Kidney stones: What causes them, what are the symptoms and who is most at risk?

Kidney stones are more common than you might think - about one in 10 people will get them. Photo / Getty Images

People who have had kidney stones have described it as the worst type of pain you can experience.

It’s more common than you might think - about one in 10 people will get kidney stones in their lifetime.

Kiwi golfer href="https://www.nzherald.co.nz/sport/golf/the-players-championship-ryan-fox-withdraws-due-to-illness-collin-morikawa-out-with-injury/4KTG6TDWBJCCRCTIZVY7ZCOMMI/" target="_self" rel="" title="https://www.nzherald.co.nz/sport/golf/the-players-championship-ryan-fox-withdraws-due-to-illness-collin-morikawa-out-with-injury/4KTG6TDWBJCCRCTIZVY7ZCOMMI/">Ryan Fox withdrew from The Players Championship in Florida last week, revealing kidney stones “took me down”.

Skipping the tournament to undergo surgery, Fox, 39, wrote on Instagram: “Devastated to miss out on such an amazing event, hoping to have a quick recovery and be back at it soon”.

Kidney stones are solid crystals that form in your kidneys from waste products in your urine, and can cause intense pain as they pass into your bladder.

But what exactly causes them to form - and what are the signs and symptoms to be aware of?

Kiwi golfer Ryan Fox had to withdraw from the Players Championship in Florida last week due to kidney stones. Photo / Getty Images

What causes kidney stones?

Dr Nadya York, an Auckland-based urologist and deputy leader of the Urological Society of Australia and New Zealand (USANZ) Endourology Special Advisory Group, says the main risk factor is low fluid intake.

“Your kidneys’ job is to excrete waste products, so there will always be various minerals in the urine,” she says.

“But if the urine is dilute, then they can never form a stone because they just get flushed out.”

If you get dehydrated playing sports, working in a hot climate or outside during summer without sufficient fluid intake, you’re at a higher risk of getting kidney stones.

“We see more stones in summer than we do in winter.”

Are there foods that can increase your risk?

If you’re prone to kidney stones, some foods could increase your risk of certain types forming, as they are known to change the composition of your urine.

Included are foods high in the compound oxalate - which is found in some plants, such as rhubarb, spinach, almonds and beans.

Foods high in sodium, such as processed foods and takeaways, can also increase the risk, as can eating too much animal protein.

Are there foods that can lower your risk?

Eating calcium-rich foods like dairy can help protect your kidneys, as calcium stops oxalates being absorbed into the blood and passed into the urine.

Eating plenty of fruit and vegetables can also lower your risk, along with staying hydrated.

What are the signs and symptoms?

Most kidney stones pass by themselves - it’s only when they create a blockage that they cause severe pain, York says.

“When it decides to move and pass through that really narrow tube called the ureter, which is the size and length of a spaghetti noodle, it causes urine backup - and it’s the urine backup that causes the pain.

“Once that blockage is relieved, then the pain goes away.”

The pain is typically felt from the back of the abdomen toward the front, lower abdomen.

“It can be quite severe; the patients are usually restless with pain and they might vomit if the pain is severe.”

Another symptom is blood in urine, though this doesn’t always occur, so people should see a doctor if they experience this type of pain, whether or not they also have blood in their urine.

Kidney stones can cause severe abdominal pain. Photo / 123RF

Who is most at risk of kidney stones?

You may have heard that men get kidney stones more often than women - but that’s not necessarily the case these days, York says.

“Traditionally, it’s been slightly more likely in men, but it’s now becoming more even.”

The risk increases with age, and kidney stones in younger people could point to a separate health issue.

“If they do get kidney stones starting in a younger age group, then we pay particular attention to prevention, because they’re more likely to have an underlying problem with calcium excretion or something else.”

If left untreated, stones can damage kidney function and even cause permanent impairment and failure.

What is the treatment?

Kidney stones less than 5mm are likely to pass by themselves, York says.

“As long as pain is under control and there is no infection, we would give people a bit of time to try and pass them, and they often do.

“Once the stone comes into the bladder, it’ll come out no problem, because the urine flow out of the bladder is much wider than the ureter.”

If a stone doesn’t pass by itself, an operation may be required - but these days, it isn’t major surgery like it might have been a few decades ago.

“We now have lots of minimally invasive treatments, whether it’s laser or shock wave, so you don’t need a major operation like you would have 20 years ago, 40 years ago,” York says.

“It takes one hour or so, we use laser or shock wave, and they usually go home the same day. In general, it’s now minimally invasive surgery, so we’re not making big cuts.

“For those really big ones, we go through the back, so we make a 1cm cut in the back ... but that’s relatively rare.”

If you’ve previously had kidney stones, drinking plenty of fluids can help prevent new ones - York recommends around 2.5 to 3 litres a day.

“For prevention, the number one thing ... is to get the fluid right.”

Bethany Reitsma is a lifestyle writer who has been with the NZ Herald since 2019. She specialises in all things health and wellbeing and is passionate about telling Kiwis’ real-life stories.