Introduction
Kidney stones (medical term: 'renal calculi') are very common and during their lifetime men in Australia have a 1 in 10 chance of having them at some point, with women having a 1 in 35 chance.
Kidney stones are in fact lumps of hard crystalline material that form on the inside surface of the kidney. There are different types of kidney stones, including:
- Calcium-based composition stones – the most common form of kidney stone, normally composed of calcium oxalate or calcium phosphate
- Uric acid composition stones – these can be caused by a high protein diet and can occur in patients who have gout
- Cystine composition stones – these are uncommon and are often hereditary
- Struvite composition stones – these contain magnesium and ammonia and are often related to urinary tract infection
After having a kidney stone there is a 30%-50% chance of developing another one within 5 years, although after the 5 year mark the likelihood of getting another goes down. Some people suffer from kidney stones for their entire lives.
Causes
Kidney stones form due to minerals and other substances in the urine reaching high concentrations and crystallising in the kidneys. As they crystallise, they can form hard lumps – stones – which can in turn cause pain, block urine flow and cause infection and even kidney failure.
Although most stones form due to high concentrations of specific substances, kidney stones can also form when these levels are normal. In general terms the following are regarded as risk factors for kidney stone formation:
- Age – kidney stones occur most frequently between 20-40 years of age
- Gender – men are up to three times as likely to develop kidney stones than women
- Dehydration
- Obstruction to drainage of urine
- Obesity
- Family history
- Recurrent urinary tract infections
- Gout
- Some medications – especially some diuretics and medications used to treat HIV and cancer
Symptoms
Kidney stones can be present with no symptoms at all. The first symptom of a kidney stone is usually pain – often an intense pain referred to as 'renal colic', caused by the stone moving through the urinary tract. The location of the pain is typically in the back below the ribs, but it can also spread to the front of the torso and to the groin. The intensity of this pain can lead to nausea and vomiting in some cases.
Other symptoms include:
- Haematuria – blood in the urine
- Fever – this can be a sign that the urine has become infected
- Urgent need to urinate
Tests / Diagnosis
There are a number of tests that can be performed to diagnose kidney stones. These are:
- Abdominal X-ray
- Non-contrast CT scan of the entire urinary tract
- Ultrasound of the urinary tract
- Intravenous pyelogram – this will identify obstruction of the urinary tract.
- Blood test – to test for presence and levels of stone-forming minerals in the body
- Analysis of stone after it has passed can help diagnose the underlying cause