Nephrolithiasis: Overview and Risk Factors

Nephrolithiasis is characterized by the formation of crystalline aggregates (“kidney stones”) that can develop anywhere along the urinary tract. Kidney stones are common in Western societies; nearly 10% of Americans will develop a symptomatic kidney stone during their lifetime.

The 5 major stone compositions are calcium oxalate, calcium phosphate, magnesium ammonium phosphate (struvite), uric acid, and cystine. Calcium–based stones are the most common, causing more than 75% of cases, and calcium oxalate is the most common type of stone overall. A rare but increasingly recognized cause of nephrolithiasis is the use of the protease inhibitor indinavir in treating HIV patients.

Most often, stones are due to increased concentrations of stone–forming material in the urine, either from increased excretion or decreased urinary volume. Stone formation occurs when a stone–forming material becomes supersaturated in the urine and begins the process of crystal formation.

Severe flank pain, known as renal colic, occurs with stones that become lodged in the ureter. It may radiate to the lower abdomen, groin, testicles, or perineum. Lower urinary tract symptoms, including dysuria, urgency, and frequency, occur with stones that become lodged at the ureterovesical junction. Nausea, vomiting, hematuria, and costoverterbral angle tenderness may also be present, even in the absence of pain.

Risk Factors

• Male gender. Males are 3 times more likely to develop stones than females.
• History of nephrolithiasis. Individuals who have developed a kidney stone have an 80% chance of recurrence within 10 years.
• Geography. Areas of elevated temperatures and high humidity appear to have an increased incidence of stone disease.
• Nationality. Developing countries have a much lower risk of nephrolithiasis, compared with developed countries. This is presumed to be due to dietary factors, specifically the absence of a Western–style, meat–based diet.
• Obesity. Compared with persons at or near ideal body weight (BMI = 21–23), obese men (BMI ≥30) have a 33% greater risk for stone formation, while obese women have a 200% greater risk.¹
• Diet. Diet plays an important role in nephrolithiasis risk, as described below in Nutritional Considerations.
• Family history of nephrolithiasis. Patients with a family history of kidney stones have a 2 to 3 times higher risk.
• History of cystinuria. Cystinuria is an autosomal recessive disorder that increases risk of cystine stone formation.
• Urinary stasis (eg, bladder outlet obstruction).
• Chronic urinary tract infections.
• Dehydration (eg, diarrhea).