Nephrolithiasis (Kidney Stones)
Terms in this set (41)
Crystalline structure in the urinary tract that can achieve sufficient size to obstruct the passage of urine from the kidney to the bladder
Risk factors for KS
2X for men compared to women; peak onset is third decade; whites more than other races; more common in southeast (dehydration due to heat)
Likelihood of recurrence
40% have second within 2-3 years, 75% within 7-10 years, 90% within 20 years
Types of KS
Most calcium, but others include uric acid, struvite, and cystine
Most calcium oxalate or mixed; few are calcium phosphorus
Causes of stone formation
Supersaturation or change in characteristic of solvent that results in precipitation
Hypercalcemia or renal abnormality
Main factor in calcium homeostasis
Causes of hypercalcemia
Increased enteric absorption due to high vitamin D (or high activation of vitamin D due to sarcoid, TB, or PTH; sarcoid and TB increase vitamin D due to macrophage activation; increased Ca mobilization from bone due to high PTH, acidosis, or immobilization
Calcium reabsorption profile
90% proximally, passive, linked to Na reabsorption; ROMK channels in TALH can be affected by calcium sensing receptors, so if serum Ca is too high, ROMK shut off, making lumen more negative and keeping calicum in the tubule
Causes of hyperuricosuria
Overproduction of uric acid (tumor lysis and release of K+ and uric acid, high purine intake, metabolic defects) or decreased uric acid excretion (CKD or volume contraction, which results in increased reabsorption of uric acid)
Caused by defect in AA transporter in apical PCT cells; isolated cystinuria is less common, caused by defect in Cys-specific transporter on basolateral; side of PCT cells
Solvent changes that favor KS formation
Volume, pH, urine [citrate], crystal nidus
Effects of pH on stone formation
In general, low pH favors crystallization (exceptions are struvite and calcium phosphate stones)
When do you get struvite stones?
UTI with urease-splitting bacteria; you get ammonia which both alkanizes the urine and can contribute to struvite structure
Most common UTI urease-splitting bacteria?
Proteus mirabilis and pseudomonas (note that E coli, which is the primary bacterium in most UTIs, is not urease splitting); other less common ones are staph and klebsiella
Main inhibitor of calcium crystal formation
Common citrate urine finding in calcium stone formers? What is this finding occasionally associated with?
Hypocitraturia; can be associated with metabolic acidosis and hypokalemia
What crystals often create a nidus for calcium oxalate stone formation? What are the implications of this?
Uric acid; patients with hyperuricosuria are at an increased risk of calcium oxalate stone formation
Why does pain in kidney stone come and go?
Cycles with urine peristalsis
What is the differential with flank/lower back pain radiating to the groin?
Kidney stone, ovarian cysts, ectopic pregnancy, testicular torsion, appendicitis, diverticulitis, bowel obstruction
Other symptoms to help with diagnosis of KS
History of stones, predisposing condition, hematuria/infection, "gravel" in urine
Results of kidney stone
Obstructive nephropathy (block in urine flow, uretal dilation, accumulating pressure); eventual renal failure (uncommon unless bilateral obstruction or solitary kidney)
Radiology to find stones
CT most common (though uric acid are not radioopaque!); can use; can also do contrast injection to look for blockage in urine drainage; ultrasound rare
Treatment for KS
Analgesic therapy, pass the stone (if under 5mm), interventional therapy
Follow up for KS
Urine studies (to ID crystals); metabolic eval; analysis of minerals, electrolytes, volume, pH of urine
Appearance of crystals - Calcum oxalate
Monohydrate looks like a dumbbell (need to lift dumbbells to be strong as an OX); dihydrate looks like an envelope with an X (oXalate)
Appearance of crystals - struvate
Looks like coffin lids
Appearance of crystals - cystine
Roundish like a cyst (hexagonal)
Appearance of crystals - uric acid
Management of kidney stones
Address urine solute concentrations that are above recommended range; correct characteristics of urine to favor stone precipitation
Dietary management of stones
Restrict oxalate if that is the problem, restrict purine intake if uric acid is problematic, DON'T reduce dietary calcium, won't help; decrease protein intake if urine pH is low; give bicarb or citrate supplement if urine citrate is low (but watch for Na counter ion)
How does high salt diet increase likelihood of calcium stone formation?
Reduced Na reabsorption in the PCT reduces calcium reuptake --> more urine calcium
Meds to help reduce KS?
Allopurinol to block uric acid production; thiazides to decrease urine calcium by contracting ECF and increasing Na reabsorption; tiopronin blocks cystine precipitation
What lifestyle modification and/or medical therapy would you use to treat low urine volume?
Increase fluid intake >2L/day
What lifestyle modification and/or medical therapy would you use to treat hypercalcuria?
Reduce Na, acid load; give thiazide
What lifestyle modification and/or medical therapy would you use to treat hyperoxaluria?
Oxalate restriction; Ca supplement with meals
What lifestyle modification and/or medical therapy would you use to treat hyperuricosuria?
Purine restriction; give allopurinol
What lifestyle modification and/or medical therapy would you use to treat cystinuria?
Protein restriction; give tiopronin
What lifestyle modification and/or medical therapy would you use to treat low urine pH?
Protein restriction; give potassium citrate supplement
What lifestyle modification and/or medical therapy would you use to treat low urine citrate?
Protein restriction; give potassium citrate supplement