.
Unlike many other abdominal conditions where patients prefer to lie still, kidney stone patients are characteristically restless, constantly shifting positions and pacing in an attempt to find relief. This restless behavior is an important clinical clue for diagnosis.
Fever accompanying a kidney stone is a concerning sign that suggests concurrent urinary tract infection (infected obstructing stone). This combination represents a urological emergency requiring urgent decompression, as infected urine trapped behind an obstructing stone can rapidly lead to urosepsis.
Certain factors may increase your likelihood of developing Kidney Stones.
Common approaches to managing kidney stones. Always consult a healthcare provider for personalized treatment.
Small stones (less than 5-6mm) are often managed conservatively with aggressive hydration (2-3 liters of water daily), pain control with NSAIDs (ketorolac, ibuprofen) and acetaminophen, and anti-nausea medications. Medical expulsive therapy with tamsulosin (an alpha-blocker) relaxes the ureteral smooth muscle and can facilitate stone passage, particularly for distal ureteral stones.
ESWL uses focused shock waves delivered from outside the body to break kidney stones into smaller fragments that can pass naturally through the urinary tract. It is most effective for stones less than 2cm located in the kidney or upper ureter. The procedure is performed under sedation and is non-invasive, though multiple sessions may be needed.
A flexible ureteroscope is passed through the urethra and bladder into the ureter to directly visualize and fragment the stone using a holmium laser. Stone fragments are then removed with a basket device. This is the preferred approach for mid and distal ureteral stones and is effective for stones of most compositions and sizes up to 2cm.
For large kidney stones (greater than 2cm), staghorn calculi, or stones resistant to ESWL, PCNL is performed by creating a small channel through the skin and into the kidney. Specialized instruments are used to fragment and remove the stone. This procedure offers the highest stone-free rates for large stones but requires general anesthesia and a short hospital stay.
Prevention is critical given the high recurrence rate. General measures include drinking 2.5-3 liters of fluid daily (enough to produce over 2 liters of urine), reducing sodium intake, consuming adequate dietary calcium (not supplements), limiting animal protein, and increasing citrus fruit intake. Specific medications such as potassium citrate, thiazide diuretics, or allopurinol may be prescribed based on stone composition and metabolic evaluation results.
An obstructing stone with concurrent infection (fever, positive urine culture) is a urological emergency. Urgent drainage of the infected, obstructed kidney is performed either by placing a ureteral stent (passed retrograde through the bladder) or a percutaneous nephrostomy tube (placed through the skin into the kidney). Definitive stone treatment is deferred until the infection is controlled.
Kidney stone diagnosis typically begins when a patient presents with acute flank pain. A non-contrast CT scan of the abdomen and pelvis is the gold standard imaging study, offering sensitivity and specificity above 95% for detecting stones of all compositions and sizes. The CT also identifies the stone's location, size, and the degree of urinary obstruction (hydronephrosis). Ultrasound is preferred as an initial study in pregnant women and children to avoid radiation exposure. Urinalysis reveals hematuria in most cases and can detect concurrent infection. Basic blood work including a complete metabolic panel assesses kidney function, calcium levels, and uric acid. When a stone is passed or surgically retrieved, compositional analysis is essential for guiding prevention strategies. For patients with recurrent stones, a 24-hour urine collection measures calcium, oxalate, citrate, uric acid, sodium, and volume to identify specific metabolic risk factors driving stone formation.
Seek immediate medical care if you experience pain so severe you cannot sit still or find a comfortable position, pain accompanied by high fever and chills, blood in your urine, difficulty passing urine, or persistent nausea and vomiting preventing fluid intake.
Steps that may help reduce the risk of developing or worsening kidney stones.
Drink enough fluids daily (at least 2.5-3 liters) to produce more than 2 liters of urine per day, with water being the best choice
Reduce dietary sodium intake to less than 2,300 mg per day, as excess sodium increases urinary calcium excretion and stone risk
Consume adequate dietary calcium from food sources (dairy, leafy greens) rather than supplements, as dietary calcium binds oxalate in the gut and reduces absorption
Limit intake of animal protein (meat, poultry, fish) which increases urinary calcium, oxalate, and uric acid while reducing protective citrate
Increase intake of fruits and vegetables, particularly citrus fruits, which provide citrate — a natural stone inhibitor that prevents crystal formation
If left untreated or poorly managed, kidney stones may lead to:
The time to pass a kidney stone depends primarily on its size and location. Stones smaller than 4mm typically pass within 1-2 weeks. Stones between 4-6mm may take 2-6 weeks and have about a 60% chance of passing spontaneously. Stones larger than 6mm have a significantly lower spontaneous passage rate and often require intervention. Drinking plenty of water, staying active, and using prescribed medications like tamsulosin can help facilitate passage.
Kidney stone pain (renal colic) is frequently described as one of the most intense pain experiences possible. It typically begins suddenly in the flank (side and back below the ribs) and radiates to the lower abdomen and groin. The pain is colicky, coming in severe waves lasting 20-60 minutes. Patients often cannot find a comfortable position and may pace or writhe. The pain is caused by the stone obstructing the ureter, creating pressure buildup and ureteral spasm.
Dietary recommendations depend on your stone type. For calcium oxalate stones (the most common), limit high-oxalate foods including spinach, rhubarb, beets, nuts, chocolate, and sweet potatoes. Reduce sodium intake as excess salt increases urinary calcium. Limit animal protein which raises uric acid and calcium while lowering citrate. Importantly, do NOT restrict dietary calcium — adequate calcium from food actually reduces stone risk by binding oxalate in the gut. Increase fluid intake and citrus consumption.
Genetics play a significant role in kidney stone formation. Having a first-degree relative with kidney stones approximately doubles your risk. Specific genetic conditions such as cystinuria, primary hyperoxaluria, and renal tubular acidosis directly cause stone formation. More commonly, genetic factors influence how your body handles calcium, oxalate, and other minerals. However, environmental and dietary factors also play major roles, meaning that even with a genetic predisposition, preventive measures can significantly reduce your risk of stone formation.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.