SM 216: Kidney Stones

Question 1

What is the epidemiology of kidney stones?

Answer 1

More prevalent in men than women, prevalence increasing over time (maybe due to diet)
Geographic Variability: higher prevalence in Southern USA - hotter/dryer - more dehydration - more risk of kidney stone
Racial Variability: Higher risk in Asians and Caucasians

Question 2

What is the pathogenesis of kidney stones?
What is a Stone Nidus?
What conditions cause stones of what substance?

Answer 2

Supersaturation - when substance conc. exceeds it’s solubility threshold, it precipitates out of solution and forms crystals (forms faster when other solid particles present - called STONE NIDUS)
Solubility determined by Concentration, pH, Temperature
Phosphate + Ammonium Urate: lower solubility as urine pH increases (precipitates at basic pH)
Uric Acid + Cystine: lower solubility as urine pH decreases (precipitates at acidic pH - less likely)

Question 3

Calcium Containing Stones

Shape, Prevalence, Risk Factors

Answer 3

Square Envelopes
MOST Common kidney stone in US (Ca Oxalate): 75-80%
Risk: 1. Hypercalciuria (Idiopathic or 2/2 Hypercalcemia - Primary hyperparathyroidism (high PTH), malignancy, vitamin D toxicity, Sarcoidosis)
2. Hyperoxaluria: High diet intake of oxalate (chocolate, spinach, berries, nuts), high vitamin C intake (metabolized to oxalate), malabsorption in GI (Chron’s Disease, Celiacs), Low Ca Diet Intake = less oxalate binding in gut = more oxalate absorption into blood, primary hyperoxalosis - genetic basis for high oxalate)

Question 4

Struvite Stones and Staghorn Calculi
(Shape, Prevalence, Composition, Risk Factors)

What are staghorn calculi?

Answer 4

Coffin Lids
2nd Most common 10-12% all stones
“Triple P Stones” - Mg Ammonium Phosphate or Ca Carbonate Apatite
Risk: 1. Urease Producing Bacteria alkalinizes urine - lowers phosphate solubility - complexes with surrounding ions (PROTEUS SPP)
Staghorn calculi: Large stones that grow into multiple calyces - seen on radiograph

Question 5

Uric Acid Stones

Shape, Prevalence, Risk Factors

Answer 5

Diamond/rhomboid shape - least typical
3rd most common (7-9%) more common in certain geographies due to different diets
RADIOLUCENT ON XRAY (CAN BE MISSED), form stones in ACIDIC pH!
Risk Factors: 1. Hyperuricosuria: high urine uric acid due to high dietary intake of purines/animal proteins (break down to uric acid) or high cell turnover states (high uric acid in cells; hematologic malignancies - hemolysis or tumor lysis syndrome)
2. Low urinary pH

Question 6

Cysteine Stones

Shape, Prevalence, Risk Factors

Answer 6

Hexagonal Shape - PATHOMNEMONIC
RARE stones
Risk: 2/2 genetic disorder of cysteine metabolism - can’t reabsorb cysteine in urine so it builds up
1. low pH causes less solubility

Question 7

Risk factors for Kidney Stones

Answer 7

1. Low urine volume
2. High Na Diet (less Na R = less Ca R in PT)
3. Hypocitraturia (citrate inhibits stone formation)
4. High Protein Diet (high acid load = high buffer source from bone = high Ca in blood from bone = high urine Ca)
5. Less urinary frequency
6. Bacterial infection
7. Low pH (except struvite)
8. Low fluid intake

Question 8

What is the acute presentation of a kidney stone?

how are kidney stones dx?

Answer 8

Renal Colic: Flank + R/LLQ abd pain radiating to groin, extremely painful, cannot find comfortable position, hematuria

Dx: non-contrast CT abdomen (can miss uric acid stones!)

Question 9

Kidney Stones: Likelihood of passing, Acute Tx, Complications, Interventions

Answer 9

Stone passes if <5mm; won’t pass if >1cm
Acute tx: Pain control + hydration
Complications: concurrent urinary/kidney infection (increases risk of spread; post-renal AKI
Interventions: Extracorporeal Shock-Wave Lithotripsy (ESWL) - crush stone into bits;
Percutaneous Nephrolithotomy: surgical extraction = less common

Question 10

Long-Term Management of Kidney Stones

Answer 10

Use 24hr urine collection to identify risk factors (Ca, oxalate, Na, uric Acid, phosphate, Cr, total volume, pH)
LithoLink company helps identify abnormalities

Aggressively manage diet/meds to fix abnormalities

Question 11

Potential medical interventions for kidney stones

Answer 11

1. Thiazide Diuretic: blocks NCCT - more Ca reabsorption = less hypercalciuria
2. Potassium Citrate Supplement: raises urine pH (good for uric acid/cysteine) and more citrate inhibits stone formation
3. Address risk of current medication use

Question 12

Three Key General Kidney Stone Management Guidelines

Answer 12

1. High Fluid Intake (dilute urine)
2. Balanced Diet (normal Ca - low Ca causes hyperoxaluria, Low Na, Low Animal Protein)
3. Lifestyle - good BMI, less stress, good exercise