What Are Kidney Stones and How Do They Form

Kidney stones are hard deposits that build up inside your kidneys over time. They form when certain substances in your urine become too concentrated and crystallize. Your kidneys filter waste from your blood to create urine, but sometimes minerals and salts stick together instead of staying dissolved. These clumps gradually grow larger, eventually creating a stone-like object that can range from the size of a grain of sand to the size of a golf ball.

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The most common type of kidney stone contains calcium oxalate. Other types include uric acid stones, struvite stones (which form from urinary tract infections), and cystine stones (a rare hereditary condition). Most kidney stones form because of dehydration. When you don't drink enough water, your urine becomes more concentrated, making it easier for minerals to crystallize and form stones.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, about 1 in 11 people in the United States will develop a kidney stone at some point in their life. Men are more likely to develop them than women, with men accounting for about 70% of cases. The risk increases with age, with most cases occurring between ages 30 and 50.

Several factors increase your risk of developing kidney stones, including family history (if your parents had stones, you're more likely to develop them too), previous kidney stones (people who've had one are likely to develop another), certain medical conditions like gout or high blood pressure, and specific medications. Diet also plays a role—eating foods high in sodium, animal protein, or oxalate can contribute to stone formation.

Practical Takeaway: Understanding that kidney stones form from concentrated minerals helps explain why staying hydrated is so important for prevention. If you have risk factors like family history or have had stones before, drinking adequate water daily is one of the most important steps you can take.

Recognizing the Symptoms of Kidney Stones

Kidney stone symptoms can vary greatly depending on the size and location of the stone. Small stones that don't block urine flow may cause no symptoms at all and pass unnoticed. However, larger stones or those that block the flow of urine typically cause noticeable pain and other symptoms. The most common symptom is sudden, severe pain that starts in the side or back, below the ribs. This pain often comes in waves and may move to the lower abdomen or groin as the stone travels through the urinary tract.

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The pain associated with kidney stones is often described as one of the worst pains people experience and is sometimes compared to childbirth. A single kidney stone can cause pain for different periods—some stones cause pain for just a few minutes while others cause pain for hours or even days. The pain typically doesn't respond well to over-the-counter pain medication, which is one reason people often seek emergency care.

Besides severe pain, other symptoms of kidney stones include:

  • Blood in the urine (which may look pink, red, or brown)
  • Nausea and vomiting
  • Persistent need to urinate
  • Urinating more often than usual
  • Burning sensation during urination
  • Fever (which may indicate a urinary tract infection)
  • Chills

It's important to note that not everyone experiences the same symptoms. Some people may have blood in their urine without pain, while others may have severe pain without any visible blood. Women sometimes confuse kidney stone pain with gynecological issues, while men might mistake it for prostate problems. The key distinguishing feature of kidney stone pain is that it typically comes in waves and is extremely severe.

Practical Takeaway: If you experience sudden severe pain in your side, back, or lower abdomen—especially if accompanied by blood in urine, nausea, or frequent urination—these may be signs of a kidney stone. Keep track of when symptoms started, what they feel like, and what makes them better or worse, as this information helps healthcare providers.

Understanding When to Seek Medical Care

Deciding when to seek care for a suspected kidney stone depends on the severity of your symptoms and other health factors. Not every kidney stone requires emergency treatment, but certain situations warrant medical attention sooner rather than later. Understanding the difference between situations that need emergency care and those that can be managed with a regular doctor's visit helps you make the right choice.

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You should seek emergency care (by going to an emergency room or calling 911) if you experience:

  • Severe pain that you cannot manage or that is incapacitating
  • Pain accompanied by fever and chills (suggesting infection)
  • Pain accompanied by vomiting and inability to keep down fluids or medications
  • Blood in urine along with pain
  • Pain in only one kidney and having only one kidney (or previous kidney removal)
  • Symptoms of urinary tract infection along with kidney stone symptoms
  • Inability to urinate at all

You should contact your regular healthcare provider (and may be able to schedule an appointment rather than going to the emergency room) if you have mild to moderate pain without fever, can keep down fluids and food, have no signs of infection, and have two functioning kidneys. Your provider can order imaging tests to confirm whether you have a kidney stone and discuss treatment options.

A kidney stone complicated by infection is a medical emergency because the combination can quickly lead to serious complications like sepsis (a life-threatening response to infection). That's why fever and chills along with kidney stone symptoms always warrant emergency care. Similarly, if you have only one kidney or have had one kidney removed, even an uncomplicated stone needs prompt evaluation because you cannot afford to lose kidney function.

Practical Takeaway: The presence of fever, infection symptoms, inability to urinate, or severe vomiting transforms a kidney stone from something you might manage with pain control into a medical emergency. If you're unsure whether your symptoms warrant emergency care, calling a nurse hotline or your doctor's office for guidance can help you decide appropriately.

Medical Evaluation and Diagnosis of Kidney Stones

When you seek medical care for a suspected kidney stone, healthcare providers use several methods to confirm the diagnosis and determine the best treatment approach. The process typically begins with a physical examination and questions about your symptoms. The doctor will ask when the pain started, how severe it is, whether you've had kidney stones before, and whether you have any medical conditions or take medications that might affect kidney stone formation.

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After the initial evaluation, providers usually order imaging tests to confirm the presence of a kidney stone and determine its size and location. A CT scan (computed tomography scan) is considered the gold standard for kidney stone diagnosis because it can detect even very small stones and can show whether the stone is blocking urine flow. A CT scan without contrast dye is often used because it provides clear images of stones without requiring an injection. Plain X-rays may also be used to visualize larger stones containing calcium.

Ultrasound is another imaging option that is sometimes used, particularly in pregnant patients or those who need to avoid radiation. An ultrasound uses sound waves to create images and carries no radiation risk. Urine tests may also be ordered to check for blood in the urine and to look for signs of urinary tract infection.

Once a kidney stone is confirmed, your healthcare provider needs to know its size, location, and composition to determine treatment. Small stones (less than 5 millimeters) often pass on their own with conservative treatment. Stones between 5 and 10 millimeters pass spontaneously about 50% of the time. Stones larger than 10 millimeters rarely pass on their own and usually require intervention. Stones lodged in certain locations, such as where the ureter meets the bladder, are less likely to pass than stones in other locations.

If you've passed a kidney stone or had one surgically removed, your provider may recommend having it analyzed to determine its composition. Understanding what type of stone you had helps guide prevention strategies. For example, if you had a calcium oxalate stone, dietary changes and increased water intake take on different importance than if you had a uric acid stone.

Practical Takeaway: During your medical evaluation, be prepared to describe your