- Hypercalciuria is the most common metabolic abnormality identified in calcium stone formers.
- Citrate is the most important inhibitor of calcium oxalate stone formation; it complexes calcium and inhibits crystal growth.
- Randall plaques (calcium apatite) originate in the basement membrane of the thin loops of Henle and serve as the anchoring site for idiopathic calcium oxalate stone formation.
- Type 1 (distal) RTA is the most common form of RTA and most commonly associated with kidney stones (up to 70% of adults with type 1 RTA have stones); calcium phosphate is the most common stone composition.
- The 3 main determinants of uric acid stone formation are low urine pH (<5.5, most important), low urine volume, and hyperuricosuria.
- Cystinuria is autosomal recessive (SLC7A9 or SLC3A1) and causes impaired reabsorption of Cystine, Ornithine, Lysine, Arginine (COLA).
- Struvite stones only form in association with urea-splitting organisms (Proteus most common); they commonly produce staghorn calculi.
- Radiolucent stones on plain film include uric acid, matrix, xanthine, triamterene, 2,8-dihydroxyadenine, and indinavir.
- Non-contrast CT is the most sensitive imaging modality for stones (sensitivity 95%, specificity 98%).
- Ultrasound is the preferred imaging modality for stones in pregnancy; MRI is second-line when US is non-diagnostic.
- Goal urine volume for stone prevention is ≥2.5 L/day; cystine stone formers often require ≥4 L/day.
- Thiazide diuretics are indicated for hypercalciuria + recurrent calcium stones; potassium citrate is indicated for hypocitraturia + recurrent calcium stones.
- Potassium citrate is first-line therapy for uric acid stones (alkalinize urine pH >5.5, but avoid >7.0 to prevent calcium phosphate stones).
- Stone compositions most resistant to SWL (descending): cystine > calcium phosphate (brushite) > calcium oxalate monohydrate > matrix.
- Contraindications to SWL include obstruction distal to stone, pregnancy, uncorrected coagulopathy, untreated UTI, arterial aneurysm near stone, and inability to target stone.
- Factors negatively affecting SWL success: skin-to-stone distance >10 cm, stone attenuation ≥1000 HU, resistant stone composition, unfavorable lower pole anatomy.
- Hemorrhage is the most significant complication of PCNL; management sequence: nephrostomy tube → clamp tube → Kaye tamponade balloon → angioembolization → partial nephrectomy.
- Delayed bleeding after PCNL is most commonly due to AV fistula or pseudoaneurysm and is treated with selective renal arteriogram + transcatheter embolization.
- AUA: Uncomplicated ureteral stones <10 mm should be offered observation ± MET with α-blockers (recommended for distal; option for mid/proximal).
- URS is first-line for distal and mid ureteral stones; URS and SWL are both options for proximal ureteral stones.
- Asymptomatic non-obstructing caliceal stones may be observed; ~50% progress, ~10-20% require surgical intervention at 3-4 years.
- Lower pole stones >10 mm: PCNL preferred over URS; SWL not recommended. Stone burden >20 mm: PCNL first-line.
- First-time stone formers have ~50% risk of recurrence within 10 years.
- In pregnancy, observation is first-line; 50-80% of pregnant patients pass stones spontaneously. NSAIDs are contraindicated.
- Bladder outlet obstruction is the most common cause of secondary bladder calculi in adults; stones are usually uric acid (sterile urine) or struvite (infected urine).