Nephrolithiasis Flashcards
Are kidney stones more common in men or women?
Men, up to 16% of men and 8% of women will have at least one symptomatic stone by age 70
When does crystallization occur?
when concentration exceeds solubility product/point
What is the basic definition of concentration?
Concentration is just the quotient of amount of solute divided by the volume of solution.
Anything that increases the amount of solute and/or
decreases urine volume will increase concentration and therefore the propensity to stones.
Conversely, any interventions that decrease urinary solute concentration will decrease the likelihood of stone formation.
Factors that promote increased tubular solute conc.
- Increased filtered load,
- decreased tubular reabsorption, and/or
- increased water reabsorption.
What is Cystinuria?
A genetic disorder of cystine reabsorption in the renal tubules.
How common are Cystine stones?
Cystine stones are not common, occurring in 1‐2% of stones seen in adults and 5% of stones in children.
Still, these are important not to miss because, when untreated, cystinuria can lead to loss of kidney function.
What is a major determinant of solubility for the common forms of stones?
urine pH. Always look at the urine pH in stone‐formers!
What are some common inhibitors to stone formation?
-citrate (for calcium stones)
-urinary glycoproteins, such as Tamm‐Horsfall
mucoproteins
-nephrocalcin, and uropontin.
As you can imagine, anything that reduces the
concentration or effectiveness of an inhibitor will tend to increase stone formation, whereas repletion of an inhibitor might be an effective therapeutic adjunct.
Where are Tamm-Horsfall mucoproteins made?
(also called uromodulin), produced in the thick ascending limb of the loop of Henle
The presence of foreign bodies of any type will further favor development of
stones. Why?
For example, patients with a propensity to calcium stones often have a propensity to form uric acid stones. In these patients, it is not uncommon to find that calcium stones may form around a uric acid nidus.
Similarly, evidence suggests that some stones develop around nanobacteria that inhabit the upper urinary tract.
When concentration exceeds solubility, crystals can develop anywhere within the urinary tract. Where are they most likely to form?
They are most likely to develop into stones in areas where urine flow rates are low, as this allows time for growth.
What are these spots of low urine flow rate?
In the calyces and pelves instead of forming in the ureters.
This is also why stones are more likely to form
in areas of obstruction. For similar reasons, stones can also form in the bladder, particularly in the presence of obstruction and/or foreign bodies.
What are some common types of kidney stones?
- calcium oxalate (60%)
- calcium phosphate (15%)
- Mg-ammonium phosphate (struvite) (15%)
- uric acid (10%)
- cystine (1%)
- drugs (rare)
If a stone forms due to calcium overload, what should be the appropriate therapy?
avoid Ca++ supplements, BUT do not restrict dietary calcium intake
thiazides
sodium restriction and increased fluids
What urinary pH promotes CaOx stone formation?
pH independent
