The prevalence of kidney stones in the United States varies with race, sex, and geographic location. For men, rates vary from four to nine percent, and for women, stone rates range from almost two to four percent. The incidence of nephrolithiasis tracked by the Mayo Clinic indicates an increase in stone frequency since 1950 (1). For men, the rates of new stone appearance increased from 78.5 to 123.6 cases per 100,000 per year during this time. For women, in 1974 the rate was 36 cases per 100,000 per year. Caucasians are at a risk for stone formation that is several times that of African-Americans.

Recurrence rates of new stone formation are high. Estimates from long-term follow-up of 20 to 30 years indicate recurrence rates as high as 75%; with 40% to 50% of the recurrences occur within five years of the initial stone (2). While there is variation in the natural history of stone disease, patients who have formed two or more stones tend to have successive shorter intervals between stones (3). The accelerating pace of stone formation in recurrent stone formers cannot be predicted by their metabolic abnormality, sex, age, or any other known characteristic. Therefore, in any single stone-former, one cannot predict who will relapse. This complex natural history of stone disease and the high rate of recurrence is the basis for careful diagnostic evaluation and early treatment.

An episode of renal colic has a sudden onset, with fluctuation and intensification over 15 to 45 minutes. The pain then becomes steady and unbearable and often accompanied by nausea and emesis. As the stone passes down the urinary tract toward the bladder, the flank pain changes in a downward direction toward the groin. As the stone lodges at the ureterovesical junction, urinary frequency and dysuria appear. The pain may clear as the stone moves into the bladder or from the calyceal system into the ureter.

Stones may obstruct the urinary tract and impair renal function. There is increased risk of infection with chronic obstruction. Bleeding may be chronic and accompany obstruction. The presence of bleeding alone does not predict a more severe outcome. Episodes of rapid onset of pain, bleeding, and then rapid clearing, often called ‘passing gravel’, is the result of passing a large amount of crystals of calcium oxalate, uric acid, or cystine.

The size, number, and metabolic composition of new stones strongly influence the natural history and complication rates. Thus, the clinical presentation can be classified by metabolic type (Table 2). Spontaneous stone passage may occur with calcium oxalate, calcium phosphate, uric acid, and cystine stones. Rarely does a struvite stone or staghorn stones of other composition (cystine, uric acid) pass spontaneously.

All patients with a stone or suspected of stone in the urinary tract should undergo an imaging procedure to determine new stone formation, or metabolic activity. Localization of stones is also important in planning the surgical approach or use of lithotripsy. Noninfused CT of the abdomen with 5 mm cuts is the most sensitive imaging technique for determining the number and location of stones within the renal parenchyma or along the upper or lower urinary tract. Using this technique, stones can be distinguished from kidney tissue or blood clots. Nephrocalcinosis can be identified as a myriad of tiny, almost microscopic specks of radiodense calcium arrayed along the calyces. Small, separate, radiodense stones of less than 1 cm in diameter suggest calcium stones, or occasionally, cystine stones (Table 2). Radiodense stones suggest either calcium or struvite composition, but struvite stones are usually large and fill the calyceal system. Cystine stones appear to be radiodense, but less dense than calcium-containing stones. Small, radiolucent stones suggest uric acid composition. Uric acid stones appear as filling defects on intravenous pyelography. Filling defects that occupy the renal pelvis are staghorn stones and may be of struvite, uric acid, or cystine composition. Sludge may be of either uric acid or cystine, can fill the renal pelvis, and cause obstruction. Plain radiographs of the abdomen can identify large stones of greater than 3 mm. Ultrasound may not accurately visualize all stones and therefore cannot be used for follow-up to determine the appearance of new stones.

Treatment to prevent recurrence of stones is based upon knowledge of the pathogenesis of the metabolic environment favorable for crystal formation, aggregation, and growth of the crystal mass. The metabolic abnormality is reflected in the composition of the stone, and is identified by selected blood and urine tests. Thus, every effort should be made to recover the stone for composition analysis. The frequency and composition of stones are listed in Tables 1 and 2. Urinalysis conducted on a first morning sample can reveal the presence of crystals and therefore the type of stone (Table 1).

The composition of every stone should be determined. Commercial laboratories can perform analysis using polarization microscopy with minimal expense. Infrared and spectroscopy and x-ray diffraction are more precise and sensitive, but are not necessary for most stone analyses.

The NIH Consensus Conference of 1988 recommended that a single stone former should undergo blood tests to detect primary hyperparathyroidism, other causes of hypercalcemia, and decreased renal function. At least one set of blood measurements and one 24 hour urine collection should be obtained on recurrent stone formers. The University of Chicago Kidney Stone Clinic obtains three 24hour urine collections and three consecutive fasting blood tests while the patients follow their usual diets. Each serum and urine collection (Table 3) is analyzed for calcium, phosphate, magnesium, creatinine, uric acid, and in one sample, sodium and potassium. In addition, each of the three urine collections is analyzed for citrate, oxalate, pH, and volume. A screening test for cystine is also performed on one urine sample from each patient.

Current management of stones in the renal parenchyma, collecting system, and urinary tract is based upon proposed general guidelines that emerged from the 1988 National Institutes of Health Consensus Conference on Nephrolithiasis (5, 6).

Surgical intervention is required for stones that cause obstruction, bleeding, severe pain, or serious infection. Depending upon size and location, stones may be removed using cystoscopy, lithotripsy, or percutaneous nephrolithotomy. Stones that are less than 5 mm in diameter may pass through the upper and lower urinary tract spontaneously, whereas those 7 mm and greater in diameter tend not to pass. Extracorporeal shock wave lithotripsy (ESWL) fragments stones in the renal parenchyma, and upper and lower urinary tracts. ESWL is effective for removing stones less than 2 cm in diameter, with success rates highest in kidneys that contain one stone. Stones less than 2 cm in the upper two-thirds of the ureter can be effectively fragmented, and cystoscopy is effective in removing stones in the lower one-third of the ureter. Stones lodged at the ureteropelvic junction or within calyceal diverticulae in the upper tract are best removed through endourologic techniques. Because too many shock waves may result in renal damage, very large stones and staghorn calculi are not treated with ESWL. Ureterolithotomy rather than ESWL is the procedure of choice for removal of stones in the lower segment of the ureter. Patients with stones larger than 2 cm require both ESWL and percutaneous nephrolithotomy. Overall, ESWL alone fails to remove stone fragments in 35% to 55% of cases. The special case of large, infected staghorn calculi, or complex anatomy, or obstruction, may require open surgery.