Kidney stones: the need-to-know guide

Kidney stones, also called renal calculi or nephroliths, are formed when excess minerals and salts in the body build up and become crystalline hard deposits. They can be caused by not drinking enough water and other fluids, or because of certain medical conditions that cause an aggregation of these substances in urine. Miss Jean McDonald, a celebrated urologist, shares the causes of the phenomenon and the available options for treatment.

Despite their name, kidney stones also can be found in the urinary tract, ranging in size from a grain of sand to a golf ball -- although it is rare. A smaller one can pass through the body in the urine without notice it was ever there, but a larger one can cause significant obstruction, which will lead to complications such as preventing urination, necessitating its removal.

What causes kidney stones?

Kidney stones are caused when the urine contains more crystal-forming substances than fluid to dilute them. This includes minerals such as calcium, oxalate, and uric acid. Without enough fluid, these minerals start to clump together over months or even years, and eventually form into stones.

There are four kinds of kidney stones:

• Calcium stones, which make up the majority of kidney stones (as a calcium oxalate compound). The liver naturally makes oxalate, but we also absorb more from the food we eat. Some metabolic conditions, insufficient fluid intake, and high doses of vitamin D can increase the levels of calcium and oxalate in the urine.
• Uric acid stones, which can be caused by eating too much meat and eggs.
• Struvite stones, which are caused by the body responding to a urinary tract infection. These stones can grow quite large.
• Cystine stones, which form only in those who have a genetic disorder called cystinuria that causes the kidneys to excrete too much cysteine (a kind of amino acid).

The risk for forming kidney stones is higher for those who have obesity or diabetes, have diets that are high in sodium, meat and sugar, or are dehydrated due to not drinking enough or living in dry, hot environments.

What do kidney stones feel like?

Kidney stones will have no outward symptoms or cause sensation until they move around the body, either within the kidney or passing into one of the ureters (the tubes that connect the kidneys to the bladder), which can cause a significant amount of pain:

• That is sharp and intense in the sides and the back below the ribs
• That radiates to the lower abdomen and groin
• That comes in waves
• That feels like burning when urinating

This is because a stone can get stuck in the ureters, obstructing the flow of urine which will make the kidney swell and spasm. Other possible symptoms are blood in the urine, foul-smelling urine, cloudy urine, more frequent urge to urinate, nausea or vomiting, and fever in the case of infection.

Blockages that aren’t addressed with treatment or resolved naturally by the stone passing on its own can progress to kidney infection (pyelonephritis), frequent UTIs, acute kidney failure, and chronic kidney disease.

To diagnose kidney stones, doctors typically will test the urine for blood, infection, or to get a reading on its chemical composition. They may need to do further tests such as imaging scans (like X-rays, CT, or ultrasounds) to check on your kidneys and urinary tract as well as the size and amount of the stones, or a blood test to see if the levels of minerals like calcium are too high.

How are kidney stones treated?

Kidney stones that are small enough are likely to pass through without too much discomfort, though it is recommended that the patient keeps an eye on their symptoms. Small stones around 4mm wide can pass within a week or two, whereas one that is a little larger could take a month to pass. Patients may be prescribed medications to help with pain and facilitate the passing of the stone. These include medicines to relax the ureters such as tamsulosin and nifedipine.

For larger stones that cannot pass or stones that are causing severe pain, surgery will likely be needed. There are a few procedures that can be done to achieve this, and which is performed will depend on the size and location of the stone:

• Shockwave lithotripsy (SWL), in which ultrasonic shockwaves are used to break down the stone into smaller pieces so they can be passed naturally. It can take around 40 minutes to perform, and this can be an unpleasant experience which is why patients are offered an anaesthetic beforehand.
• Ureteroscopy, in which a cystoscope with instruments is inserted through the urethra and bladder and into a ureter to manually break up and remove the stone.
• Percutaneous nephrolithotomy, in which a tube is inserted into the kidney directly through a cut in the back and an ultrasonic probe breaks up the stone into smaller pieces.
• Laparoscopic surgery, which is used in cases where other procedures are not possible. A small incision is made through which surgeons can manually remove the stone, visually guided with the laparoscope.

Very rarely, the removal of a kidney stone will not be possible with the above technique and surgeons will need to perform an open surgical procedure instead.

Can kidney stones be prevented?

To prevent kidney stones, it is recommended to drink a lot of water (urine, ideally, should be a pale, translucent yellow or green). Avoid excessively consuming animal proteins, foods that are high in sugar,  sodium and oxalates (such as peanuts and rhubarb).

If you are currently struggling with urinary or prostatic issues, Miss Jean McDonald is an experienced urologist in London and Essex and is available for consultation via her Top Doctors profile.