Kidney stones Flashcards
How does supersaturation lead to kidney stone formation?
Once concentration of an ion exceeds solubility threshold, it begins to precipitate into a stone
What is the most common type of kidney stone?
Calcium-containing stones (calcium-oxalate, calcium phosphate)
What are two risk factors for calcium-containing kidney stones?
Hypercalcuria and/or hyperoxaluria (high oxalate foods, excessive vitamin C, malabsorptive GI conditions)
What is the composition of struvite stones?
Magnesium, ammonium, phosphate, and calcium carbonate
How do struvite stones form?
They require presence of urease-positive bacteria in the urine, which increase the pH to make phosphate insoluble such that it precipates with surrounding magnesium/ammonium/calcium
What type of kidney stone forms the majority of staghorn calculi?
Struvite (forms a large stone that penetrates more than one renal calyx)
What is the most common bacteria responsible for struvite stone formation?
Proteus
What is the driving force of uric acid stone formation?
Hyperuricosuria caused by high purine/protein diet or statesof cell turnover/breakdown
What pH do uric acid stones form at?
Acidic urine (soluble above pH of 5.5)
What is a unique characteristic of uric acid stones?
Radiolucent on x-ray imaging
How are cysteine stones formed?
Due to inherited disorders of metabolism (very rare)
What are 4 general risk factors for kidney stone formation?
- low urine volume (increases concentration of solutes)
- high sodium diet (leads to decreased calcium reabsorption and thus increased urinary calcium/calcium precipitation)
- high protein diet (increased acid load, buffered by release of Ca from bone reservoirs)
- hypocitraturia (citrate inhibits stone formation)
What is the clinical presentation of kidney stones?
Acute flank pain, hematuria
What type of kidney stones are not visible on x-ray?
Uric acid stones (radiolucent)
What is the treatment for kidney stones?
pain control and fluids usually (they pass on their own), surgery may be required if they cannot pass (rare)
What are 5 general preventive strategies for preventing kidney stone formation?
- increase urine volume
- low Na diet
- avoid calcium supplements (but eat a normal amount of calcium)
- add citrate supplements
- possible thiazide diuretics to lower urinary calcium levels
A 45-yo caucasian male with a history of chronic myeloid leukemia for which he is receiving chemotherapy presents to the emergency room with oliguria and colicky left flank pain. His serum creatinine is 3.0 mg/dL and his urine pH is 5.0. You diagnose nephrolithiasis. His kidney stones, however, are not visible on abdominal x-ray. His stone is likely composed of what?
Uric acid - hyperlucent on x-ray
A 30-yo male with a history of 2 prior episodes of nephrolithiasis presents to establish care in your clinic. He would like to discuss strategies to prevent future kidney stones. He has not had any analysis done of his prior kidney stones. You order a 24-hour urine collection for Ca, Na, phosphorous, uric acid, and citrate. Before even obtaining results, which of the following would be an appropriate recommendation?
a) increase dietary sodium intake
b) increase dietary protein intake
c) lower dietary calcium intake
d) increase fluid intake to target urine volume >2 L/day
d) increase fluid intake to target urine volume >2 L/day
all others could increase stone formation
What is the shape of calcium oxalate kidney stones?
Square envelopes
What is the shape of struvite kidney stones?
Coffin lid rectangles
What is the shape of uric acid kidney stones?
Diamond/rhomboid
What is the shape of cysteine kidney stones?
Hexagonal
