SM 216 Kidney Stones Flashcards
How common are kidney stones?
Effect 1 in 10 people
Who gets kidney stones more often?
Men > Women, Asians and Caucasians, Stone Belt in the US
How does climate effect Kidney Stones?
Hot and dry climates promote water loss which facilitates kidney stone formation
What is supersaturation?
Supersaturation describes the process of crystal formation after the concentration of a substance improves the solubility threshold in solution, leading to precipitation out of solution and crystal formation
What is a stone nidus?
A stone nidus is a solid particle that facilitates crystal formation of other particles
What are the main determinants of solubility, and which ones are physiologically relevant?
Concentration of ion/compound, pH, and temperature
Temperature cannot be varied, so concentration’s of ions and pH are the physiologically relevant determinants
How does urinary pH effect the relative solubility of molecules?
High urinary pH increases the solubility of some molecules and decreases the solubility of others
Does high or low solubility of a substance facilitate stone formation?
Low solubility facilitates stone formation
Which solutes have a higher solubility at high urinary pH?
Cysteine and Uric acid, which are more likely to form stones at lower pH
Which solutes have a lower solubility at high urinary pH?
Ammonium Urate and Phosphate
Which molecules are more likely to form stones at low urinary pH?
Uric acid and Cysteine, because they have higher solubility at high pH
Which molecules are more likely to form stones at high urinary pH?
Ammonium Urate and Phosphate, because they have lower solubility at high pH
Which stones look like “square envelopes”?
Calcium oxalate
What is the most common type of kidney stone?
Calcium oxalate
What is the second most common type of kidney stone?
Calcium phosphate
What are the risk factors for calcium stones?
Hypercalciuria, Hyperoxaluria
What is the main risk factor for calcium stone?
Hypercalciuria
What can cause hypercalciuria?
Hypercalcemia (high serum Ca leads to high urine Ca)
Due to: hyperparathyroidism, malignancy, Vit D toxicity
May be idiopathic
Where can hyperoxaluria come from?
Dietary intake of high-oxalate food, Vit C intake, and low calcium intake
Why is Crohn’s disease a risk for hyperoxaluria?
Malabsorption in GI tract leads to increased oxalate reabsorption
How does low Calcium intake lead to hyperoxaluria?
Ca normally binds oxalate leading to less systemic absorption, so low calcium lowers oxalate sequestration and leads to more absorption, causing hyperoxaluria
What kind of stone appears as “coffin lids”?
Struvite stones (infection stones)
What makes up Struvite stones?
Magnesium ammonium phosphate
What are the risk factors for Struvite stones?
Alkalization of urine due to urease producing bacteria, which lowers the solubility of urinary phosphate-cation (Mg/Ca/NH4) complexes
Which bacteria is associated with Struvite stones?
Proteus spp
What are Staghorn calculi?
Very large Struvite stones that include more than one renal calyx, often due to Proteus spp
What type of stones show up as diamonds or rhomboids?
Uric acid stones appear as diamond or rhomboid stones
Which type of stones do now show up on X-Ray?
Uric Acid stones
What pH promotes Uric acid stones?
Acidic urine, which lowers the solubility of uric acid
What pH promotes Struvate stones?
Basic urine, which lowers the solubility of phosphate
What are the risk factors of Uric acid stones?
Hyperuricosuria, low urinary pH
What causes hyperuricosuria?
Dietary intake of purines and animal protein
High cell-turnover states which release uric acid
What are high cell turn-over states?
Hemolysis, tumor-lysis syndrome = rapidly dying cells release uric acid
What type of stones appear “hexagonal”?
Cysteine stones are hexagonal
What causes cysteine stones?
Cysteine stones are secondary to inherited disorders of metabolism, because patients can’t reabsorb Cysteine, raising concentration in the urine
What is the treatment for Cysteine stones?
Cysteine is insoluble at low pH, so treatment is alkalinizing the urine
What are general risk factors for stone formation?
Low urine volume
High Na diet
Hypocitraturia
High protein diet
Does low or high urine volume favor stone formation?
Low urine volume - raises the conc. of solutes which increase the probability of stone formation
How does high Na favor stone formation?
High Na diets result in high urinary Ca due to Na/Ca reabsorption in the PCT
How does hypocitraturia favor stone formation?
Citrate normally chelates ions and prevents stone formation with phosphate
How does a high protein diet favor stone formation?
High protein diets increase the acid load, which results in bone resorption since bone is a major buffer, raising calcium levels in serum and urine, favoring stones formation
What unexpected organ is a major buffer source?
The bone, at the cost of raising serum and urinary calcium
How does urinary flow effect stone formation?
High flow = less stone formation
Low flow = more stone formation
How do bacteria effect stone formation?
Sterile = less stone formation Infected = more stone formation
How does fluid intake effect stone formation?
High fluid intake correlates with lower risk of stone formation, especially above 2L/day
What is renal colic?
Renal colic is the acute presentation of kidney stones
How do kidney stones present?
Flank pain radiating to the groin
Extremely painful
No comfortable position
Hematuria
Do kidney stones cause hematuria?
Yes, both gross and microscopic
How are kidney stones differentiated from peritonitis?
Kidney stones do not have a position of comfort, while peritonitis does
How painful are kidney stones?
Kidney stones are on par with childbirth
What is the recommended way to diagnose kidney stones?
Non-contrast CT abdominal scan
Uric acid stones don’t show up on X Ray
What is the major determinant of whether or not a kidney stone will pass?
Stone size is the major determinant; stones < 5mm will likely pass on their own
Why might a kidney stone be treated instead of being allowed to pass?
Too large > 5mm
Pain control
Concurrent urinary/kidney infection or injury
What intervention can treat large kidney stones?
Extracorporeal shock-wave lithotripsy
What factor predisposes recurrent kidney stones?
Having a kidney stone predisposes another kidney stone
How are kidney stones managed long term?
24 hour urine collections for calcium, oxalate, sodium, uric acid, citrate, phosphate, pH to identify major risk factors for medical intervention
What are potential medical interventions for kidney stones?
Reduce hypercalciuria
Increase urinary pH and citrate
Assess medication list and address risk
How can hypercalciuria be treated?
Thiazide diuretics - stimulate calcium reabsorption at the DCT
What can increase urinary pH and citrate?
Potassium citrate supplementation - as part of kidney stone treatment
