Understanding kidney stones

What kidney stones are

The kidneys clean the blood and make urine, which carries away waste and extra water. Urine contains many dissolved substances, and if some of these become too concentrated they can crystallise and clump together, gradually building up into a hard stone. Stones can be as small as a grain of sand or as large as a pebble, and there are several types depending on what they are made of, the most common being those containing calcium. A stone may sit quietly in the kidney and cause no trouble at all. Problems usually begin when a stone moves and gets stuck in the narrow tube, called the ureter, that carries urine from the kidney to the bladder. This blockage stretches the system and triggers pain. Understanding this helps explain why symptoms often come on suddenly and in waves.

Why stones form

Stones form when urine becomes too concentrated, allowing minerals to crystallise. The single biggest factor is not drinking enough fluid, especially in hot weather or for people who sweat a lot, because concentrated urine makes crystals more likely. Diet plays a part too: very high salt intake, and for some people large amounts of certain foods, can raise the risk. Being overweight, some medical conditions affecting the way the body handles minerals, repeated urine infections, and certain medicines can all contribute. Family history matters, so stones can run in families. Once someone has had a stone, they are more likely to form another, which is why prevention becomes important after the first one. In many cases no single cause is found, but the common thread is urine that is too concentrated for too long, which is exactly what prevention aims to change.

Symptoms and warning signs

A stone sitting still in the kidney often causes no symptoms and may be found by chance. Trouble starts when a stone moves and blocks the flow of urine. This can cause a sudden, severe pain, usually in the side or back below the ribs, that may spread to the lower tummy and groin. The pain often comes in waves, can be extremely intense, and may make a person restless and unable to get comfortable, sometimes with nausea or vomiting. There may be blood in the urine, making it pink, red or brown, and a need to pass urine more often. This severe pain is known as renal colic. Warning signs that need urgent help include pain with a high temperature and shivering, being unable to pass urine, or feeling very unwell, as these can point to a serious infection or blockage.

How stones are treated

Treatment depends on the size and position of the stone. Many small stones pass out on their own in the urine over days or weeks, helped by drinking plenty of fluids and taking pain relief; sometimes a medicine is given to help the stone pass more easily. Doctors usually confirm the diagnosis with a scan and check the urine and blood. Larger stones, or those that will not pass or are causing a blockage or infection, need active treatment. Options include a technique that uses sound waves to break the stone into smaller pieces so it can pass, and procedures where a thin telescope is passed up to reach and remove or break the stone, avoiding open surgery in most cases. If infection and blockage occur together, this is urgent, and the blockage may need to be relieved quickly. Most people recover well after treatment.

Preventing future stones

Because stones often come back, prevention is worthwhile. The most important step by far is drinking enough fluid throughout the day so that urine stays pale rather than dark, which keeps minerals dilute and less likely to crystallise; more is needed in hot weather or with heavy exercise. Reducing salt in the diet helps, as does keeping to a healthy weight. Depending on the type of stone, a doctor or dietitian may give tailored advice about particular foods, and it is best to follow individual guidance rather than cutting out food groups unnecessarily. Anyone who has had a stone analysed can receive advice specific to its type. For people who keep forming stones, further tests and sometimes preventive medicines may be offered. Simple, consistent habits, especially good hydration, make a real difference in reducing the chance of another painful episode.