Kidney Stone Basics by Siddhivinayak Hospital Maninagar Ahmedabad

Basic information by :: Basic information by :: Siddhivinayak Hospital, Siddhivinayak Hospital, Maninagar, AhmedabadManinagar, Ahmedabad

IntroductionIntroduction Conditions causing kidney stone formationConditions causing kidney stone formation Types of kidney stonesTypes of kidney stones

Calcium saltsCalcium salts Uric acidUric acid Mg ammonium POMg ammonium PO44

CystineCystine Other (xanthine, etc.)Other (xanthine, etc.)

Laboratory investigationsLaboratory investigations

Renal calculi (kidney stones) are formed in Renal calculi (kidney stones) are formed in renal tubules, ureter or bladderrenal tubules, ureter or bladder

Composed of metabolic products present Composed of metabolic products present in glomerular filtratein glomerular filtrate

These products are in high conc.These products are in high conc. Near or above maximum solubility Near or above maximum solubility

High conc. of metabolic products in High conc. of metabolic products in glomerular filtrateglomerular filtrate

Changes in urine pHChanges in urine pH Urinary stagnationUrinary stagnation Deficiency of stone-forming inhibitors in Deficiency of stone-forming inhibitors in

urineurine

High conc. of metabolic products in High conc. of metabolic products in glomerular filtrate is due to:glomerular filtrate is due to: Low urinary volume (with normal renal Low urinary volume (with normal renal

function) due to restricted fluid intakefunction) due to restricted fluid intake Increased fluid loss from the bodyIncreased fluid loss from the body Increased excretion of metabolic products Increased excretion of metabolic products

forming stonesforming stones High plasma volume (high filtrate level)High plasma volume (high filtrate level) Low tubular reabsorption from filtrateLow tubular reabsorption from filtrate

Changes in urine pH due to:Changes in urine pH due to: Bacterial infectionBacterial infection Precipitation of salts at different pHPrecipitation of salts at different pH

Urinary stagnation is due to:Urinary stagnation is due to: Obstruction of urinary flow Obstruction of urinary flow

Deficiency of stone-forming inhibitors:Deficiency of stone-forming inhibitors:

Citrate, pyrophosphate, glycoproteins Citrate, pyrophosphate, glycoproteins inhibit growth of calcium phosphate and inhibit growth of calcium phosphate and calcium oxalate crystalscalcium oxalate crystals

In type I renal tubular acidosis, In type I renal tubular acidosis, hypocitraturia leads to renal stoneshypocitraturia leads to renal stones

Calcium saltsCalcium salts Uric acidUric acid Mg ammonium POMg ammonium PO44

CystineCystine Other (xanthine, etc.)Other (xanthine, etc.)

80% of kidney stones contain calcium80% of kidney stones contain calcium

The type of salt depends onThe type of salt depends on Urine pHUrine pH Availability of oxalateAvailability of oxalate

General appearance:General appearance: White, hard, radioopaqueWhite, hard, radioopaque Calcium POCalcium PO44: staghorn in renal pelvis (large): staghorn in renal pelvis (large) Calcium oxalate: present in ureter (small)Calcium oxalate: present in ureter (small)

Causes of calcium salt stones:Causes of calcium salt stones:

Hypercalciuria:Hypercalciuria: Increased urinary calcium excretionIncreased urinary calcium excretion Men: > 7.5 mmols/dayMen: > 7.5 mmols/day Women > 6.2 mmols/dayWomen > 6.2 mmols/day May or may not be due to hypercalcemiaMay or may not be due to hypercalcemia

Hyperoxaluria:Hyperoxaluria: Causes the formation of calcium oxalates Causes the formation of calcium oxalates

without hypercalciuriawithout hypercalciuria Diet rich in oxalatesDiet rich in oxalates Increased oxalate absorption in fat Increased oxalate absorption in fat

malabsorptionmalabsorption

Primary hyperoxaluria:Primary hyperoxaluria: Due to inborn errorsDue to inborn errors Urinary oxalate excretion: > 400 mmols/dayUrinary oxalate excretion: > 400 mmols/day

Calcium oxalate stones

Treatment:Treatment: Treatment of primary causes such as Treatment of primary causes such as

infection, hypercalcemia, hyperoxaluriainfection, hypercalcemia, hyperoxaluria Oxalate-restricted dietOxalate-restricted diet Increased fluid intakeIncreased fluid intake Acidification of urine (by dietary changes)Acidification of urine (by dietary changes)

Calcium salt stones are formed in alkaline Calcium salt stones are formed in alkaline urineurine

About 8% of renal stones contain uric acidAbout 8% of renal stones contain uric acid May be associated with hyperuricemia (with or May be associated with hyperuricemia (with or

without gout) without gout) Form in acidic urineForm in acidic urine General appearance:General appearance:

Small, friable, yellowishSmall, friable, yellowish May form staghornMay form staghorn Radiolucent (plain x-rays cannot detect)Radiolucent (plain x-rays cannot detect) Visualized by ultrasound or i.v. pyelogramVisualized by ultrasound or i.v. pyelogram

Treatment:Treatment: Purine-restricted dietPurine-restricted diet Alkalinization of urine (by dietary Alkalinization of urine (by dietary

changes)changes) Increased fluid intakeIncreased fluid intake

Uric acid stones

About 10% of all renal stones contain Mg About 10% of all renal stones contain Mg amm. POamm. PO44

Also called struvite kidney stonesAlso called struvite kidney stones Associated with chronic urinary tract Associated with chronic urinary tract

infectioninfection Microorganisms (such as from Proteus Microorganisms (such as from Proteus

genus) that metabolize urea into genus) that metabolize urea into ammoniaammonia

Causing urine pH to become alkaline Causing urine pH to become alkaline and stone formationand stone formation

Commonly associated with staghorn Commonly associated with staghorn calculicalculi

75% of staghorn stones are of struvite 75% of staghorn stones are of struvite typetype

Treatment:Treatment: Treatment of infectionTreatment of infection Urine acidificationUrine acidification Increased fluid intakeIncreased fluid intake

Mg ammonium phosphate (struvite) stone

A rare type of kidney stoneA rare type of kidney stone Due to homozygous cystinuriaDue to homozygous cystinuria Form in acidic urineForm in acidic urine Soluble in alkaline urineSoluble in alkaline urine Faint radio-opaqueFaint radio-opaqueTreatment:Treatment:

Increased fluid intakeIncreased fluid intake Alkalinization of urine (by dietary changes)Alkalinization of urine (by dietary changes) Penicillamine (binds to cysteine to form a compound Penicillamine (binds to cysteine to form a compound

more soluble than cystine)more soluble than cystine)

Cystine stone

If stone has formed and removed:If stone has formed and removed:

Chemical analysis of stone helps to:Chemical analysis of stone helps to: Identify the causeIdentify the cause Advise patient on prevention and future Advise patient on prevention and future

recurrencerecurrence

If stone has not formed:If stone has not formed: This type of investigation identifies causes This type of investigation identifies causes

that may contribute to stone formationthat may contribute to stone formation Serum calcium and uric acid analysisSerum calcium and uric acid analysis Urinalysis: volume, calcium, oxalates and Urinalysis: volume, calcium, oxalates and

cystine levelscystine levels Urine pH > 8 suggests urinary tract infection Urine pH > 8 suggests urinary tract infection

(Mg amm. PO(Mg amm. PO44)) Urinary tract imaging:Urinary tract imaging:

Ultrasound and i.v. pyelogramUltrasound and i.v. pyelogram