Kidney Stones: Getting Through One, and Not Getting Another
Kidney stone pain is routinely described as among the worst pain people experience. The acute episode gets attention; prevention usually does not, which is why recurrence rates are high.
What a stone is
Urine carries dissolved minerals. When concentration rises beyond what can stay dissolved, crystals form and aggregate into stones.
Calcium oxalate accounts for the majority. Calcium phosphate is next. Uric acid stones form in persistently acidic urine, and are associated with gout, obesity and diabetes. Struvite stones form in the presence of certain urinary infections and can grow large. Cystine stones are rare and genetic.
Knowing the type changes prevention substantially, which is why catching the stone matters.
The pain
Renal colic comes from the stone obstructing the ureter, the tube from kidney to bladder, causing pressure to build.
Typical features: sudden severe pain in the flank or loin, often radiating to the groin or testicle, coming in waves, with restlessness because no position helps, frequently with nausea and vomiting, sometimes with blood in the urine and urinary urgency as the stone nears the bladder.
The restlessness is characteristic. Someone with peritonitis lies very still; someone with renal colic cannot stay still.
Pain relief that works
NSAIDs are more effective than opioids for renal colic in trials, because they reduce the ureteric pressure as well as the pain. Diclofenac or ketorolac are commonly used. They are avoided in kidney impairment, so this is a medical decision, not a self-treatment instruction.
The old advice to drink large volumes of water during an acute episode is not supported; it increases pressure behind an obstruction and worsens pain.
Which stones pass by themselves
Size is the main predictor.
- Under 5 mm: a large majority pass spontaneously
- 5 to 10 mm: roughly half
- Over 10 mm: unlikely without intervention
Position matters too; stones in the lower ureter pass more readily.
Medical expulsive therapy with an alpha blocker such as tamsulosin is sometimes used to help passage of larger lower-ureteric stones.
Procedures when needed: shock wave lithotripsy, which breaks the stone externally; ureteroscopy with laser fragmentation; and percutaneous nephrolithotomy for large stones.
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When it is an emergency
Most colic is managed as an outpatient. These features are not:
- Fever or chills with the pain, suggesting an infected obstructed kidney, which is a urological emergency
- A single kidney, or a transplanted kidney
- Inability to keep fluids down
- Uncontrolled pain despite medication
- No urine output
- Signs of sepsis
An obstructed, infected kidney can deteriorate rapidly and needs urgent drainage.
Catching the stone
Strain your urine during an episode and keep what you catch. Stone analysis tells you the type, which determines prevention. This simple step is skipped constantly and makes the difference between generic advice and targeted advice.
Prevention that works
Fluid, properly. The single most effective measure. Aim for urine output of around 2.5 litres a day, which usually means drinking around three litres. Judge by urine colour, which should be pale. Spread intake across the day and include some before bed, since overnight concentration is when stones form.
Do not cut dietary calcium. This is the most common and most counterproductive mistake. Low dietary calcium increases oxalate absorption from the gut and raises stone risk. Normal dietary calcium, taken with meals so it binds oxalate in the intestine, is protective. Calcium supplements taken separately from food are a different matter and may increase risk.
Reduce sodium. High salt increases calcium excretion in urine directly.
Moderate animal protein. High intake increases calcium and uric acid excretion and lowers citrate.
Citrate. Citrate inhibits stone formation. Lemon and lime juice are useful dietary sources, and potassium citrate is prescribed for some stone formers.
Oxalate awareness, selectively. For calcium oxalate stone formers with high urinary oxalate, high-oxalate foods such as spinach, beetroot, nuts, rhubarb, chocolate and strong tea are worth moderating, ideally eaten with a calcium source. Blanket oxalate restriction is unnecessary for most.
Weight management, since obesity and insulin resistance raise risk, particularly for uric acid stones.
For uric acid stones, alkalinising the urine is the key measure, along with reducing purine-rich foods and treating gout.
The metabolic workup
After a second stone, or a first in someone young, with a family history, with a single kidney, or with an unusual stone type, a 24-hour urine collection measuring volume, calcium, oxalate, citrate, uric acid, sodium and pH identifies the specific abnormality driving stone formation and allows targeted treatment.
Most recurrent stone formers have never had this done, which is why so much prevention advice stays generic.
The short version
Strain and keep the stone, because the type determines the plan. Drink enough that your urine stays pale, cut salt, keep dietary calcium normal rather than low, and if you have had more than one stone, ask for a 24-hour urine study instead of another round of general advice.