What are kidney stones?
Your kidneys are essential for filtering blood and removing excess fluids and waste products as urine. Occasionally, these waste products aggregate into hard crystals known as kidney stones (renal calculi). Kidney stones rank among the most common urinary tract disorders and can vary in size from a grain of sand to a golf ball. They can be extremely painful and may obstruct urine flow, leading to serious complications. Anyone can develop kidney stones, but they occur more often in men than in women. The lifetime risk is about one in ten for men and one in thirty-five for women. At any given time, roughly 4–8 % of Australians are affected.
Kidney stone symptoms
Stones often remain silent until they migrate into the ureters (the tubes that connect the kidneys and bladder). When a stone lodges there, it can block the flow of urine, producing symptoms. The hallmark sign is renal colic, an abrupt, severe pain typically felt in the flank below the ribs that may:
- be sharp, cramping, or gripping
- radiate to the lower abdomen and groin
- come in waves or fluctuate in intensity
- cause a burning sensation during urination
Other possible indications include:
- nausea or vomiting
- blood in the urine
- fever with chills
- cloudy or foul-smelling urine
- tiny, gravel-like particles in the urine
- a sudden, urgent need to urinate
- decreased urine output (complete stoppage is a medical emergency)
What causes kidney stones?
There is no single cause of kidney stones, but several risk factors contribute to their formation:
- inadequate fluid intake
- high concentrations of calcium, oxalate, cystine, or uric acid in the urine
- underlying health conditions such as urinary tract infections, digestive disorders, inflammatory bowel disease, hyperparathyroidism, sarcoidosis, certain cancers, gout, high blood pressure, or obesity
- certain medications (e.g. antivirals or treatments for kidney disease, cancer, or HIV)
- a diet high in salt
- a personal or family history of kidney stones
Types of kidney stones
There are four main varieties of kidney stones, and knowing which one you have can guide both treatment and prevention strategies: 1. Calcium stones These account for most cases and consist of calcium combined with oxalate or phosphate. 2. Struvite stones Often developing after a urinary tract infection, these stones can grow large and take on a horn-like shape. 3. Uric acid stones Common in people who lose excessive fluids (for example, due to chronic diarrhoea or malabsorption), those on high-protein diets, or individuals with diabetes or metabolic syndrome. 4. Cystine stones Rare and crystalline in appearance, these stones arise in people with a hereditary condition.
How are kidney stones diagnosed?
Stones sometimes surface incidentally during examinations for other health issues. If a stone is suspected, your doctor may order:
- Urine and/or blood tests
- Ultrasound imaging
- CT scans
- X-rays, including an intravenous pyelogram (IVP), where contrast dye is injected before imaging to highlight the kidneys, ureters, and bladder
If you happen to pass a stone, try to collect it and bring it to your doctor for analysis, this helps pinpoint the stone’s composition and tailor both treatment and prevention.
How are kidney stones treated?
Most stones will pass spontaneously within three to six weeks. During this period, it’s important to drink plenty of water to help flush them out. Pain relief medication may be needed, and severe pain could require hospital admission for stronger analgesics. If a stone is too large to pass, blocks urine flow, causes bleeding, or leads to infection, more active treatments may be recommended:
- Extracorporeal shock wave lithotripsy (ESWL) to break stones (<2 cm) into fragments that can be passed naturally
- Percutaneous nephrolithotomy, a minor surgical procedure involving a small incision in the back to remove stones
- Ureteroscopy, where a thin instrument (ureteroscope) is threaded through the urethra into the ureter; small stones may be extracted directly, while larger ones are fragmented and then removed.
Potential complications
Kidney stones can sometimes lead to serious issues such as acute kidney injury or chronic kidney disease, making prompt medical evaluation essential.
When to seek medical attention
If you notice any symptoms of kidney stones, contact your doctor. You should get immediate care if you experience any of the following:
- Intense pain that prevents you from sitting comfortably
- Pain accompanied by nausea and vomiting
- Pain with fever and chills
- Difficulty urinating
- Blood in your urine
Preventing kidney stones
You can reduce your risk of stone formation by adopting these lifestyle changes:
- Drinking plenty of water each day
- Limiting beverages high in phosphoric acid (e.g. cola and beer)
- Preventing and promptly treating urinary tract infections
- Cutting back on animal protein (red meat, poultry, eggs, seafood)
- Including fruit juices like cranberry, orange, or grapefruit
- Adding dairy products to your diet
- Reducing salt intake
- Checking with your doctor before taking calcium supplements
If you’ve had stones before, your physician may also prescribe medication alongside these measures to help prevent new ones. Treatment depends on stone type but can include:
- Calcium stones, drugs to increase urine flow
- Struvite stones, long-term antibiotics to stop UTIs
- Uric acid stones, medications to lower uric acid and alkalinize urine
- Cystine stones, agents that reduce cystine in the urine