Nephrolithiasis Flashcards
What are the signs and symptoms of a kidney stone?
Acute onset. Flank pain that radiates to testicles. Excruciating pain. Hematuria usually. Dysuria. N/V. Fever and chills.
T or F. Kidney stones are common with a lifetime risk of about 10%.
T
In which gender are kidney stones more common?
Men 2:1
What is the recurrence risk of kidney stones?
50% in 5-10 years
Which is more hazardous: small or large stone?
Small stone b/c they can pass into the ureters.
What are the 3 locations kidney stones are most susceptible to lodge?
- Ureteropelvic junction
- Pelvic brim aka iliac vessel crossing
- Bladder entry
What other disorders should be included in the differential Dx of this presentation?
Acute cholecystitis. Acute appendicitis. Diverticulitis. Cystitis. Pyelonephritis. Abdominal aortic aneurysm. Pancreatitis. Ureteral stricture. Musculoskeletal causes. Zoster. GYN causes. Clots. Papillary necrosis.
What do you look for in urinalysis when suspecting a kidney stone?
Hematuria (seen in 90%). Crystals suggest composition if present.
What do calcium oxalate crystals look like?
Envelopes
What is the best imaging study for Dx of a kidney stone?
Helical CT: detects stones as small as 1mm.
Why wouldn’t you do a plain x-ray to Dx a kidney stone?
It’s not sensitive or specific. Can’t see the stone sometimes. Will miss radiolucent stones.
What are the radiolucent stones?
Uric acid and indinavir stones.
What is the most common type of stone?
Calcium oxalate (65%). Then calcium phosphate alone (15%), struvite (10-15%), uric acid (3-5%), and lastly cystine (1-2%).
What size stones have a high likelihood of spontaneously passing?
<5mm
What size stones are unlikely to pass?
7+ mm
What 2 classes of medications increase the chance of passing a stone?
- Alpha-1-Adrenergic Antagonists (relaxes sphincter)
2. Calcium Channel Blockers
What is NNT?
Number Needed to Treat. If the NNT=4, this means that you will have to treat 4 patients in order to benefit one.
What percentage of kidney stones require invasive intervention?
15-20%
What are the 3 types of invasive intervention?
- Extracorporeal shock wave lithotripsy (ESWL)
- Ureteroscopy
- Percutaneous nephrolithotomy
What are possible complications of kidney stones?
Ureteral obstruction and/or infection.
Why do kidney stones form?
Supersaturation of urine leads to crystallization.
What determines supersaturation?
Concentration and solubility.
What determines concentration?
amt of solute divided by volume of solvent
What determines solubility?
Solute (salts), solvent (urine), and nidus.
What determines solubility of urine?
pH and endogenous inhibitors of stone formation.
What are the endogenous inhibitors of stone formation?
Citrate and urinary glycoproteins.
What is the major risk factor for developing calcium oxalate stones?
Hypercalcuria. Others: hyperoxaluria, alkaline pH, hypocitriuria, hyperuricosuria.
What causes struvite stones?
Infection w/ urease-producing bacteria (Proteus, Serratia, Klebsiella, Mycoplasma). Usually seen with urinary stasis. Also known as “infection stones.”
What are struvite stones composed of?
Layers of bacterial products and mineral. Magnesium ammonium phosphate.
Struvite stones can only form in what kind of urine?
Very alkaline urine. The urease elevates the urine’s pH.
T or F. There is a vicious cycle of pyelonephritis, calculi, and hydronephrosis in regards to struvite stones.
T
A struvite stone that has become quite large is called what?
Staghorn calculus
What do struvite crystals look like on urinalysis?
Coffin lids
What’s the key in preventing recurrence of struvite stones?
Preventing UTI’s.
What are the 2 risk factors for uric acid stones?
Hyperuricosuria and acidic urine.
What are the causes of hyperuricosuria?
Gout, eating animal protein, tumor lysis syndrome.
What causes cystine stones?
Cystinuria (rare AR disorder of dicarboxylic acid transport).
Solubility of cystine stones increases with what?
Alkaline urine pH
What drug can increase the solubility of cystine stones?
Penicillamine
T or F. Drugs rarely cause stone formation.
T
What are the drugs that can form stones?
- Triamterene
- Protease inhibitors (indinavir, atazanavir)
- Guaifenesin
- Silicate (overuse of antacids containing magnesium silicate)
- Sulfa drugs
What tests should be done in evaluating a patient with a kidney stone?
- Urinalysis (inc pH and culture)
- Serum electrolytes
- BUN and serum creatinine
- PTH level if elevated serum calcium
- Stone analysis when possible
- Recurrent stones req. 24h urine collection
What’s the most likely cause of recurrent stones?
Low urine volume
What can you do to prevent calcium oxalate stones?
Reduce Na and animal protein intake. Do NOT restrict calcium intake.
What can you do to prevent uric acid stones?
Reduce animal protein and potassium citrate.
What are the 6 general recommendations to prevent recurrent kidney stones?
- Increase fluid intake to maintain urine output of 2-3L/day
- Decrease animal protein intake
- Reduce dietary salt intake
- Maintain normal calcium intake
- Decrease dietary oxalate
- Cranberry juice (dec oxalate and phosphate excretion and inc citrate exc)
What follows sodium excretion?
Calcium excretion. Calcium moves with sodium. This is why reducing salt intake helps prevent stones.
How do you know if a 24h urine collection is complete?
Lean body weight multiplied by 10 for males/8.5 for females to approximate total creatinine in the 24h collection.
