1. 
   

   How do you diagnose nephrolithiasis?

   
   
2. 
   

   How should kidney stones be managed in the inpatient setting?

   
   
3. 
   

   What medical therapy facilitates stone passage?

   
   
4. 
   

   When is urology or nephrology consultation indicated?

   
   
5. 
   

   What follow-up and further testing is appropriate after discharge?

   
   
6. 
   

   What drugs and dietary therapies are helpful in the secondary prevention of kidney stones?

Kidney stones are one of the most common and most painful disorders of the urinary tract. This chapter reviews the epidemiology of kidney stones, the pathophysiology and risk factors for their development, the typical clinical presentation, the initial diagnostic evaluation, the acute, often hospital-based symptomatic treatment, followed by the outpatient management focusing on secondary preventive measures.

Nephrolithiasis is a common disorder that inflicts recurrent pain and significant morbidity onto a substantial portion of the population, including many young and otherwise healthy individuals. In the United States, approximately 5% of women and 10% of men experience a symptomatic episode before the age of 70, and the cumulative 10-year recurrence rate is estimated at 40% for women and 60% for men.

Regional variations in the frequency and nature of kidney stone disease exist within the United States, with an increased prevalence in the southeastern region of the country. This variation may be related to differences in climate and sunlight exposure, as well as dietary habits and beverage consumption. Kidney stones develop more frequently among Caucasians than African Americans. Stones in the upper urinary tract are frequently seen in industrialized countries and are associated with a more affluent lifestyle, including high animal protein consumption, gout, and traits of the metabolic syndrome, including hypertension, impaired glucose tolerance, increased waist circumference, high triglycerides, and low-high-density lipoprotein (HDL) cholesterol. Bladder stones are more commonly seen in developing countries and more frequently affect individuals with a poor socioeconomic status.

Patients with kidney stones typically present with renal colic, characterized by severe pain and autonomic symptoms such as lightheadedness, diaphoresis, nausea, and vomiting. The severity of symptoms often results in a visit to a hospital emergency room, frequently requiring hospitalization and absenteeism from work. In the United States, kidney stones account for more than 2 million outpatient visits, over 600,000 emergency room visits, and approximately 0.4% of hospital admissions. Additional costs may arise from complications, such as ureteral obstruction, pyelonephritis, and the need for stone removal by instrumentation, surgery, or extracorporeal shock wave lithotripsy (ESWL). Patients with recurrent stone disease also have a heightened risk of chronic kidney disease. The annual cost of kidney disease in the United States, including hospitalizations, professional charges, and lost productivity, exceeds $2 billion.

Kidney stones can form from a variety of substances excreted in the urine and frequently consist of two or more different substances (Table 251-1). Calcareous (calcium oxalate or phosphate) stones are by far the most common, accounting for over 80% of kidney stones. Metabolic defects leading to stone formation include hypercalciuria in over 65% of cases, and less frequently, hyperuricosuria, hyperoxaluria, hypocitraturia, or some combination thereof.

For a kidney stone to form, the concentration of a dissolved salt has to exceed its solubility in urine, a condition known as supersaturation. Supersaturation is favored by increased urinary excretion of stone-forming salts, optimal urinary pH (Table 251-2), and decreased urinary volume, which leads to increased urinary concentration. The presence of crystallization facilitators in the urine, such as uric acid, or the absence of crystallization inhibitors, such as citrate, also contributes to stone formation.

Risk factors for kidney stone formation can be divided into diet, stone-provoking conditions, stone-provoking drugs, and anatomic abnormalities. Dietary factors promoting nephrolithiasis include low fluid intake, which promotes urinary supersaturation, high sodium and animal protein intake, which promote hypercalciuria, and high oxalate intake, which promote hyperoxaluria. In addition, a family history of kidney stones and a personal history of gout also confer an increased risk of kidney stone disease.

Table 251-3 displays a selected list of stone-provoking conditions, stone-provoking drugs, and anatomic urologic abnormalities that have been associated with stone disease. Of note, roux-en-Y gastric bypass surgery, a common bariatric surgical procedure, is associated with increased intestinal absorption of oxalate and hyperoxaluria, resulting in a long-term risk of kidney stone formation. Major stone-provoking drugs include the antiretroviral agent indinavir, which crystallizes in the urine, and the anticonvulsant topiramate, which inhibits carbonic anhydrase.

Oxalobacter formigenes is an intestinal bacterium that produces an oxalate-degrading enzyme. The resulting increased intestinal degradation of oxalate may protect against stone formation. Lack of intestinal colonization with Oxalobacter formigenes is prevalent in recurrent calcium oxalate stone formers and is associated with hyperoxaluria.

Patients with kidney stones most often present to the hospital with renal colic. Others present with a urinary tract infection, impaired renal function from obstructive uropathy, or chronic kidney damage. Increasingly, incidental kidney stones are diagnosed on imaging studies in patients admitted to the hospital for other reasons.

Typical renal colic is characterized by the acute onset of severe pain that awakens the patient from sleep. Colic typically lasts for one to four hours, followed by gradual improvement. The patient may move ceaselessly, looking for a comfortable position, and may also suffer from nausea, vomiting, and sweating.