Urinary Stones - Types and Prevention

Question 1

General risk factors for stones

Answer 1

Too little water leads to too concentrated urine

Solid objects act as nuceli to start process

Question 2

Randalls plaque

Answer 2

Ca phosphate concretion in renal tubule

Plaque erodes through urothelium

Stone deposits onto the exposed plaque

Question 3

Risk factors for calcium oxalate stones

Answer 3

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

Question 4

Causes of hypercalcuria

Answer 4

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

Question 5

Causes of increase urine oxalate

Answer 5

Excess absorption ——most common

Vitamin C turns to oxalate in alkaline urine

Primary hyperoxaluria - rare auto rec…enzyme defect

Question 6

Causes of increase oxalate absorption

Answer 6

Excess intake of foods

Dec levels of oxalobacter formigenes that degrades oxalate

Dec binding of oxalate in gut so more free to be absorbed

Question 7

Oxalate binding in gut

Answer 7

Normal - oxalate binds to Ca and Mg and eliminated in feces…free is absorbed

If less calcium then more absorbed

Question 8

Oxalate biding in colon clinical implications

Answer 8

Enteric hyperoxaluria (Celiac, crohn’s, CF)

Fat malabsorption - more fat in colon

Fatty acids bind Ca

More free oxalate

Question 9

Ca oxalate vs Ca phopshate stones

Answer 9

High urine Ca is risk for both

Low pH - oxalate
High pH - phos

Question 10

If stone over 20 20% Ca Phos

Answer 10

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

Question 11

Purine degradation - Humans

Answer 11

Adenosine and guanosine to xanthine

Xanthine to uric acid

No uricase enzyme so path ends with uric acid

Question 12

Uric acid risk factors

Answer 12

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

Question 13

Too much uric acid in the urine

Answer 13

Excess production

Uricosurics - decrease serum uric acid levels but increase urine uric acid levels

Red meat

Other random disorders

Question 14

Struvite

Answer 14

Mg, ammonium phosphate

Solubility according to pH - more soluble in low

Some also contain calcium phosphate (also not soluble at high pH)

Question 15

How do struite stones form

Answer 15

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

Question 16

Most common urea splitters

Answer 16

Proteus - P mirabillis is most common

Klebsiella

Pseudomonas

E coli (rarely)

Question 17

Struvite stones Risk factors

Answer 17

UTI with urea splitting

UTI risks - female postmenopausal, catheter

Infection stones are likely to grow fast and fill colecting system (staghorn stone)

Question 18

Cystinuria

Answer 18

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

Question 19

Cysitnuria dx

Answer 19

Urine cysteine level

Stone analysis

Classic hexagonal crystals in the urine

Question 20

Tx of cystinuria

Answer 20

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

Question 21

General diet recommendations

Answer 21

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