Kidney stones
A kidney stone is a hard lump of crystals that grows in urine the way salt drops out of a saturated solution.
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Medicines commonly prescribed for Kidney stones
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: TABLET, 600 mgActive substance: ibuprofenManufacturer: Industria Quimica Y Farmaceutica Vir S.A.Prescription requiredDosage form: ORAL SOLUTION/SUSPENSION, 40 mg/mlActive substance: ibuprofenManufacturer: Kern Pharma S.L.Prescription not requiredDosage form: TABLET, 400 mgActive substance: ibuprofenManufacturer: Zambon S.A.U.Prescription not required
A kidney stone is a hard lump of crystals that grows in urine the way salt drops out of a saturated solution. While it sits in the kidney it usually causes nothing at all. The pain starts when it shifts and lodges in the ureter, the few-millimetre tube that carries urine down to the bladder. About one person in ten forms a stone at some point in life, more often men and most often between thirty and sixty. What is dangerous is not the stone itself but a blocked ureter: with infection behind it this becomes an emergency measured in hours, and when it blocks painlessly it can quietly destroy a kidney within weeks.
What a stone feels like
Small stones pass unnoticed and turn up by chance on a scan done for something else. The attack known as renal colic is unmistakable. The pain comes on abruptly, often at night or towards morning, in the loin or the flank on one side, and arrives in waves: half an hour of the unbearable, then it eases, then it returns. The giveaway is that the person cannot lie still. They pace, shift position, and nothing gives relief. With problems inside the abdomen it is the other way round and the patient keeps as still as possible.
As the stone travels down, the pain moves with it into the groin, radiating to the testicle in men and the labia in women. There is nearly always nausea and often vomiting. Urine may turn pink, though more often the blood shows only under the microscope, and in roughly one case in ten there is no blood at all. Once the stone reaches the entrance to the bladder, urgency and stinging join in and the whole thing is easily mistaken for cystitis. The severity of the pain says nothing about size: a two-millimetre fragment in an awkward spot takes a person out of action, while a large stone lying quietly in the renal pelvis does not hurt at all.
When it cannot wait until morning
Call an ambulance if fever and shivering join the flank pain, the kind of shaking where it is impossible to get warm. That combination means infected urine has collected behind a blocked ureter. Antibiotics alone do not rescue this: pus under pressure has to be drained through a tube, and it has to be done within hours, or sepsis follows. Confusion, rapid shallow breathing, cold mottled skin and a falling blood pressure need the same immediate response.
You should be seen the same day if the pain does not settle with a painkiller, if vomiting stops you keeping down water or tablets, if urine stops altogether, and also if you have a single kidney or a transplanted one, in which case any attack is assessed in hospital.
One mistake deserves separate mention because it costs lives. Severe flank pain appearing for the first time after the age of fifty, particularly in a smoker with high blood pressure, is not necessarily colic. A leaking abdominal aortic aneurysm begins the same way and is regularly taken for a stone. If the pain comes with weakness, fainting, pallor or a pulsating sensation in the abdomen, this is emergency surgery rather than a urinary problem.
Stones are not all the same
The composition determines both how a stone is removed and how the next one is prevented. That is why a stone you pass should not be thrown away but sent for analysis.
- Calcium stones make up around three quarters of cases, more often oxalate and less often phosphate. They are dense and show up well on imaging.
- Uric acid stones grow in persistently acid urine and keep company with gout, obesity and diabetes. They are invisible on a plain X-ray, but they are the only ones that can sometimes be dissolved with medication.
- Infection (struvite) stones are built by bacteria that break down urea. They grow fast and within months can fill the whole collecting system, taking the shape of a stag's antlers. Such a stone is removed complete, because any fragment left behind carries the organisms inside it and the whole thing starts again.
- Cystine stones are uncommon and follow an inherited defect of the kidney tubules. They announce themselves in childhood or youth and keep returning for life, so these patients are looked after by a specialist.
What pushes a kidney into making them
The main cause is the same for every type: not enough fluid. Concentrated urine is a saturated solution, and crystals need only the slightest foothold. Hence the seasonality: in hot weather, in outdoor work and in people who sweat heavily, stones appear noticeably more often. Then come habits. Salt makes the kidney put more calcium into the urine, meat raises urinary acidity and uric acid while leaving less of the protective citrate, and sugary fizzy drinks push the same way. Obesity, diabetes and gout raise the risk in their own right, and a family history doubles it.
Some causes are worth hunting for because they have treatment of their own: primary hyperparathyroidism, with a persistently raised blood calcium; bowel disease, extensive bowel resection and weight-loss surgery, after which too much oxalate is absorbed; chronic diarrhoea; renal tubular acidosis; and anatomical variations that obstruct the flow of urine. Long immobility after an injury belongs on the list too.
Medicines are worth stating precisely, because there is confusion about them. The risk is raised by loop diuretics, acetazolamide and topiramate, excessive calcium and vitamin D supplements, certain antibiotics and antiviral drugs, and laxative abuse. Thiazide diuretics do the opposite: they are prescribed precisely to stop stones forming again. Aspirin has nothing to do with stone formation.
Finding the stone
Urine testing almost always shows red cells, while nitrites and white cells mean infection has joined in. Blood tests cover creatinine to judge kidney function, along with calcium and urate, and if infection is suspected, a full blood count and C-reactive protein.
The stone itself is shown by low-dose non-contrast computed tomography, which finds stones of any composition and gives the size, the exact position and the signs of obstruction; this is the scan adults have in an acute attack. In pregnancy and in children ultrasound comes first because it involves no radiation, and computed tomography is used only if there is no way round it.
If this is not your first stone, if it appeared at a young age, or if you have one kidney or stones in both, the work continues with a twenty-four-hour urine collection measuring volume, acidity, calcium, oxalate, citrate and urate, plus parathyroid testing if the blood calcium is high. Without that, prevention is guesswork.
The attack and passing the stone
Colic pain responds best to non-steroidal anti-inflammatory drugs, which in this situation outperform opioids. They do not suit everyone, though: with reduced kidney function, a history of ulcers, anticoagulant treatment or in older age, paracetamol is chosen instead, and stronger drugs are added in hospital if needed. Something for the nausea is prescribed separately. The doctor decides the regimen, because both the state of the kidney and whatever you already take matter here.
The advice to drink a great deal to flush the stone out does not work during an attack and may do harm, since pressure behind the blockage is already rising. Drink as much as you want, and save the generous fluid intake for prevention. For stones in the lower ureter a doctor sometimes adds an alpha blocker, which relaxes that stretch of wall.
After that it is a question of size. Stones under five millimetres nearly always pass on their own, those between five and ten millimetres do so about half the time, and larger ones rarely. It takes anything from a few days to a little over a month. Pass your urine through a sieve during this period so the stone can be caught and analysed.
The most important rule sounds counter-intuitive: pain stopping does not mean the stone has gone. The ureter can remain blocked while the kidney behind it gradually shuts down without giving any sign. That is why imaging is repeated after the attack to confirm the drainage is clear.
When the stone is removed
Intervention is needed if the stone is too big, if it has not passed within the expected time, if the pain cannot be controlled, if kidney function is falling, or if the kidney is a solitary one. With infection behind a blockage the order changes: drainage is restored urgently first, either with an internal stent or a tube through the skin, and the stone is dealt with later once the infection has settled.
- Extracorporeal shock wave lithotripsy. A machine focuses shock waves on the stone from outside and breaks it into grit that then passes in the urine. General anaesthetic is not usually needed, but several sessions are sometimes required, and the fragments can line up temporarily in the ureter and set off a fresh attack.
- Ureteroscopy. A fine telescope is passed through the urethra and bladder to the stone, which is broken up with a laser and the pieces retrieved. This gives the most predictable result in a single procedure. A temporary stent is often left afterwards, causing a few days of urinary urgency, discomfort and blood in the urine: this is expected and settles once it comes out.
- Percutaneous nephrolithotomy. Instruments are passed into the kidney through a small puncture in the back and the stone is removed whole or in pieces. This is the route for large and staghorn stones. It needs a general anaesthetic and a few days in hospital.
Any of these can have complications: bleeding, infection up to sepsis, injury to the ureter, residual fragments. Open surgery is rare nowadays, and uric acid stones sometimes need no procedure at all, being dissolved by making the urine alkaline.
Not growing the next one
About half of people have another stone within five to ten years, and this is one of those situations where prevention genuinely changes the odds.
- Drink enough to produce around two and a half litres of urine a day, and more in heat or with exercise. Spread it across the day and have some before bed, because urine is at its most concentrated overnight. The marker is a pale straw colour.
- Add lemon or lime juice to water: citrate binds calcium in the urine and stops crystals growing. Sugary lemonade does not do this.
- Cut down salt, which for calcium stones is the single most effective dietary change, and moderate meat without giving up protein.
- Do not restrict dietary calcium. This is an old and harmful mistake: calcium in food binds oxalate inside the bowel itself, and without it more oxalate is absorbed and more stones form, not fewer. Dairy is eaten as normal. Caution applies only to calcium tablets, particularly if taken away from meals.
- High-oxalate foods such as spinach, rhubarb, beetroot, nuts, chocolate and strong tea are not restricted for everyone, only for people with proven oxalate stones and a high urinary oxalate. Even then it is usually enough to eat them alongside something dairy.
- With uric acid stones, red meat, offal, seafood and beer are reduced and the urine is made alkaline with citrate, sometimes with a drug that lowers uric acid production added.
- With calcium stones and a high urinary calcium, a thiazide diuretic is prescribed.
- Losing weight and moving regularly work in the same direction.
Notice that the last few points contradict one another: what helps with one type of stone is useless with another. So changing your diet blind is not worth it. The stone's composition and the twenty-four-hour urine come first, the diet after.
Online consultation
In an online consultation the doctor will work out whether your pain fits renal colic and whether there are signs that mean going to hospital without waiting. They will say which tests and which scan to arrange first, help you read images and reports you already have, and explain what to expect from a stone of your size and position. If stones keep coming back the conversation is a different one: which investigation will find the cause, whether a twenty-four-hour urine collection is worth doing, what to make of the analysis of a stone you have already passed, and how to build your drinking and eating around your particular stone type rather than around general advice from the internet.
This material is for information only and does not replace medical advice.
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Discuss your symptoms and possible next steps for Kidney stones with a doctor online.
