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23 Cards in this Set
- Front
- Back
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Learning objectives
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Know basic epidemiology and demographic groups most likely to suffer from stones.
Understand the role of promoters and inhibitors in stone disease Understand the basic pathophysiology of calcium oxalate stones, uric acid stones, and cystine stones Understand basic treatment options |
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Highest risk for stones
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Middle Aged
White Males Sedentary American diet Stone belt |
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Stones: Pathophysiology
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Chemical equilibrium
-Concentration of stone constituents -Amount of water -pH Biochemical equilibrium -Urine is frequently supersaturated with stone constituents --Promoters vs inhibitors |
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Stone: Promoters
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Stents
Tamm-Horsfall mucoprotein Uric acid |
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Stone: inhibitors
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Complex with stone constituents
Increase solubility of small crystals Cover sites for further crystal growth Citrate Magnesium Glycosaminoglycans, chondroitin sulfate Uropontin |
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Calcium absorption
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Passive Ca absorption linked to sodium in PT
-65% Voltage dependent Ca absorption in TALH -20% Active Ca transport in DT -10-15% |
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Factors causing increased urine calcium
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Hyperparathyroidism
Sarcoidosis Antacids Vitamin A or D intoxication Distal RTA Idiopathic -Majority of patients |
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Oxalate metabolism
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Oxalate is a normal constituent of the diet
-Leafy greens, rhubarb, tea, chocolate Endogenous oxalate production -Metabolism of glycine and Vit C -Genetic defects causing hyperoxaluria |
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Calcium and calcium oxalate stones
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Low calcium diet is associated with INCREASED risk of stone formation
-Oxalate may be bound to calcium in the GI tract -Other factors associated with low calcium diet may be problematic. |
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Risk factors for calcium calculi
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Concentration of urine constituents
-Calcium -Oxalate -Urine volume pH -Acid pH results in calcium oxalate stones -Basic pH results in calcium phosphate Promoters -Uric acid Inhibitors -Citrate -Magnesium |
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Citrate
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Complexes calcium and is an important inhibitor of stone formation
Renal handling of citrate -Most citrate is reabsorbed proximally -An acidic environment favors citrate reabsorption -Hypokalemia favors citrate reabsorption |
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Hazards of a diet high in protein (6)
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Increased urine acid excretion
Increased urine sodium excretion Increased excretion of uric acid Decreased citrate excretion Increased cholesterol content Decreased potassium content |
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How can urinary oxalate be decreased
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Decrease exogenous oxalate
Calcium supplementation Magnesium supplementation Cholestyramine |
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Uric acid stones: three risk factors
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Decreased urine volume
Increased uric acid production Low urinary pH -Greatest risk -As urine pH increases, uric acid is in urate form which is very soluble. Low urine pH, uric acid is prevalent form and uric acid is not very soluble |
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Increased uric acid production
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Increased dietary intake of uric acid
-Sweetbreads, liver, pancreas Increased dietary intake of protein -Results in increased uric acid production -Results in decreased urinary pH Beer |
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Fructose
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Increases urinary oxalate excretion
Increases plasma uric acid Increases urinary uric acid Bad for stones, bad for gout, bad for obesity! |
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Cystinuria: pathogenesis
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Metabolic defect
Inability to reabsorb -Cystine -Ornithine -Arginine -Lysine Cystine is extremely insoluble -More soluble at higher pH’s -Thiola binds to cysteine Hexagon crystals |
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Struvite stones: overview
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Frequently Staghorn calculi
Magnesium Ammonium Phosphate Bacteria containing urease metabolize urea into ammonium carbonate, and this leads to very high urinary pH Seen in the setting of chronic UTI |
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Indications for stone removal
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Infected
Obstructing Painful |
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Diagnosis of stones
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Abdominal x-ray identifies 80% of stones
-Uric acid stones may be missed Ultrasound will identify most stones in the renal pelvis IVP requires significant contrast load High resolution CT of the abdomen without contrast is best test at present |
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Suggested workup after first stone passage (5)
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Careful history
-Dietary habits -Medication -Family history -Occupation and access to water PE -BP -Evidence of acromegaly, thyrotoxicosis -Gout Stone analysis Abdominal x-ray Laboratory studies -Electrolyte panel, calcium, albumin, phosphate -Urinalysis --pH --Crystalluria -24 hour urinary volume |
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Management of stones
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Increased fluid intake
Lower sodium and protein diet |
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Medical therapy of stones
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Thiazide Diuretics
-Increase Proximal Tubular Reabsorption of Calcium (for calcium stones) Allopurinol -Decreases urinary uric acid (for ca and uric acid stones) Increase urinary pH -For uric acid and cystine stones |
