kidney stone causes, evaluation and prevention

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Kidney Stone Causes, Evaluation and Prevention

Dr. Britton Edgett Tisdale, MD, Urologist Assistant Professor of UrologyState University of New York at Buffalo

Dr. Britton Edgett Tisdale, MDUBMD UrologyAssistant Professor of Urology, State University of New York at Buffalo

Male Genitourinary Reconstruction, Female Genitourinary Reconstruction, Urogynecology, Pelvic Prolapse Management Incontinence, Voiding Dysfunction Neurourology, Laparoscopic and General Urology

Offices:4233 Maple Road, Amherst, NY, Phone: (716) 725-62771020 Youngs Rd, #110, Williamsville, NY Phone:(716) 725-62772816 Pleasant Avenue, Hamburg, NY Phone (716) 725-6277

Surgical and Inpatient Services:Millard Fillmore Suburban HospitalBuffalo General HospitalErie County Medical Center

Objectives

1. Why do we make kidney stones2. Evaluation of those that have recurrent

kidney stones3. Prevention of kidney stones

Keep in mind, this is the basics only, not a comprehensive review

What are kidney stones made of?

Composition Male Female All

Calcium OxalatesCalcium PhosphatesUric Acid & UratesStruviteCystineOthers

73.24.7

17.41.61

2.1

62.914.410.35.02.54.9

70.17.615.22.81.54.8

Dr. Britton E. Tisdale, MD, Urologist 716-725-6277 ubmdurology.com/contact/

Why do stones form, in general?

1. Not enough of things that prevent stones.

2. Too much of things that cause stones


Why do stones form in general?

Not enough of things that prevent stones1.Not enough fluid intake causes low urine volume

Low urine volume is often seen in 24 hour urine collections in stone formers

Need to drink enough to make 1.5 – 2.0 liters/quarts of urine per day

Dilutes things in the urine that cause stones.

2.Not enough citrate, magnesium, potassium, etc.


Why do stones form in general?

Too much of things that cause stones in the urine Too much acid Too much calcium Too much oxalate Too much sodium Too much uric acid


Why do calcium stones form?

Too much calcium in the urine = Hypercalciuria Idiopathic = we don’t know why

• 50% of calcium stones Intestinal issue = absorptive hypercalciuria

• High intestinal calcium absorption, more than one cause Bone issue = resorptive hypercalciuria

• Increased bone resorption putting more calcium in blood Kidney issue

• Not reabsorbing calcium during urine production



Too much calcium in the urine = Hypercalciuria1.Parathyroid gland problem = Primary Hyperparathyroidism

5% of calcium stones Inherited syndrome

2.Too much vitamin D Taking too much Producing too much: sarcoidosis

3.Too much calcium intake/absorption (or not enough intake)4.Too much thyroid hormone5.Too much sodium intake



Hypocitraturia =Not enough citrate in the urine1.Normal Excretion is 300 - 900mg/day, (> 1.2 mmol/day)2.Citrate binds calcium in the urine, preventing stone formation3.Lower in High Protein Diets


Why do oxalate stones form?

Too much oxalate in the urine = hyperoxaluria1.Too much oxalate intake2.Not enough calcium intake with meals3.Too much absorption from intestines

Inflammatory bowel disease Gastric bypass surgery

4.Not enough pyridoxine (B6) intake5.Specific genetic mutations affecting oxalate metabolism


Calcium Oxalate crystals and stone


Why do uric acid stones form?

Hyperuricosuria = too much uric acid in the urine1.Low/acid pH in urine decreases solubility2.Solubility not high in the first place, is ~90mg/L3.Normal excretion 5-600mg/day = 4-4.5 mmol/day

Intake of certain foods can increase Some medications can increase Medical conditions can increase

4.Low urine volume


Uric Acid crystals can cause Calcium Oxalate Stones

Small uric acid cystals are a nidus for calcium oxalate stone formation

Bind Calcium Oxalate Promote Crystal Growth


Uric Acid


Struvite Stones = “Infection Stones”

1. Ammonium magnesium phosphate stones form in infected urine

2. pH is High [> 7] 3. Bacterial Urease

urea ammonia ammonium

4. Proteus, Klebsiella, Pseudomonas, many others


Struvite Stones


Other Stones

1. Calcium phosphate2. Cystine

Genetic “COLA” abnormality

3. Drug Stones triamterene Indinavir Many others

4. Xanthine

Ciprofloxacin

Indinavir


Renal Tubular Acidosis

1. Distal RTA (Type 1) Defective Excretion & Retention of

Hydrogen Ions in Urine Problem with excretion, problem with

trapping Calcium phosphate stones Nephrocalcinosis Non-anion gap metabolic acidosis Relatively alkaline urine pH


Evaluation of stone formers

What to Measure1.24 Hour Urine Collection

2.Blood tests

3.Imaging



24 Hour Urine Collection Things that cause stones

calcium, phosphate, uric acid, oxalate, sodium Things that prevent stones

citrate, magnesium, potassiuim Other things

Volume, creatinine, pH



Blood tests BMP Ionizied Calcium & PTH Vitamin D TSH


Evaluation of stone formersImaging Studies to evaluate stone size, number, location

Non-contrast CT of the abdomen and pelvis >/= 95% sensitivity and specificity

Ultrasound + Xray of kidneys + ureters + bladder = “KUB”

50% sensitive for small stones

Intravenous pyelogram = “IVP” – can be done, but mostly historical


Prevention of Calcium Oxalate Stones

1. Dietary and Fluid Intake Modification

2. Medications


Prevention of Calcium Oxalate Stones

Dietary Modification Fluid Intake Animal Protein Intake Sodium Intake Calcium Intake

Not what you might think Oxalate Intake


Prevention of Calcium Stones

Medications Hydrochlorthiazide

Reduce calcium in the urine Phosphates

Bind calcium in the intestines Potassium Citrate

CaOx, RTA (CaP), Uric acid, Cystine


Prevention of oxalate stones

1. Calcium taken with meals binds oxalate in the gut from food

2. Cholestyramine3. Pyridoxine4. Magnesium

magnesium oxalate is soluble


Prevention of Uric Acid Stones

1. Drink more water2. Restrict dietary purines3. Medications

Allopurinol• prevents formation of uric acid

Alkalinize the urine


Prevention for other types of stones

1. Drink more water2. Medications

Antibiotics for struvite/“infection” stones Penicillamine for cystine stones Other medications

3. Stop medications that may be causing stone formation.


Take Home Messages1. Kidney stones are common (10% lifetime

risk in North America)

2. Kidney stone formation & growth can be prevented or slowed to reduce the frequency of need for surgical intervention


Take Home Messages

Prevention of Kidney Stone Formation & Growth

Increase urine volume by drinking more water Avoid excess dietary sodium and animal protein “Normal” Calcium (1 - 1.5 g/day) intake with

meals (not low or high intake) Potassium Citrate

CaOx, RTA (CaP), UA, Cystine


Scenario: Calcium Oxalate Stones60 year old male

2 episodes of renal colic from ureteral stones Calcium oxalate stones Blood tests - normal Non-contrast CT/CAT scan: no more stones

BEFORE looking at the next slide, what other test(s) would you order?


Urine Chemistry from 24 hour urine collection

1. Volume 1.75 L2. Calcium 2.9 mmol/day (N 2.5 - 7.5 mmol/d)3. Oxalate 270 mol/day (N < 450 mol/day)4. Urate 5.5 mmol/day (N < 4.5 mmol/day)5. Citrate 0.6 mmol/day (N > 1.2 mmol/day)

BEFORE looking at the next slide, what treatment/prevention measures would you order?


Prevention of Calcium Oxalate Kidney Stones

1. Drink more fluid = water 2. Avoid excess intake of sodium/salt, oxalate3. “Normal” animal protein/meat intake

No more than 3 “deck of card” sizes per day

4. “Normal” calcium intake, with meals5. Take in more citrate (diet or prescription)6. Medications

Consider hydrochlorothiazide, chlorthalidone Consider allopurinol (high urine uric acid also can help cause

calcium oxalate stones)


kidney stone causes, evaluation and prevention

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