Overview
Kidney stones are common and it is estimated that the lifetime incidence of developing a stone is in excess of 10%. Kidney stones occur when substances in the urine become too concentrated and form crystals which can develop into stones. The most common type of stone is calcium bound with oxalate and/or phosphate. Other stones include uric acid, struvite (infectious), cystine, and other more rare compositions.
There are many risk factors for urinary stone disease but the most common contributing factor is likely dehydration. The less urine that is produced increases the chance that crystals are produced from stone-forming materials. Other risk factors include diet, family history of stones, bowel disorders, obesity, and occupation. Diets that are high in animal protein, salt, or oxalate-rich foods (green leafy vegetables, nuts, tea, chocolate) may increase the risk of stone formation. Some bowel disorders include inflammatory bowel disease, malabsorption, chronic diarrhea, and those undergoing gastric bypass procedures.
Stones become a clinical problem when they become large enough to prevent drainage of urine from the kidney to the bladder. Occasionally, kidney stones can be a source of bacteria, causing recurrent urinary tract infections.
Symptoms
Kidney stones are often found incidentally for other reasons when not blocking the kidney. However, they can also cause severe pain if they suddenly block the kidney, most often when traveling down the ureter (the tube from the kidney to the bladder). The most common symptom for kidney stone is pain in the mid-back and side (flank). This pain can radiate to the front of the body below the rib cage, and down into the groin. The pain can be so severe as to cause nausea and vomiting, and the patient cannot find a comfortable position. Persons with kidney stones may have blood in their urine, and there may be pain with urination. Urinary frequency is common. A fever along with an obstructing stone can be a medical emergency and should be evaluated promptly.
Diagnosis
Diagnosis of kidney stones is often straightforward. The classic history given is that of acute onset of back or flank pain, with no particular precipitating event. There may be some blood in the urine. Definitive diagnosis consists of urinary tract imaging. A noncontrast CT (computed tomography) scan is the gold standard. Low-dose radiation protocols for CT imaging are in place in several hospitals to minimize radiation exposure. Renal ultrasound imaging can be used to identify obstruction and many stones are visualized as well. A urine specimen and blood tests are frequently obtained to check for infection and kidney function.
Treatment
Most kidney stones smaller than 5 mm can pass spontaneously. The size of the stone can be determined by a radiologic study. When a stone is in the ureter, medication can be given (medical expulsive therapy) to help the stone pass in order to avoid surgical intervention. If the stone is too big or does not pass on its own after a trial of passage, surgical treatments are available. Depending on several factors, options include ureteroscopy and laser lithotripsy, shock wave lithotripsy (SWL), percutaneous nephrolithotomy (PNL), and laparoscopic or open surgical removal.
Self Care
If a patient with a kidney stone is evaluated and found to have a stone that may pass spontaneously, it is recommended to maintain good hydration. Medical expulsive may be instituted with select medications. Prescribed pain medications should be taken before pain gets too severe since one may have some intermittent discomfort until the stone passes. If the patient cannot take fluids and medications because of nausea and vomiting, the patient may need to be admitted to the hospital and a temporary drainage tube (ureteral stent or nephrostomy tube) placed to relieve the blockage. In this setting, the stone may or may not be able to be treated at the same time.
Depending on risk factors, stone composition, and further work-up if necessary, medication may be prescribed to reduce stone formation in the future. All stone formers should drink lots of fluids to maintain a urine output of 2 Liters or more per day. Other general recommendations may be to restrict salt intake, to moderate animal meat and oxalate-rich foods, consume the normal recommended intake of calcium. Do not avoid calcium, even with calcium-based stones, unless your doctor recommends this as it may actually increase your risk of stones.
