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Urology In-Service/Board Review > Urolithiasis > Flashcards

Urolithiasis Flashcards

1
Q

Most common metabolic abnormality, type of stone, and cause of urolithiasis in the US:

A
  1. Metabolic abnormality: hypercalciuria
  2. Type of stone in industrialized countries: calcium oxalate
  3. Cause: dehydration
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2
Q

Calcium oxalate stones

A

Most common renal and bladder stones in adults, children, intestinal bypass, IBD, and renal failure
Most common cause = dehydration
Forms in urine with wide range of pH
Radio-opaque

Calcium oxalate monohydrate = whewellite (crystals are ovals and dumbbells)
Calcium oxalate dihydrate = weddellite (crystals are envelopes and octahedrons)

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3
Q

Calcium phosphate stones

A

More common in patients with hyperparathyroidism, RTA type 1, medullary sponge kidney, and carbonic anhydrase inhibitor use
Formed in alkaline urine
Radio-opaque
Mineral name = apatite

Crystal shape = powder like and often causes cloudy urine

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4
Q

Uric acid (urate) stones

A

Normally have normal serum and urine uric acid levels
Most common cause = dehydration
Forms in acidic urine (usually pH <6.0)
Radiolucent (can’t see)

Dissolves with urinary alkalinization

Stone shape = parallelograms, double headed arrows, some in rosettes

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5
Q

Magnesium ammonium phosphate (also called struvite or triple phosphate)

A

Most staghorn calculi are composed of struvite
Most common cause = UTI
Forms in alkaline urine
Radio-opaque
Dissolves with urinary acidification

Crystal shape = coffin lids

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6
Q

Stones that form in alkaline urine

A

Struvite
Calcium phosphate
Matrix

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7
Q

Cystine Stones

A

Cause - cystinuria (usually homozygotes)
Forms in acidic urine
Radiopaque
Dissolves with urinary alkalinization

Crystals = regular hexagons

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8
Q

Matrix Stones

A

Most common cause = UTI (Proteus)
Forms in alkaline urine
Radiolucent

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9
Q

Ammonium acid urate

A

Common causes = intestinal malabsorption, UTI, phosphate deficiency,
Radiolucent

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10
Q

Protease inhibitor stones

A

Stones from precipitated drug - Indinavir, nelfinavir
Radiolucent and not visible on non-contrast CT scan
Forms in urine with pH of 5 or less

Acidifying urine to dissolve stones not practical because of extremely low pH required

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11
Q

List of radiolucent stones

A

Uric acid (urate)
Xanthine
Matrix
Ammonium urate
Protease inhibitor stones
Silica

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12
Q

Urine chemistry abnormalities that would PROMOTE stone formation

A

Hypercalciuria
Hypocitraturia
Hyperoxaluria
Hyperuricosuria
Hypomagnesiuria
Xanthinuria

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13
Q

High sodium intake increases stone risk by:

A

Increasing urinary calcium and decreasing urinary citrate

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14
Q

Organic inhibitors of crystallization

A

Citrate - decreases calcium stone formation by complexing with calcium and lowering calcium saturation, also directly inhibits calcium crystallization

Urea - decreases uric acid stone formation by increasing the solubility of uric acid (no influence on calcium stone formation)

Others: nephrocalcin, Tamm-Horsfall protein, calgranulin, GAGs, bikunin and uropontin (a form of osteopontin)

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15
Q

Inorganic inhibitors of crystallization

A

Pyrophosphate - no way to increase this in the urine

Magnesium - increases solubility of calcium, phosphate, and oxalate

Trace elements, especially zinc

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16
Q

How UTI Increases Stone Risk

A
  1. UTI causes hypocitraturia
  2. Urease producing organisms split urinary urea into ammonia and bicarbonate, which alkalized urine and increases the risk of stones formed in alkaline urine, especially struvite
  3. UTI may decrease ureteral peristalsis
17
Q

Urease producing bacteria

A

Proteus
Klebsiella
Serratia
Staphylococcus
Morganella
Providencia
Enterobacter

18
Q

Stones often associated with UTI

A

Struvite
Matrix
Carbonate apatite
Ammonium urate

19
Q

Acidosis increases stone risk.
Acidosis causes the following changes in urinary composition:

A

Increased urine calcium
Increased urine phosphate
Decreased urine citrate

Prolonged acidosis causes bone demineralization, which increases calcium delivery to the kidney and results in hypercalciuria

20
Q

Medications that may lead to urolithiasis

A

Vitamin C - metabolized to oxalate, increases urinary oxalate

Vitamin D (high doses) - increases calcium absorption, which increases calcium to kidney

Triamterene (diuretic) - precipitates in urine and forms radiolucent stones

Protease inhibitors (Indinavir and nelfinavir) - precipitate and forms radiolucent stones

Furosemide - increases calcium excretion in urine

Acetazolamide - carbonic anhydrase inhibitor creases a renal tubular acidosis and increases risk of calcium stones.
-Can be used to prevent uric acid and cystine stones (when citrate does not adequately alkalinize urine, it can be added to increase the urine pH)

Topiramate - stones composed of calcium phosphate

Zonisamide

21
Q

Type I (distal) renal tubular acidosis

A

Impairment in hydrogen ion secretion in the distal tubule, resulting in a persistently high urine pH (> 5.5) and systemic acidosis

Plasma bicarbonate is frequently < 15 mEq/L (15 mmol/L), and hypokalemia, hypercalciuria, and decreased citrate excretion are often present

Nephrocalcinosis and nephrolithiasis are possible complications of hypercalciuria and hypocitraturia if urine is relatively alkaline

22
Q

Oral medication for urinary alkalinization

A

Citrate and bicarbonate prevent stones by correcting acidosis, increasing urinary pH and increasing urinary citrate

Oral citrate is changed to bicarb ny the liver (doesn’t actually deliver citrate to kidney)

23
Q

Most common stone compositions in patients with gout?

A

Calcium oxalate monohydrate (45%)
Uric acid (52%)

24
Q

Medical conditions that increase risk of overall stone disease

A

Obesity
HTN
Diabetes
Hyperthyroidism
Gout
RTA type I
Bone disease
Primary hyperparathyroidism
Malabsorptive GI states

25
Q

Nutritional factors associated with stone formation

A

Calcium intake below or highly above the recommended dietary allowance
High sodium intake
Low fluid intake
Low fruit and vegetable intake
High intake of animal-derived purines

26
Q

Serum studies to order in screening evaluation of stone formers

A

Electrolytes: sodium, potassium, chloride, bicarbonate
Calcium
Creatinine
Uric acid

27
Q

When to suspect primary hyperthyroidism

A

Serum calcium is high or high normal

Predominantly calcium phosphate stones

Elevated urinary calcium

If suspected, get intact PTH
- Mid-range PTH in the face of higher serum calcium (inappropriately normal PTH)
- High or high-normal PTH when vitamin D levels are low

(The diagnosis of primary hyperparathyroidism (PHPT) is usually made by finding a PTH concentration that is frankly elevated or within the normal range but inappropriately normal given the patient’s hypercalcemia)

28
Q

Calcium phosphate stone composition more likely to be associated with the following medical conditions:

A

RTA Type 1
Medullary sponge kidney
Primary hyperparathyroidism
Use of carbonic anhydrase inhibitors

29
Q

Medical Management of Kidney Stones Guidelines:
For pts with calcium stones and relatively high urinary calcium, what should they do with their diet?

A

Guideline Statement 9:
Clinicians should counsel patients with calcium stones and relatively high urinary calcium to limit sodium intake and consume 1,000-1,200 mg per day of dietary calcium

Target of <2,300 mg sodium daily

30
Q

Med Mgmt Guideline Statement 10:
Clinicians should counsel patients with calcium oxalate stones and relatively high urinary oxalate to…

A

…limit intake of oxalate rich foods and maintain normal calcium consumption

31
Q

Med Mgmt Guideline Statement 13:
Clinicians should counsel patients with cystine stones to limit…

A

…sodium and protein intake

High fluid intake is particularly important for cysteine stone formers

Need to decrease urinary cysteine concentration to below 250 mg/L

32
Q

Med Mgmt Guideline Statement 14:
Clinicians should offer ————– to patients with high or relatively high urine calcium and recurrent calcium stones

A

Thiazide diuretics
(HCTZ, chlorthalidone, indapamide)

May need to supplement potassium as these cause hypokalemia

Should still restrict sodium in the diet

33
Q

Med Mgmt Guideline Statement 15:
Clinicians should offer ———— therapy to patients with recurrent calcium stones and low or relatively low urinary citrate

A

Potassium Citrate

Potassium citrate is preferred over sodium citrate as the sodium load may increase urine calcium excretion

Sodium bicarb or sodium citrate can be considered if patient is hyperkalemic

34
Q

Med Mgmt Guideline Statement 16:
Clinicians should offer allopurinol to pat

A

Urology In-Service/Board Review (12 decks)

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