請點擊此轉換成中文
By Robin Cheng, MD, Urology and Urologic Surgery
Dr. Robin Cheng is a urologist at El Camino Health specializing in kidney stones and other urologic conditions. He grew up in the South Bay Area and attended Monta Vista High School in Cupertino, while also volunteering with the El Camino Health Auxiliary. Dr. Cheng earned a Bachelor of Science in biology at Stanford University, followed by his MD at Stanford University School of Medicine. He has completed his residency in urological surgery. He is fluent in both Mandarin Chinese and English, and is passionate about promoting urologic health education in the community.
Definition of Kidney Stone
Causes
Symptoms
Diagnosis
Treatment
When to see a doctor urgently
Prevention
Myths vs. facts
Frequently Asked Questions
What Are Kidney Stones?
Kidney stones are hard deposits made of minerals and salts that form in the kidneys from substances in the urine. They are relatively common, affecting about 1 in 10 people at some point in their lives.
The size of kidney stones can vary widely, ranging from as small as a grain of sand to as large as a golf ball. They may form when urine becomes overly concentrated, allowing crystals to develop and stick together.
Why Do Stones Form?
- Insufficient water intake: Not drinking enough water leads to concentrated urine, which increases the likelihood of crystal and stone formation.
- High intake of salt or animal protein: Excess salt can raise urinary calcium, and high animal protein intake can increase calcium and uric acid levels, both contributing to stone formation.
- Genetic factors: A family history of kidney stones significantly increases the risk of developing them.
- Certain medical conditions: Conditions like gout, inflammatory bowel disease (IBD), diabetes, obesity, hyperparathyroidism, and recurrent urinary tract infections can raise the risk of stone formation.
Common Symptoms:
- Severe flank pain (radiates to groin)
- Blood in urine (pink/red/brown)
- Nausea & vomiting
- Urgency or frequent urination
If a kidney stone remains in the kidney without obstructing the ureter, or if the stone is located in the bladder, it usually does not cause pain. However, if a kidney stone enters or blocks the ureter and prevents urine from draining, it can lead to hydronephrosis (kidney swelling), which in turn causes severe flank pain.
Some kidney stones are asymptomatic (known as “silent stones”) and are often discovered incidentally during CT scans.
How Are Kidney Stones Diagnosed?
- CT scan: The most accurate imaging test. It clearly shows the size, number, and location of kidney stones.
- Ultrasound: A safe and non-invasive test. It’s ideal for detecting hydronephrosis and some stones but may not visualize all stones clearly.
- X-rays: Can detect only certain types of stones, such as calcium-containing stones.
Reasons for Emergent Intervention
Hydronephrosis with the following conditions:
- Infection (which can lead to sepsis)
- Kidney injury
- Intractable pain
- Uncontrolled nausea and vomiting
If a stone blocks the ureter and leads to a urinary tract infection, urgent placement of a double-J ureteral stent or a nephrostomy tube is necessary to drain the urine and prevent the infection from spreading to the bloodstream.
Treatment Options:
Small stones (< 5 mm):
- Increase fluid intake to maintain a daily urine output of more than 2.5 liters
- Pain management
- Tamsulosin (Flomax) can be prescribed to facilitate stone passage
Larger stones:
- Extracorporeal shock wave lithotripsy (ESWL): Non-invasive; uses sound waves to break the stone into smaller pieces. Has a lower stone clearance rate compared to other procedures.
- Ureteroscopy with laser lithotripsy: Minimally invasive and commonly used. A thin scope is passed through the urethra to reach the stone, which is then fragmented with a laser. Usually performed as an outpatient procedure.
- Percutaneous nephrolithotomy (PCNL): Best suited for large or complex stones. Involves a small incision in the back to access and remove the stone. Requires general anesthesia and may involve a short hospital stay.
When to See a Doctor Urgently
- Severe and persistent flank pain
- Fever, chills (indicating infection)
- Inability to urinate (suspect bilateral obstruction or unilateral obstruction in someone with a solitary kidney)
- Severe nausea, vomiting, inability to eat or drink
How to Prevent Kidney Stones:
- Stay well-hydrated, aiming for a urine output of over 2.5 liters per day
- Drink lemon water (increases urinary citrate, which inhibits stone formation)
- Limit sodium intake to less than 2,300 mg per day
- Moderate animal protein intake (limit animal protein to no more than 0.8-1.0 grams/kg of body weight per day)
- Maintain normal calcium intake (1,000–1,200 mg daily, preferably from food)
- Limit high-oxalate foods (such as spinach, nuts, and chocolate)
- Maintain healthy weight and exercise regularly
- Eat a balanced diet, avoid extreme dietary practices
Key point: Staying well-hydrated is the single most important factor in preventing kidney stones.
Myths vs. Facts:
- Does calcium intake cause kidney stones?
A low-calcium diet may actually increase the risk of calcium oxalate kidney stones. When there isn't enough calcium in the intestines, oxalate cannot bind with calcium to form insoluble calcium oxalate that is excreted in the stool. As a result, more free oxalate is absorbed into the bloodstream and excreted by the kidneys, increasing urinary oxalate levels and promoting the formation of calcium oxalate stones.
Therefore, the key is to maintain a normal calcium intake, avoiding both excessive and insufficient amounts. Adults should aim for approximately 1,000 to 1,200 mg of calcium per day, preferably from dietary sources such as dairy products, small fish with bones, low-oxalate dark leafy greens, or calcium-fortified foods. - Do only men get kidney stones? Historically, kidney stones were more common in men, but over the past few decades, the incidence in women has been steadily increasing, making the male-to-female ratio more balanced — particularly among younger individuals.
- Does kidney stone treatment always require surgery?
Most small kidney stones can pass naturally and do not necessarily require surgery. However, if a stone is large, or if it causes obstruction, infection, or recurrent symptoms, minimally invasive surgical removal may be necessary.
Frequently Asked Questions:
- Q: An ultrasound only shows mild hydronephrosis, but no visible stones. What should I do?
A: A CT scan is recommended. Ultrasound often cannot clearly detect stones. However, if hydronephrosis is present, further evaluation is needed to rule out ureteral obstruction from a stone. - Q: How can I differentiate kidney stone pain from general back pain?
A: Kidney stone pain is usually sudden and intense, often in the side or flank. It may radiate to the lower abdomen or groin, accompanied by nausea, vomiting, or blood in the urine. In contrast, muscle or spine-related back pain is usually dull, related to posture or activity, and typically located more toward the center of the back. - Q: How can I differentiate blood in urine due to kidney stones from kidney cancer?
A: A CT scan with contrast is necessary to distinguish between kidney stones and tumors. - Q: Can hyperparathyroidism cause kidney stones?br>A: Yes. Hyperparathyroidism increases blood calcium levels, which raises urinary calcium and increases the risk of calcium stones. These patients usually need further evaluation by an endocrinologist. If diagnosed with primary hyperparathyroidism and symptoms or complications are present, surgery may be needed to remove the overactive parathyroid gland.
- Q: How do I know what type of stone I have?
A: If a stone is passed or surgically removed, it can be sent for stone composition analysis — the only definitive way to determine the stone type. If no stone is available, blood and 24-hour urine tests can help identify metabolic risk factors and suggest which types of stones you may be more likely to form, but they cannot determine the exact stone composition. - Q: Are kidney stones related to sodium intake?
A: Yes. Excess dietary salt (sodium) increases urinary sodium and calcium, raising the risk of calcium oxalate stones. It’s recommended to limit sodium intake to below 2,300 mg per day to help prevent stones. - Q: How can I know if I have hydronephrosis?
A: Hydronephrosis may cause flank pain, nausea, or vomiting but can also be asymptomatic. Ultrasound or CT scans are the most accurate tests for detecting hydronephrosis due to urine blockage. - Q: If a 1.5–2 cm kidney stone has no symptoms, can it be left untreated?
A: If the stone is causing hydronephrosis, infection, or impaired kidney function, treatment is generally recommended to prevent worsening.
If there are no symptoms and no signs of hydronephrosis, infection, or kidney injury, this type of larger kidney stone may be closely monitored after evaluation by a urologist.
However, the stone may still lead to future obstruction, pain, infection, or further decline in kidney function — and some stones may grow over time. Preventive treatment should be discussed with your urologist. - Q: What if I have an 8 mm kidney stone that has been present for 25 years without causing pain? Should I treat it?
A: If the stone is located in the kidney and hasn’t caused hydronephrosis, infection, or other symptoms, continued observation may be appropriate. Immediate treatment isn’t always necessary.
However, regular imaging (such as an ultrasound every 1–2 years) is recommended to monitor for any changes in size or position. If the stone is near the renal pelvis or ureteropelvic junction, you should discuss preventive treatment with your urologist to avoid sudden migration of the stone into the ureter, which could cause severe pain or obstruction. - Q: Can a kidney stone cause kidney damage over time?
A: If the stone doesn’t cause ureteral obstruction, hydronephrosis, or infection, it usually won’t harm the kidney immediately. However, stones that persist long-term can lead to chronic inflammation, recurrent infections, or gradual enlargement, which may eventually harm kidney function. Regular imaging follow-up is advised, and you should discuss with your urologist whether treatment is needed.
