150

Practical Urology: EssEntial PrinciPlEs and PracticE

collections while a patient is obstructed,infected,

hyperuricemia. Hypercalcemia may be indica-

or suffering from renal colic yields unhelpful

tive of hyperparathyroidism and would warrant

information.

further evaluation with a parathyroid hormone

assay. The presence of hypokalemia and hyper-

Metabolic Workup for Stone Producers

chloremia is strongly suggestive of metabolic

acidosis and is highly associated with distal

Medical History and Physical Examination

renal tubular acidosis. Finally, if clinical history

suggests possible derangement of purine metab-

The basic metabolic evaluation begins as any

olism serum uric acid may be confirmatory.

physician–patient interaction should, with a

thorough history and physical exam. Key points

Urine Evaluation

in the history should include: medical illnesses

Urine Cultures

and surgical procedures, which may contribute

to stone formation, family history of nephro-

Urine cultures are valuable if the patient dem-

lithiasis, evaluation of medications and dietary

onstrates

signs and

symptoms

of infection.

supplements,as well as dietary habits.Evaluation

Cultures

positive for

Klebsiella

pneumonia,

of general hydration and activity levels are

Proteus mirabilis, Pseudomonas aeruginosa, or

important to consider.

other urea-splitting organisms may indicate the

presence of struvite stone. Additionally, clinical

Stone Analysis

and surgical management will vary depending

The ability to analyze urinary stones is an inte-

upon the presence or absence of infection.

gral part of the metabolic evaluation. The most

Urinalysis

common outcome of an acute stone episode is

spontaneous passage and patients do not

Urinalysis should include pH and a review of

always collect these stones for future chemical

urinary sediment, as these results may provide a

analysis.

clue to stone composition. A variation in pH

The operating theater is the most reliable

may point to particular diagnoses, with a

venue for stone collection. Despite the fact that

pH between 6.8 and 7.2 suggestive of RTA, a pH

stones or fragments are not always collected,

greater than 7.5 correlated with urinary tract

valuable information can be gained from analy-

infection whereas a pH less than 5.5 defines the

sis of stone composition. In fact, a further sim-

diagnosis of gouty diathesis. Care should be

plification of the metabolic evaluation has been

taken, however, not to rely too heavily on a sin-

proposed based on stone composition.25

gle urine pH as the patient’s dietary may be

For patients with less common stone com-

reflected instead of the underlying metabolic

positions – cystine, pure struvite, and pure uric

disorders.29

acid – minimal to no further evaluation was

required and treatment regimens could begin

immediately.25,27,28 Patients with calcium phos-

Twenty-Four Hour Urine Collections

phate stones are known to be at increased risk

The urine constituents most commonly assayed

from renal tubular acidosis and primary hyper-

parathyroidism, while patients with calcium

include: total volume, pH, calcium, phosphorus,

oxalate stone formation have a mixture of meta-

oxalate, citrate, sodium, magnesium, potassium,

bolic diagnoses.

uric acid, and sulfate. Whereas most of these

parameters are self-evident, sulfate is added to

Serum Chemistry

the list to assess the volume of animal protein

ingested, which may increase the risk of certain

Serum chemistry consists of basic metabolic

stones. Creatinine is measured to evaluate the

panel (e.g., sodium, potassium, chloride, carbon

adequacy of urine collection. Values lower than

dioxide, blood urea nitrogen, creatinine) as well

500 mg/day should rather be considered as

as calcium and uric acid.This blood panel should

either incomplete collection or dilution with

be performed in an attempt to identify hypercal-

fluid whereas creatinine values >3,000 mg/day

cemia, hypokalemia, metabolic acidosis, and

in normal-sized individuals suggest an “over