Kidney Stones

Kidney stones form when urine contains high concentrations of substances capable of producing crystals, such as calcium, oxalate or uric acid. Normally, urine also contains substances that help prevent these crystals from sticking together. When the balance changes — particularly when there is too little fluid to dilute the urine — crystals can form, gradually combine and develop into a stone. Calcium-containing stones are the most common, but uric acid, struvite and cystine stones can also occur, each with different underlying risk factors.

Dehydration is an important risk factor because producing smaller amounts of concentrated urine makes crystallisation more likely. Diet can also influence stone formation in susceptible people, particularly high salt intake and, for certain stone types, excessive amounts of particular animal proteins or other dietary components. Family history, obesity, digestive conditions that alter nutrient absorption and metabolic disorders can increase risk. Certain medications and supplements may also contribute. Some people have abnormalities affecting calcium, uric acid or other substances in the urine, while rarer inherited conditions such as cystinuria can cause recurrent stones.

A stone may remain inside the kidney without causing symptoms. Problems often begin when it moves into the ureter, the narrow tube carrying urine from the kidney to the bladder. A stone obstructing this tube can cause renal colic — typically severe pain in the side or back that may travel towards the lower abdomen or groin and often comes in waves. Nausea, vomiting, urinary urgency and blood in the urine can occur. Obstruction becomes particularly concerning when it occurs alongside a urinary infection because infected urine may become trapped above the blockage, potentially leading to a serious kidney infection or sepsis.