Urinary Stones - Types and Prevention Flashcards
General risk factors for stones
Too little water leads to too concentrated urine
Solid objects act as nuceli to start process
Randalls plaque
Ca phosphate concretion in renal tubule
Plaque erodes through urothelium
Stone deposits onto the exposed plaque
Risk factors for calcium oxalate stones
High levels of Ca (hypercalcemia or excess in urine only) or oxalate
Low urine levels of inhibitor (citrate or Mg)
High urine levels of uric acid…Ca Ox form on uric acid crystals
Causes of hypercalcuria
Excess absorption of Ca from intestine (Blood Ca only birefly or idiopathic)
Renal leak of Ca (blood abs same bc of increase absorption)
Met acidosis - bone demineralization
Causes of increase urine oxalate
Excess absorption ——most common
Vitamin C turns to oxalate in alkaline urine
Primary hyperoxaluria - rare auto rec…enzyme defect
Causes of increase oxalate absorption
Excess intake of foods
Dec levels of oxalobacter formigenes that degrades oxalate
Dec binding of oxalate in gut so more free to be absorbed
Oxalate binding in gut
Normal - oxalate binds to Ca and Mg and eliminated in feces…free is absorbed
If less calcium then more absorbed
Oxalate biding in colon clinical implications
Enteric hyperoxaluria (Celiac, crohn’s, CF)
Fat malabsorption - more fat in colon
Fatty acids bind Ca
More free oxalate
Ca oxalate vs Ca phopshate stones
High urine Ca is risk for both
Low pH - oxalate
High pH - phos
If stone over 20 20% Ca Phos
HyperPTH - Bone resorption means more HCO3 and phosphate
Excess Ca, HCO3 and phos excreted in urine
Urine has high pH, Ca, and phos
Distal RTA - imparied excreted of acid into the urine by the distal neprhon…high pH and urine Ca
Purine degradation - Humans
Adenosine and guanosine to xanthine
Xanthine to uric acid
No uricase enzyme so path ends with uric acid
Uric acid risk factors
Too much uric acid in the ruine
pH too Low –most important
Uric acid pKa 5.35
Low pH means more free uric acid and more precipitates
At pH 6.5, over 90% of uric acid is lowuble
Too much uric acid in the urine
Excess production
Uricosurics - decrease serum uric acid levels but increase urine uric acid levels
Red meat
Other random disorders
Struvite
Mg, ammonium phosphate
Solubility according to pH - more soluble in low
Some also contain calcium phosphate (also not soluble at high pH)
How do struite stones form
UTI with specific bacteria that have uease
Urease hydrolyzes urea into ammonium
Ammonium - 1 of 3 stone constituents…increased urine pH, hydrogen phspphate dissociated and leads to phsophate
ABove + Mg in urine —–srtuvite
Most common urea splitters
Proteus - P mirabillis is most common
Klebsiella
Pseudomonas
E coli (rarely)
Struvite stones Risk factors
UTI with urea splitting
UTI risks - female postmenopausal, catheter
Infection stones are likely to grow fast and fill colecting system (staghorn stone)
Cystinuria
Autosomala rec defecti n intestine and kideny tubule transport of cystine, ornithine, lysine and argiinine
Dec tubular reabsorpotion of cystine —-high urine levels —-stones
Can form multiple stones nad staghonrs
Cysitnuria dx
Urine cysteine level
Stone analysis
Classic hexagonal crystals in the urine
Tx of cystinuria
Keep cystine in solution
Drink h2O to have at least 1X nocturia
Drugs with SH replace 1 cystine…drug-cystine dimer more soluble
Tiopronin and D.penicillamine
General diet recommendations
Drink moe H2O
Drink more lemonade and OJ
LEss animaal protein because it increases Ca absorption and has purines (uric acid)
Dec sodium…less Na means less reabsorption of both Na and Ca
