NC.com

Stone Prevention

Fluid recommendations

• Drink more water: maintain UOP 2-3L to dilute salts and other stone forming agents, do not need to titrate to color
• Fluid type: water is best, caffeine/alchol are fine, juice is fine, milk is fine, dark sodas (contains phosphoric acid) are worst
• Alkaline water: alkalinity means ability to buffer against acids (not a measure of how basic/high pH the water is), baking soda and moonstone powder provide most alkali, no "alkaline waters" provide adequate buffering

Food recommendations

• Eat less salt: salt reabsorption in the tubule decreases calcium reabsorption, limit salt intake to < 2.3g daily (100mEq)
• Eat less meat: protein = amino acids -> high urinary acid load, all meat (mammal, bird, fish, etc) are equal, can also increase calcium excretion
• Oxalate-containing foods: only avoid if proven hyperoxaluria, likely due to enteric causes
• Vitamin C (absorbic acid): can be converted to oxalate, avoid high doses
• DASH diet: shown to decrease stone formation despite having increased oxalate content

Juice

• Rationale: contains citric acid, which is converted to citrate and bicarbonate, main benefit is alkalinization not citrate
• Citrate level: grapefuit has the highest (197.5mEq/L), then orange then lemon
• Potassium: grapefruit and orange both contain potassium in addition to citrate, lemon juice does not
• Vitamin C: although citrus juice contains vitamin C (converted to oxalate), overall risk of increased oxalate level is minimal (juice benefits outweigh risks)

Calcium balance

• Low calcium diet: leads to uninhibited oxalate gut absorption, urine shows lower calcium and increased oxalate (Borghi 2002)
• Calcium supplementation increases calcium stone risk
• Maintain normal calcium levels: 1000mg/d for women < 50 and men < 70, otherwise 1200mg/d
• Limit sodium < 100mEq/d (sodium increases calcium retention)

Cystinuria management

• Fluid intake: > 3L urine output per day
• Diet: minimize methionine intake (converted to cystine), minimize sodium intake
• Alkalinization: KCit 60-90mEq TID-QID, NaBicarb is good alternative (cystine solubility only increases above pH of 7), risk of CaPhos stones
• Medications: tiopronin (Thiola) 800-1500mg/d (divide into 3 doses), penicillamine 0.5-2g/d (divide into 3-4 doses), captopril (after failing thiol therapy)

Management based on metabolic workup parameters

Dehydration	Hypercalcuria	Hypercalcemia	Hypernatruria	Hyperuricosuria	Low urinary pH	Hypocitraturia	Hyperoxaluria	Stone composition	Other findings	Diagnosis	Management
Yes	-									Dehydration	Increase fluid intake to 2-3L
No	Yes	Yes	No	-				CaPhos	HyperPTH	Resorptive hypercalciuria	Parathyroidectomy
		No						-		Hypercalciuria	Thiazide diuretic
			Yes							Hypernatriuria	Limit sodium intake
No				Yes	Yes	-		Calcium	-	Hyperuricosuria	Hydration Alkalinization
								Uric acid
					No			-	Hyperuricosemia	Various causes	Treat underlying cause Allopurinol
No					No	Yes	-			Hypocitraturia	KCit supplement
					No (increased)		-	CaPhos	Hypokalemia/Hypochloremia	Type I RTA	KCit + Hydration
No							Yes	-		Hyperoxaluria	Limit dietary oxalate Consider B6 supplement
No								Struvite	Urease-splitting bacteria	UTI/Struvite stones	Complete stone removal Acetohydroxamic acid
								Cystine	Cystinuria	Cystinuria	Hydration Alkalinization Thiola
								Ammonium acid urate	Radiolucent	Chronic diarrhea	Check for chronic diarrhea causes
								Xanthine		Xanthinuria	Check for mutation vs allopurinol use
								Hypomagnesiuria	-	Hypomagnesiuria	Magnesium supplements
								Calcium	Otherwise normal	Idiopathic stone formation	KCit supplements

Medications

Class	Mechanism	Indication	Side effects	Dosing
Thiazide diuretics	distal tubule calcium resorption, sodium excretion	Hypercalciuria, calcium stones	Hypokalemia (may need supplements), hyperuricosuria, hypercalcemia, hyperglycemia, hypocitraturia (secondary to intracellular acidosis), tachyphylaxis	HCTZ 25mg BID Chlorthalidone 25mg QD Indapamide 2.5mg QD
Potassium citrate (KCit)	Increases urinary citrate, alkalinizes urine, binds urinary calcium	Calcium stones, low urinary citrate, Type I RTA, chronic diarrhea (use liquid form), thiazide-induced hypocitraturia, HU < 500	GI symptoms, hyperK (requires regular monitoring), increased CaPhos risk, wax coating passes in stool	20mg BID-TID
Calcium supplements	Prevents oxalate absorption, maintains normocalcemia	Hypocalcemia, hyperoxaluria - test on and off supplementation	Increases calcium stone risk	500-600mg CaCarb BID
Sodium bicarbonate Sodium citrate	Increases urinary citrate, alkalinizes urine	KCit replacement if hyperkalemia risk	Hypernatremia	650-1300 mEq QD-BID
Allopurinol (Zyloprim)	Inhibits uric acid production	Calcium stones in setting of hyperuricosuria (> 800/day) and normal calcium, do not give for uric acid stones	Transaminitis, rash, myalgias Check baseline and 1mo LFTs	300mg daily
Alpha-mercaptopropionylglycine (Thiola)	Inhibits formation of insoluble cystine bond	Cystinuria	Transaminitis, anemia, asthenia, GI distress, rash	300mg BID, titrate up PRN
Acetohydroxamic acid (Lithostat)	Urease inhibitor	Struvite stones that cannot be managed surgically	Phlebitis/DVT, hemolytic anemia (3-15%), hypercoagulable state, tremor, headache, rash, palpitations, GI distress, alopecia	250mg BID-TID
Magnesium oxide	Increases calcium and phosphate solubility	Hypomagnesiuria	Diarrhea, hypermagnesiuria in renal insufficiency	140gmg QID or 400-500mg BID