Kidney stones, also known as nephrolithiasis or renal stone disease, occur when the urine contains an excess of minerals, usually calcium. This leads to the accumulation of minute crystals, which form solid masses over time.

The composition of kidney stones can vary according to which excess minerals are present in the urine. The most common kidney stones contain calcium. In some cases, stones form when calcium combines with other chemicals; examples are calcium oxalate and calcium phosphate stones. Other stones may be formed from struvite, uric acid or cystine, but these occur less frequently.
Kidney stones can stay within the kidney or they can pass into the ureter and on to the bladder. Small stones can sometimes be passed in the urine without causing much pain but larger stones can get stuck in the urinary tract. This can happen in the ureter, in the bladder, or in the urethra and often causes intense pain as well as blocking the flow of urine.

Who gets kidney stones?

More men than women develop kidney stones and the condition usually affects people between the ages of 30 and 60 years, especially those with a family history.

Dehydration is a major risk factor for kidney stones.  This is because as the blood and, subsequently, the urine become depleted of water content, the relative concentrations of minerals become greater. Other causes include:

  • Medication such as certain HIV treatments and diuretics.
  • An overdose of vitamins, minerals or antacids.
  • Too much protein in the diet.
  • Having a kidney that is scarred, has cysts, or is of abnormal shape.

People who have had recurrent urinary tract infections may be more susceptible to developing struvite stones, while people with gout or those receiving chemotherapy can sometimes produce kidney stones composed of uric acid. Rarely, cystine stones can occur, caused by a disorder called cystinuria. This runs in families and causes a defect in the ability of the kidneys to reabsorb cystine, causing it to build up in the urine and form kidney stones.

What are the symptoms of kidney stones?

The most characteristic symptom of kidney stones is severe pain or aching in your back. This is renal colic and it occurs as soon as kidney stones start moving or become stuck in the urinary tract.

Renal colic tends to occur in waves or spasms and can affect one or both sides of your back, eventually radiating round to your abdomen and possibly reaching your groin and genitals. You may also notice that you need to urinate more often, feel a burning sensation when you do urinate, and that your urine is cloudy or contains blood. Kidney stones can sometimes cause nausea, vomiting and feverishness. 

If stones cause a blockage within your kidney, you may experience kidney damage or infection. It is therefore important to seek urgent medical attention if you experience the above symptoms.