Nephrolithiasis is the medical term for kidney stones. The word comes from the Greek “nephro” (kidney) and “lithos” (stone). If you saw this term on a medical report or heard it from a doctor, it simply means that one or more solid mineral deposits have formed inside your kidney. You may also see it written as “renal calculus” or “urolithiasis,” which all describe the same condition.
Kidney stones affect 10% to 15% of the global population, and the lifetime risk in industrialized countries exceeds 12% for men and 6% for women. Understanding what the term means is the easy part. Knowing how stones form, what they feel like, and what happens next is what most people actually need.
How Kidney Stones Form
Your kidneys filter waste products from your blood and flush them out in urine. That urine contains dissolved minerals and salts, primarily calcium, oxalate, and uric acid. When the concentration of these substances gets too high relative to the amount of liquid, they can crystallize. Think of it like dissolving sugar in water: add too much and it starts forming crystals at the bottom of the glass.
Your urine naturally contains substances that inhibit crystal formation, which is why most people don’t develop stones even when mineral concentrations rise temporarily. But when those protective factors are overwhelmed, or when urine stays concentrated for too long, tiny crystals can form in the deep structures of the kidney. Over time, these crystals anchor to the kidney’s inner lining, accumulate more mineral layers, and grow into a stone.
About 80% of kidney stones are calcium-based, mostly calcium oxalate. The remaining 20% include uric acid stones, infection-related stones (called struvite), and rare genetic types like cystine stones. The composition matters because it determines both what caused the stone and how it’s treated.
What Nephrolithiasis Feels Like
A kidney stone sitting quietly inside the kidney often causes no symptoms at all. Many people have small stones and never know it. The trouble starts when a stone moves out of the kidney and enters the ureter, the narrow tube connecting the kidney to the bladder.
When a stone gets stuck in the ureter, it blocks urine flow. The kidney swells, the ureter spasms, and the result is one of the most intense pains people describe experiencing. This pain, called renal colic, typically hits suddenly in the side and back just below the ribs. It can radiate to the lower abdomen and groin. The pain often comes in waves as the ureter contracts, trying to push the stone through.
Other common symptoms include blood in the urine (which may look pink, red, or brown), nausea, vomiting, fever, and chills. Fever with a kidney stone can signal an infection, which requires urgent attention.
Risk Factors That Drive Stone Formation
The single biggest modifiable risk factor is not drinking enough fluid. When urine volume drops, mineral concentrations rise, and the chance of crystallization increases. But several metabolic factors also play a role.
High calcium excretion in urine is one of the strongest predictors. Research on families with this trait shows the risk of forming stones rises progressively as urinary calcium levels climb. High uric acid excretion is another independent risk factor, often reflecting a diet heavy in animal protein. Age matters too, likely because the longer your kidneys are exposed to elevated mineral concentrations, the more opportunity stones have to form.
Other well-established risk factors include obesity, a diet high in sodium (which increases calcium in the urine), chronic dehydration from climate or occupation, and a personal or family history of stones. Certain medical conditions like gout, inflammatory bowel disease, and parathyroid disorders also raise risk significantly.
How Kidney Stones Are Diagnosed
If you show up with flank pain and suspected kidney stones, a non-contrast CT scan is the gold standard for diagnosis. It can detect stones of nearly any size and composition, with sensitivity and specificity above 90% for patients at a healthy weight. For people with a BMI over 30, a standard-dose scan is used because low-dose images lose accuracy in larger body types.
Ultrasound is preferred over CT in two situations: children (to avoid radiation exposure) and pregnant women. For people who have had stones before and know their stones show up on X-ray, a combination of ultrasound and a plain abdominal X-ray can be enough to track recurrence without repeated CT scans.
Will the Stone Pass on Its Own?
This depends almost entirely on size. Smaller stones have a good chance of passing through the urinary tract without intervention, though the process can take days to weeks and is often painful.
Here’s how size affects the odds:
- 1 to 4 mm: About 72% to 87% pass spontaneously
- 5 to 6 mm: About 60% to 72% pass spontaneously
- 7 to 9 mm: About 33% to 48% pass spontaneously
- 10 mm or larger: Only about 25% to 27% pass on their own
While waiting for a stone to pass, treatment focuses on pain control and hydration. Your doctor may also prescribe a medication that relaxes the ureter walls, helping the stone move through more easily. You’ll likely be asked to strain your urine so the stone can be caught and analyzed, since knowing what it’s made of guides prevention.
When Stones Need Procedures
Stones roughly 7 mm and larger that aren’t passing on their own typically need a procedure. The options depend on the stone’s size and location.
Shockwave lithotripsy uses focused sound waves from outside the body to break a stone into smaller fragments that can then pass naturally. It works best for stones in the kidney or upper ureter that are not too large or too hard. Ureteroscopy involves passing a thin scope up through the bladder and ureter to reach the stone directly, where it can be broken apart with a laser and removed in fragments. This approach works well for mid-sized stones in the ureter.
For large stones over 2 cm, a procedure called percutaneous nephrolithotomy is typically recommended. A small incision is made in the back, and a scope is passed directly into the kidney to break up and remove the stone. Recovery takes longer than the other options, but it’s the most effective approach for big or complex stones. Open surgery is rarely needed anymore.
Preventing Stones From Coming Back
Kidney stones recur frequently. Without changes, many people who form one stone will form another. The most effective prevention strategy is also the simplest: drink enough fluid to produce at least 2.5 liters of urine per day. The NHS recommends aiming for up to 3 liters of fluid daily, spread throughout the day. Water is ideal, and a good rule of thumb is that your urine should be pale yellow or nearly clear.
Dietary adjustments depend on the type of stone you formed. For calcium oxalate stones (the most common), reducing sodium intake helps because excess salt drives calcium into the urine. Eating moderate amounts of calcium from food, rather than avoiding it, actually binds oxalate in the gut and reduces the amount that reaches the kidneys. Limiting animal protein lowers uric acid levels. For uric acid stones specifically, reducing purine-rich foods like red meat, organ meats, and shellfish can make a meaningful difference.
If you’ve had a stone analyzed and your doctor has identified a specific metabolic abnormality through a 24-hour urine collection, targeted prevention becomes possible. The goal is always the same: keep urine dilute and reduce the concentration of whatever mineral formed the stone in the first place.