Renal colic (kidney stone pain): a case-based approach

The case: sudden severe pain in the side

A previously well adult wakes with severe pain that starts in one side of the lower back and grips round towards the groin. The pain comes in waves, so intense that they cannot sit still and keep pacing and shifting position. They feel sick and have vomited once. There is no fever. This picture — sudden, severe, colicky pain that moves from loin to groin and makes someone restless — is the classic story of renal colic. It is caused by a stone moving down the tube (the ureter) that carries urine from the kidney to the bladder. Unlike the pain of appendicitis, where people lie still, stone pain often makes people writhe.

Why kidney stones cause such pain

Kidney stones are hard lumps that form from minerals and salts in the urine. Many sit quietly in the kidney and cause no trouble. Pain begins when a stone drops into the ureter and blocks the flow of urine. The kidney keeps making urine, which backs up behind the blockage and stretches the system, and the ureter squeezes hard to try to push the stone along. This stretching and squeezing is what produces the severe, wave-like pain. Because the ureter shares nerve pathways with the groin and genitals, the pain often spreads there. Stones are more likely in people who do not drink enough fluid, and some medical conditions and diets raise the risk.

The warning signs that change the plan

Most renal colic, though agonising, is not immediately dangerous. But certain features turn it into an emergency. A high temperature, shivering or feeling very unwell alongside the pain suggests infection sitting behind a blocked kidney, which can become life-threatening quickly and needs urgent hospital treatment. Being unable to keep fluids down because of vomiting, pain that will not settle with treatment, or producing very little urine are also concerning. In someone with only one working kidney, or in pregnancy, a blockage is treated with extra urgency. In our illustrative case, if the person developed a fever and shakes, that would prompt immediate assessment rather than watchful waiting at home.

How doctors assess and investigate

Assessment starts with the story and an examination, checking temperature, pulse and blood pressure and feeling the tummy. A urine test looks for blood, which is common with stones, and for signs of infection. Blood tests check how the kidneys are working and look for infection. The key test to confirm a stone is usually a low-dose CT scan of the urinary tract, which shows the stone's size and position; in pregnancy an ultrasound is used instead to avoid radiation. Pain relief is given early and is a priority, because the pain is severe. Knowing the stone's size matters, as small stones usually pass on their own while larger ones may need a procedure.

Treatment, passing a stone and prevention

Many small stones pass by themselves over days to weeks, helped by good pain relief and plenty of fluids, and people may be sent home to let this happen with advice on what to watch for. Larger stones, or those causing a blocked, infected kidney, may need a hospital procedure to break up or remove the stone, or to drain the kidney urgently. Once the episode settles, attention turns to prevention, as stones often recur. Drinking enough fluid to keep urine pale, and dietary advice tailored to the stone type, both help. The core message of this case is that renal colic is usually not dangerous in itself, but fever with the pain is an emergency.