Key Clinical Questions
How are kidney stones diagnosed?
How should kidney stones be managed in the inpatient setting?
What medical therapies facilitate stone passage?
When is urology or nephrology consultation indicated?
What follow-up and further testing is appropriate after discharge?
What drugs and dietary therapies provide secondary prevention of kidney stones?
Kidney stones inflict recurrent episodes of excruciating pain and significant morbidity on a substantial portion of the population, including many young and otherwise healthy individuals. In the United States, the current lifetime incidence of nephrolithiasis is 13% for men and 7% for women. Without treatment, the 5-year recurrence rate following an initial episode is up to 50%. A recent report from the National Health and Nutrition Examination Survey for the period of 1994 to 2010 describes a 70% increase in prevalence of self-reported kidney stones, extending across men and women of all age groups.
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 components of the metabolic syndrome, including hypertension, impaired glucose tolerance, increased waist circumference, high triglycerides, and low-high-density lipoprotein 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, often 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. Complications may arise, such as urinary tract obstruction and pyelonephritis, or 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. In the year 2000, the annual cost of kidney stones in the United States, including hospitalizations, professional charges, and lost productivity, was estimated at $5.3 billion.
PATHOPHYSIOLOGY AND RISK FACTORS
Kidney stones can form from several substances excreted in the urine, and frequently consist of two or more different substances (Table 243-1). Calcareous (calcium oxalate, phosphate, or mixed) 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.