Kidney Stones

Overview

A kidney stone is a small, hard lump that forms when dissolved minerals in the urine become so concentrated that they crystallize and clump together. Many stones are tiny and pass unnoticed. The trouble — and the famously severe pain — begins when a stone large enough to get stuck travels out of the kidney and into the ureter, the thin muscular tube that carries urine to the bladder.

How the system normally works

Each kidney filters waste from the blood and produces urine, which collects in a funnel-shaped space (the renal pelvis) and drains down the ureter into the bladder. The ureter is only a few millimetres wide and pushes urine along with gentle squeezing waves. Because it is so narrow, even a small stone can plug it completely.

What goes wrong

When the urine is too concentrated — from not drinking enough, or from too much calcium, oxalate or uric acid — crystals form and grow into a stone. If that stone enters the ureter and lodges, urine can no longer drain. It backs up, stretching the ureter and the kidney behind it (a state called hydronephrosis). The ureter also squeezes hard in spasms trying to push the stone along. This stretching and spasm is what produces the intense, colicky pain.

Symptoms and why they happen

• Severe waves of flank pain that may radiate to the groin — from the stretched, spasming ureter as the stone moves.
• Restlessness — unlike many belly pains, people often can't lie still and pace or writhe.
• Blood in the urine (pink, red or brown) — the stone scrapes the delicate lining.
• Nausea and vomiting — the kidney and gut share nerve pathways.
• Frequent, urgent urination — especially as a stone nears the bladder.

Causes and risk factors

• Low fluid intake / dehydration (the biggest factor)
• Diets high in salt, animal protein, or oxalate-rich foods
• Obesity, diabetes, and gout
• Family history of stones
• Certain medical conditions and medications

How it's diagnosed

A CT scan of the abdomen without contrast is the most accurate test and shows the stone's size and exact position; ultrasound is often used first, especially in pregnancy or to avoid radiation. Urine tests look for blood and infection, and blood tests check kidney function. The stone's size matters: small ones (under ~5 mm) usually pass on their own; larger ones often need help.

Treatment and management

For a passing stone, the mainstays are pain relief, fluids, and time, sometimes with a medication that relaxes the ureter to ease the stone out. Stones that are too large, won't pass, or cause infection or blockage may be treated with shock-wave lithotripsy (breaking the stone with focused sound waves), ureteroscopy (a thin scope passed up to remove or laser the stone), or rarely keyhole surgery. A temporary stent may be placed to keep the ureter open.

Possible complications

A stone that fully blocks the kidney can damage it over time. The most dangerous combination is a blocked kidney plus infection, which can lead to a rapidly spreading, life-threatening infection requiring urgent drainage.

Prevention and outlook

Most people recover fully, but stones commonly recur. The single best prevention is drinking enough water to keep urine pale, alongside reducing salt, moderating animal protein, and following any diet tailored to the stone's mineral type. With good fluid habits, recurrence can be cut substantially.