Patient's question:
What factors or causes lead to kidney stones?Doctor's answer:
Hello! Formation Mechanism of Urinary Tract StonesUrinary tract stones form in the kidneys and bladder. The formation mechanism, etiology, stone composition, and epidemiology of upper urinary tract stones differ significantly from those of lower urinary tract stones. Most upper urinary tract stones are calcium oxalate stones. Magnesium ammonium phosphate stones are more common in bladder stones than in upper urinary tract stones. Although some kidney stones have clear factors or etiologies, such as hyperparathyroidism, renal tubular acidosis, nephrocalcinosis, gout, foreign bodies, prolonged bed rest, obstruction, and infection, the formation factors or etiologies of most calcium stones remain largely unexplained.
The three most fundamental theories of stone formation are nucleation, stone matrix, and crystal-inhibiting substances. Based on different formation mechanisms of upper urinary tract stones, they are categorized into metabolic stones and infectious stones. Metabolic stones result from metabolic disorders, such as hyperparathyroidism, hypercalciuria caused by various factors or etiologies, hyperuricosuria, and hyperoxaluria. High concentrations of chemical components damage renal tubules, leading to an increase in matrix substances in urine, precipitation of salts, and stone formation. Infectious stones occur when urease-producing bacteria decompose urea in urine, producing ammonia and alkalizing the urine. This results in a relatively supersaturated state of phosphates and uric acid ammonium in urine, leading to deposition. Bacteria, infection byproducts, and necrotic tissue also serve as cores for stone formation.
Many factors influence the formation of urinary tract stones. The salts that form stone crystals in urine are in a supersaturated state, insufficient inhibitory substances for crystal formation, and the presence of nucleating matrix are the main factors.
(1) Epidemiological factors include age, gender, occupation, socioeconomic status, dietary composition and structure, water intake, climate, metabolism, and genetics. Upper urinary tract stones are more common in people aged 20–50. Males are more affected than females, with the peak incidence in males at age 35. Females have two peaks at ages 30 and 55. During World War II, the incidence of upper urinary tract stones decreased, but it rose significantly during the intervening period and in the past four decades, suggesting a correlation with economic income and dietary structure changes. Experiments have shown that increased animal protein and refined sugar in the diet, along with reduced fiber, promote the formation of upper urinary tract stones. Drinking plenty of water dilutes urine, reducing crystal formation. Relatively high temperatures and reduced activity are also influencing factors, though occupation and climate are not singular determinants.
(2) Urinary factors:
1. Excessive excretion of stone-forming substances: Increased excretion of calcium, oxalate, and uric acid in urine. Conditions such as prolonged bed rest, hyperparathyroidism (reabsorptive hypercalciuria), idiopathic hypercalciuria (absorptive hypercalciuria—increased intestinal calcium absorption or renal hypercalciuria—decreased renal tubular calcium reabsorption), other metabolic abnormalities, and renal tubular acidosis all increase urinary calcium excretion. Gout, persistent acidic urine, chronic diarrhea, and thiazide diuretics increase uric acid excretion. Endogenous synthesis or intestinal absorption of oxalate can lead to hyperoxaluria.
2. Reduced acidity and increased pH.
3. Reduced urine volume, leading to higher concentrations of salts and organic substances.