Kidney stones: finding the cause and preventing them
Kidney stones are common, and after one stone another becomes more likely. This page explains how stones form and what they are made of, what finding the cause and prevention involve, and where the work of the urologist and the nephrologist divides.
What is a kidney stone?
NIDDK describes kidney stones as hard, pebble-like pieces that form in the kidney when the urine contains a lot of certain minerals. They range in size from a grain of sand to about a pea, and rarely much larger. Small stones often pass out in the urine without notice, but a larger stone may block the urinary tract and cause severe pain or bleeding.
Types of stone (NIDDK):
- Calcium stones (calcium oxalate and calcium phosphate), which are the most common.
- Uric acid. When the urine is too acidic.
- Struvite. Sometimes after a urinary infection, and it can grow quickly.
- Cystine. Linked to a rare inherited condition called cystinuria.
NIDDK says the risk is higher with: being male, a family history, an earlier stone, drinking too little fluid, a blocked urinary tract, repeated urinary infections, gout, obesity, bowel disease and long-term use of some medicines. NIDDK names water tablets and calcium-based antacids, but some water tablets are prescribed to prevent calcium stones (NKF). If you take one of these, do not stop it yourself; talk to your doctor.
Symptoms
Sharp pain in the side, back, lower abdomen or groin that is constant or comes and goes; pink, red or brown urine; frequent or burning urination; cloudy or foul-smelling urine; nausea and vomiting; fever and chills (NIDDK). NHS says the pain may come in waves, with varying intensity.
Who should be seen?
- Someone with pain that might be a stone, or blood in the urine, for the first time.
- Someone who has passed or had a stone treated and wants to stop it coming back.
- Someone who has had several stones. NKF says these people should have a 24-hour urine test at least once a year. This advice is for follow-up, and the doctor decides.
- Someone with an underlying condition such as gout or a problem with the parathyroid glands.
How is it assessed?
NHS writes that the doctor usually diagnoses from the symptoms, history, medicines, diet and family history. Urine or blood tests and sometimes imaging (for adults usually a CT scan in hospital) are used too. The remaining steps are for finding the cause:
- If a stone is passed, NIDDK says you may be asked to keep it for testing so its type can be known.
- A 24-hour urine test measures the amount of urine and its minerals (NIDDK).
- Blood tests for things such as calcium and uric acid, and a check for underlying conditions.
The type of stone and the results of these tests decide which change in diet or medicine helps.
What does treatment look like overall?
Passing the stone. NHS says most stones are treated at home with medicines and extra fluids (unless your doctor has limited your fluids), and passing may take several weeks. Medicine is prescribed for pain, for nausea and to help the stone pass.
Removing the stone. A stone too large to pass needs treatment. A stone that has blocked the urine or comes with infection needs urgent treatment. The methods (NIDDK) are:
- Shock wave lithotripsy from outside the body.
- Ureteroscopy: a thin tube goes up through the urinary tract and the stone is removed or broken up.
- Percutaneous nephrolithotomy: for larger stones, through a small cut in the back.
NIDDK counts these methods as the work of the urologist.
Prevention. This is where the nephrologist usually has a role. NIDDK and NKF say prevention depends on the type of stone and a 24-hour urine test. For calcium stones, NKF names measures such as cutting down on salt and added sugar, getting enough calcium from food, limiting animal protein and avoiding dietary and herbal supplements. If your doctor prescribed a supplement or calcium, do not stop it yourself. Some patients are also given medicine: the choice depends on the type of stone and should be discussed with your doctor (NIDDK). If an overactive parathyroid gland is the cause, it needs treatment.
What you can do
- Drink enough fluid, mostly water. Settle the exact amount with your doctor. If you have kidney or heart failure, do not increase it on your own (NIDDK). The colour of urine is a simple guide.
- Cut down on salt. NIDDK says limiting salt is needed for calcium stones even if you take medicine.
- Do not cut out calcium from food. NIDDK says dietary calcium does not raise the risk of oxalate stones.
- Do not raise animal protein for no reason, but do not remove protein completely either. NIDDK writes this for some types of stone, and the amount should be set with a dietitian.
- Do not take “stone-dissolving” supplements or herbal teas without asking.
- Keep a passed stone for testing.
- Follow up underlying conditions such as gout, obesity and repeated urinary infections.
When to get urgent help
- Severe flank pain that cannot be borne, or pain with repeated nausea and vomiting.
- Fever or chills. NHS says a stone with symptoms and a high temperature or chills needs urgent attention.
- You are passing no urine or very little.
- A lot of blood or clots in the urine.
- Flank pain with fever and chills can also be a sign of kidney infection (NHS: Kidney infection).
- Stone pain in someone with one kidney, a transplant or chronic kidney disease.
In Iran, call 115, Iran’s emergency number, or go to the nearest emergency department. See the full list in the guide “When to get urgent help”.
Frequently asked questions
I had my stone treated. Why should I look for the cause?
NIDDK says having one stone raises the chance of another. NKF considers recurrence of stones common and says prevention depends on the type of stone and a 24-hour urine test. For this reason, once the stone is dealt with, finding the cause and the type of stone is part of treatment.
How much water should I drink to prevent stones?
Drinking enough water is the most important step in prevention (NIDDK), but the right amount depends on your situation. Different sources give different figures, and NIDDK says someone with kidney failure should ask their doctor about fluid limits. NHS says the colour of urine is a good guide and dark urine means dehydration. There is no fixed number for everyone.
Should I stop calcium?
Usually not. NIDDK says calcium in the diet does not make stones and, in a suitable amount, may stop stone-forming substances being absorbed in the gut. What may be limited is salt and animal protein, and for oxalate stones, foods high in oxalate. This advice depends on the type of your stone, so ask your doctor or dietitian.
Does a urologist or a nephrologist treat the stone?
NKF writes that the urologist monitors the stone or removes it by surgery, and may refer you to a nephrologist for more specialised prevention. So the work of the two specialities complements each other. See the article "Nephrologist or urologist?"
My stone became painful with fever and chills. Should I wait?
No. NHS says a stone with symptoms needs urgent help, and severe pain or a high temperature or chills needs urgent attention. A stone with infection can be dangerous. See the last section.