7. Types of Urolithiasis Based on
Stone Composition
(Dorit E. Zilberman, Michael N. Ferrandino,
and Glenn M. Preminger)
8. Calcium Stones
• Stones with calcium
components develop as a
result of the greatest
variety of metabolic
disorders and often patients
present with a
combination of stone
forming risk factors.
Stone Composition & Possible
Clinical Associations
9. Uric Acid Stones
• Patients with pure uric acid urolithiasis generally have a
low urinary pH (<5.5) and are therefore defined as having
gouty diathesis.
Infection Stones
• High urinary pH (>7.5) is associated with infection. Urea
splitting organisms leads to an increase in the ammonia
concentration, which promotes infection stone formation,
which compose the majority of stag-horn calculi.
10. Cystine-Based
Stones
• Cystine urolithiasis is the result of an autosomal recessive
trait, which disrupts the transepithelial transport of cystine,
ornithine, lysine, and arginine. The concentration of cystine
rises to levels above the saturation point, leading to
precepitation of cystine crystals.
• Even though cystine stone formers all have definitive
genetic disorders, they have been found to have a number
of other metabolic risk factors, which can contribute to
their stone formation
11. Metabolic Evaluation
of Stone Disease
Why?
• The main goal of metabolic evaluation is to prevent recurrent
stone formation in high-risk stone producers, as well as
to prevent further growth of any existing stones.
12. Metabolic Evaluation
of Stone Disease
Who?
1. Patient with stone who wishes to undergo metabolic
evaluation
2. Single stone with risk factors:
a. Family history
b. Intestinal disease
c. Chronic diarrhea
d. UTI
e. Gouty
f. Osteoporosis
g. Skeletal fractures
3. Recurrent stone formers
4. Children
5. Controversial: uric acid/struvite/cystine stones
13. Metabolic Evaluation
of Stone Disease
When?
• Many authors suggest that one should wait at least 1 month
after stone passage or stone removal, allowing the patient to
return to their normal routine, otherwise the metabolic
evluation may yield unhelpful information.
14. Metabolic Evaluation
of Stone Disease
How?
• History & Examination
• Stone Analysis
• Serum Chemistry
• Urine Culture
• Urinalysis
• 24 hour urine collection
• Radiological Imaging
15. Metabolic Work-up of
Stone Disease
• The basic metabolic evaluation begins with a thorough
history and physical exam, (similar previous conditions or
family history)
• Stone Analysis: For patients with less common stone
compositions – cystine, pure struvite, and pure uric acid –
treatment regimens could begin immediately.
• Patients with calcium phosphate stones are known to be
at increased risk from renal tubular acidosis and primary
hyperparathyroidism, while patients with calcium oxalate
stone formation have a mixture of metabolic diagnoses.
16. Metabolic Work-up of
Stone Disease
• Serum chemistry consists of basic metabolic panel (e.g.,
sodium, potassium, chloride, carbon dioxide, blood urea
nitrogen, creatinine) as well as calcium and uric acid.
• Hypercalcemia may be indicative of hyperparathyroidism
and would warrant further evaluation with a parathyroid
hormone assay. The presence of hypokalemia and hyper-
chloremia is strongly suggestive of metabolic acidosis
17. Metabolic Work-up of
Stone Disease
• Urine Cultures positive for Klebsiella, Proteus,
Pseudomonas, or other urea-splitting organisms may indicate
the presence of struvite stone
• Urine Analysis with PH between 6.8 and 7.2 suggestive of
RTA, a pH greater than 7.5 correlated with urinary tract
infection whereas a pH less than 5.5 defines the diagnosis of
gouty diathesis.
18. Metabolic Work-up of
Stone Disease
• 24 hour collection of urine to measure: total volume, pH,
calcium, phosphorus, oxalate, citrate, sodium, magnesium,
potassium, uric acid, and sulfate.
• It is our routine to have the patient collect two 24 h urine
samples on two different days (either consecutive or
separate) with the patient on their “normal routine”
(normal diet, fluid intake, medications, physical exercise,
etc) .
19. Metabolic Work-up of
Stone Disease
• Many Authors consider radiologic imaging as a part of the
basic metabolic evaluation, as there are insights which
can be gleaned from the different imaging techniques.
• For example, multiple researchers have reported the use
of CT to ascertain stone composition based on
measurement of Hounsfield units
