What are Kidney Stones?
Kidney stones (nephrolithiasis) are salts or crystals that precipitate in the urinary tract. These stones are typically made up of elements such as calcium (most common), uric acid, magnesium ammonium phosphate, or cysteine. The urinary tract begins with the kidneys, which empty urine into the ureters, which then drain urine into the bladder and finally the urethra. Stones can be located anywhere along the urinary system from the kidneys to the bladder.
Patients with kidney stones typically develop acute onset of pain that starts in the flank region or back on one side. The pain tends to travel towards the groin and is often described as being colicky – this means that the pain comes and goes as the stone works its way down the ureter. Patients may have severe pain, often described as giving birth. Associated symptoms include urinating frequently and blood in the urine.
Severe cases of kidney stones can cause urinary obstruction and infection, which may require interventional procedures to remove them.
What Causes Kidney Stones?
Kidney stones are made up of various minerals that form crystals – these most often include:
- Calcium phosphate or calcium oxalate
- Uric acid
- Magnesium ammonium phosphate (struvite)
The cause of kidney stones depends on the type of stone that is implicated. Calcium stones are the most common and typically occur individuals with low urine volume, high urine calcium, high urine oxalate, and low urine citrate. This usually affects individuals who do not drink enough fluids and have underlying medical conditions such as primary hyperparathyroidism, obesity, gout, and diabetes.
Uric acid stones generally occur in patients with low urine volume, high urine concentration of uric acid, and acidic urine. They usually affect individuals with gout, chronic diarrhea, diabetes, or metabolic syndrome. Struvite stones occur in patients with kidney infection due to Proteus. Cysteine stones typically occur in children with a rare genetic disorder.
How common are Kidney Stones?
Kidney stones are common in the United States and are responsible for a relatively high number of emergency department and primary care clinic visits. Advanced cases often require consultation with a urology specialist – this is especially true if first-line measures are unsuccessful.
The condition is more commonly seen in adults. In the United States, patients between age 10-19 make up for only about 4% of cases. The incidence of nephrolithiasis in Americans age >10 is approximately 109 per 100,000 men per year and 36 per 100,000 women per year. Patients that have passed a first kidney stone have a 15% change of forming another stone within a year.
Signs and Symptoms
Symptoms of kidney stones often include the acute onset of one-sided flank or back pain that radiates toward the groin. The pain is typically very severe (comparable to giving birth) and characterized as colicky (comes and goes). Associated symptoms often include:
- Nausea & vomiting
- Blood in the urine
- Urinary frequency
Complications such as hydronephrosis and urinary tract infection may result in decreased urinary output, fever, abnormal smell/appearance of the urine, and burning on urination.
The diagnosis of kidney stones is suggested based on symptoms and physical examination, but typically confirmed with laboratory and imaging studies. Your doctor will usually obtain an ultrasound or CT scan of the abdomen to confirm the presence of nephrolithiasis and determine if there are any complications such as hydronephrosis or infection.
They will also typically order a urine analysis evaluating for blood, protein, pH, and signs of urinary infection. They may send your urine sample for bacterial culture. Commonly ordered blood tests include a CMP (comprehensive metabolic panel), and CBC (complete blood cell count), and uric acid level. They will also usually check your fasting and cholesterol levels and screen for diabetes.
One you pass a kidney stone; your doctor will typically send the specimen for stone analysis in order to determine the type of stone – this can guide therapy.
Kidney Stone Treatment
The acute treatment of kidney stones depends on the size of the kidney stone and if there are any complications. Most cases of kidney stones come to the emergency department. Stones less than 5mm are generally managed expectantly – meaning, your doctor will treat your pain and allow you to pass the stone on your own. They may initially provide you with intravenous fluids and narcotic pain medications such as Duramorph (morphine) or Dilaudid (hydromorphone). Upon discharge, they will often provide you with a short course of oral pain medications such as:
They may also prescribe you an alpha-blocker medication to dilate the urinary tract and promote stone passing. This typically includes the drug Flomax (tamsulosin).
Larger stones (>5mm) are typically treated with a procedure called lithotripsy – during this procedure, a urology specialist will use shock waves to break the kidney stone down into smaller particles that will pass. If your kidney stone is blocking off the kidney and ureter, your doctor may have to surgically place a transcutaneous nephrostomy tube. This is an external tube that allows your kidneys to drain urine. Once the ureteral obstruction is resolved, the nephrostomy tube can typically be removed.
Your doctor will also typically order stone analysis – this allows them to determine the precise type of kidney stone and how to tailor treatment.
Patients with kidney stones are generally recommended to drink 1.5-2L of fluids daily to prevent stone precipitation. Patients with calcium stones may benefit from use of thiazide diuretics such as Hydrodiuril (hydrochlorothiaze) and this increases calcium reabsorption the kidney. Those with hyperuricemia and gout typically benefit from uric acid lowering therapies such as Zyloprim (allopurinol). Some patients develop kidney stones from taking mega doses of vitamin C – vitamin supplementation should typically be discontinued in these individuals.
- Fwu CW, Eggers PW, Kimmel PL, et al. Emergency department visits, use of imaging, and drugs for urolithiasis have increased in the United States. Kidney Int 2013; 83:479. - https://www.ncbi.nlm.nih.gov/pubmed/23283137
- Smith-Bindman R, Aubin C, Bailitz J, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med 2014; 371:1100. - https://www.nejm.org/doi/full/10.1056/NEJMoa1404446
- Kourambas J, Aslan P, Teh CL, et al. Role of stone analysis in metabolic evaluation and medical treatment of nephrolithiasis. J Endourol 2001; 15:181. - https://www.ncbi.nlm.nih.gov/pubmed/11325090
The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.