How Kidney Stones Form and How to Prevent Them

Urine carries the minerals the body needs to excrete, dissolved in water. While the urine is dilute enough, those minerals stay dissolved. When it becomes concentrated the limit of solubility is passed: the minerals first precipitate as microscopic crystals, and those crystals then stick together to form a stone.

That is why stone disease rarely has a single culprit. Drinking too little, losing fluid through sweat, too much salt, excess animal protein, certain medicines, chronic diarrhoea and some metabolic conditions all contribute to the same result by different routes.

A stone does not form suddenly; it develops over months. The practical meaning of that is simple: if nothing changes after you pass a stone, the same conditions carry on producing new ones.

The commonest type is calcium oxalate. Uric acid stones, infection-related (struvite) stones, cystine stones and stones caused by certain drugs are less common.

The type matters because PREVENTION DEPENDS ON IT. In uric acid stones, making the urine less acidic can contribute to dissolving the stone, whereas the approach in calcium oxalate stones is different. An infection stone will keep growing unless it is cleared completely.

So DO NOT THROW AWAY the stone you pass or that is removed. Stone analysis is the cheapest test that shapes the plan for years to come.

The typical complaint is severe pain coming in waves from the loin to the groin (renal colic). Nausea, vomiting, blood in the urine and frequency can accompany it.

THIS IS AN EMERGENCY: flank pain TOGETHER WITH fever or shivering. It can mean infection in an obstructed kidney, and that can become a serious situation within hours. Waiting to see whether it settles is not right; go to hospital immediately.

AN IMPORTANT MISCONCEPTION: the absence of pain does not mean you are safe. A slowly developing obstruction can quietly reduce kidney function without causing pain. A follow-up appointment is therefore not skipped because "the pain has gone".

Inability to pass urine, colic in someone with a single kidney, and vomiting that cannot be controlled also require assessment without delay.

The first step is urinalysis, blood tests including kidney function, and imaging. Ultrasound involves no radiation and is the first choice particularly in pregnancy and in children.

A non-contrast CT scan shows the position, size and density of the stone most clearly, and the treatment plan is often based on it. A CT is not needed at every review, however; the radiation burden is not increased without reason.

The urine culture must be clear before treatment is planned. Intervening on a stone while an infection is present raises the risks markedly.

The single most effective measure in stone disease is drinking enough to increase the volume of urine. The aim is a markedly higher daily urine output, and the practical sign of that is pale urine.

If you live in a hot climate, do physical work or sweat a great deal, your requirement is higher. Every day you fail to replace what you lose, your urine becomes more concentrated.

The night matters too: urine concentrates during sleep. Getting up once at night to drink is advised for some patients.

Replacing water with sugary drinks is not protective; sugar- and fructose-sweetened drinks can increase the risk.

SALT: excess salt increases the calcium excreted in the urine and makes stone formation easier. Reducing salt is a far sounder step than cutting out calcium.

ANIMAL PROTEIN: excessive meat raises the acidity of the urine and increases the risk of both uric acid and calcium stones. The aim is not to cut protein out but to avoid excess.

OXALATE: spinach, beetroot, nuts, chocolate and tea are rich in oxalate. A complete ban is not required; balancing the quantity and taking these foods together with a meal CONTAINING CALCIUM is more effective.

CALCIUM — THE COMMONEST MISTAKE: many people with stones cut out calcium. That is WRONG and can INCREASE the risk. Calcium taken in food binds oxalate in the bowel and reduces its absorption. Calcium should be taken in normal amounts from food; calcium supplements should not be used without medical advice.

CITRATE: lemons and citrus fruit raise citrate in the urine, and citrate makes crystallisation harder. Squeezing lemon into water is a simple and harmless support.

A more detailed assessment is needed where stones recur, where there is a single kidney, where stones began in childhood, where there is a family history, or where the stone type is unusual.

That assessment involves a 24-hour urine collection measuring volume, calcium, oxalate, citrate, uric acid and other parameters. The aim is to find out WHY the stone formed and to tailor prevention to the individual.

In some patients medication is added — for example drugs that make the urine less acidic or reduce calcium excretion. These are started under medical supervision and monitored with blood tests.

Some small, favourably placed stones pass on their own; pain control and, in some patients, medication that helps the stone pass are used during that time.

For stones that do not pass or that cause obstruction, the options are shock wave lithotripsy (ESWL), flexible ureteroscopy through the urinary passage (RIRS) and the percutaneous route through the skin into the kidney (PCNL). Which suits you depends on the size, position and hardness of the stone and on the anatomy of your kidney.

A stent (JJ) may be placed temporarily after the procedure. With a stent in place, frequency, urgency and slight bleeding are usual. WHO removes the stent, WHERE and WHEN must be planned before the procedure — this matters particularly for patients travelling from abroad.

Stone disease is not a one-off event but a condition with a tendency to recur. Someone who has passed one stone has a far from negligible chance of forming another over the years.

Treatment therefore does not end when the stone is removed. It continues with fluid intake, the balance of salt and protein, stone analysis and, where needed, metabolic assessment.

Regular review allows a silent stone to be noticed before it grows and obstructs. Ultrasound is usually sufficient for that follow-up and involves no radiation.

This article is for general information and does not replace medical advice. The management of stone disease is individual.

FLANK PAIN TOGETHER WITH FEVER OR SHIVERING IS AN EMERGENCY; go to hospital without delay.

"Herbal teas dissolve stones." The only group that can genuinely be dissolved is uric acid stones, and that is done by making the urine less acidic, under medical supervision. A calcium oxalate stone dissolves with no tea at all; delaying treatment on the strength of that claim can damage the kidney.

"I passed my stone, so that is the end of it." Passing a stone ends that episode, not the disease. If the conditions do not change, another will form.

"I should avoid calcium." No. Cutting dietary calcium can increase the risk; what should be reduced is salt and excess animal protein.

"If I have no pain, I have no stone." Silent stones exist, and slowly developing obstruction can be painless. Kidney function can decline without being noticed.

"Drinking a lot of water will flush the stone out." Fluid is the most effective measure for preventing new stones, but water cannot push out a stone that is already impacted, and where there is obstruction, drinking a great deal can increase the pain.