What do we do when we want to clinically
evaluate that patient and when do we do it?
The first symptomatic kidney stone
does warrant a basic evaluation.
So there's a number of things that we
want to do during this basic evaluation,
number one: we want a good stone history.
That means we want to know the number
of stones people have had in the past,
the frequency with which they've had them,
the age of first onset - were
they younger, were they older?
the size of the stone and the type
of the stone if they know what that is,
and the need perhaps for urological intervention
meaning that a urologist would need to come in
and break that stone up or retrieve the stone, or
whether or not they've had stones in association with UTI.
Medical history is also important.
Maybe that patient has an underlying
condition that would predispose them to a stone,
for example there are conditions that cause
hypercalcemia for calcium-based stones
or hypercalciuria, that means
too much calcium in the urine
These are things like hyperparathyroidism,
sarcoidosis or malignancies.
We'd want to know if our patient has a
history of gout because that would be very critical
in determining whether or not
the patient has uric acid stones.
Medications will also be very important.
Calcium-based stones are often
associated with something like loop diuretics.
Remember these work at that thick
ascending limb of the loop of Henle
and that's where we have paracellular calcium
absorption when we're using a loop diuretic
that will increase calciuria or calcium in the urine
and potentially can increase stone precipitation.
High doses of vitamin D,
remember the action of vitamin D?
it causes intestinal absorption of calcium.
If our patients are on super-therapeutic
doses, they can be absorbing too much calcium.
Also patients taking exorbitant calcium
supplements or antacids can also be at risk
and then medications like topiramate
which is an anti-epileptic drug.
Uric acid-associated stones are associated
with salicylate, probenecid, melamine
which we don't see but has been
associated with contaminated infant formula.
Medications that precipitate into
stones include things like triamterene.
Remember that's that potassium-sparing
diuretic, oftentimes used with hydrochlorothiazide.
Acyclovir and these are usually
parenteral or intravenous high doses
and then our Proteus inhibitors for ART and our
HIV population which include indinavir and nelfinavir.
Occupation is also very important.
If our patients have vigorous physical
activity without adequate hydration,
for example working outside in high temperatures or
in occupation that requires minimizing bathroom breaks
and I think we as medical professionals are very
guilty of that particular people who are working in the OR.
They oftentimes limit the amount that they're
drinking so they don't have to interrupt their cases.
Diet intake is also important.
Patients who are taking high sodium
diets, high animal protein or oxalate,
purines in sugar-sweetened drinks
all predispose to stone formation.
If you look at our table here, for
patients who make oxalate stones,
there's actually quite a few different
foods that can predispose to these stones
and some of our favorites
might be in here like black tea.
That's what our patient was drinking.
Chocolate, I think a favourite of almost everybody and
then some of the leafy greens which we may not expect.
Looking at some of the high purine
foods would be things like fish, meat.
Organ meats in particular - liver,
kidney tends to have a lot of purines in it
and then surprisingly, some of our vegetables
like the asparagus and cauliflower will as well.
Something to note is that calcium
intake should be adequate.
So patients who minimize calcium can actually lead
to bone demineralization and worsens stone burden
because they are resorbing
bone liberating it into the circulation.
And then finally, fluid intake and particularly what we're
looking for are people who are minimizing the fluid intake.
Physical exam can also hold some important clues
for us, we want to look for evidence of systemic disease.
Remember our patient?
he had tophaceous gout.
When we see something like that, that should be an
automatic association thinking about uric acid stones.
Urine studies are gonna be critical.
We want to look on the urine analysis for the pH.
Do they have a high or an alkaline pH,
meaning that that pH is greater than 6.5?
We're gonna be thinking about certain stones
that are gonna precipitate in that environment
so things like calcium phosphate or struvite stones.
How about patients with lower pH?
So if you have a lower pH, so a pH of
less than 5.5, then we think about things like
uric acid stone formation,
calcium oxalate stones.
I do want you to pay attention to that
because that's a very popular board question.
Urine culture is also gonna be important because struvite stones
are in particularly associated with urease-producing bacteria.
Hematuria can also be seen on
that urine analysis as we talked about.
This indicates active stone or crystal passage.
And then finally specific gravity might be important.
A very high specific gravity might be a clue
that your patient has inadequate hydration.
Some of the other things that
urine studies show are crystals.
So in particular what I've got shown here
in the first image is calcium oxalate stones
and if you look on their microscopy, you'll see these
beautiful crystals, they almost look like an envelope.
We can also see struvite crystals in the
urine and these often appear as coffin lids
and that's how they've been described.
We also want to get serological or blood work as well.
We want a look at our patient's
serum electrolytes, their creatinine,
their calcium and phosphorus and uric acid
-these are all things that would help us with clues
in terms of what is going on
with their underlying condition.
If we're concerned for example of hypercalcemia or high
calcium levels, we want to get a serum parathyroid level.
Stone analyses are very helpful so if you have a
retrieved stone either from your urological intervention
or a patient is passing stones and oftentimes they will
bring a stone right into your office after they've passed it,
that's really critical to get that stone to
your pathologist to do a chemical analysis.
Imaging is also important when it comes
to our basic evaluation of stone workup.
So at the very least, you can
get it abdominal radiograph.
Abdominal radiographs will show
radio-opaque stones but I want you to remember,
it's not gonna show all stones
because uric acid stones are radiolucent.
The pros or the advantages of getting an
abdominal radiograph is that it's inexpensive,
it's available maybe all settings.
The cons, the disadvantages are that it
doesn't detect radiolucent stones like uric acid
and it's radiation, we can't use it during pregnancy.
So the image on the right here is an abdominal
radiograph and what you can see our two arrows pointing to
is that this patient has a radioopaque
densities, these are stones in both of his kidneys.
So another imaging modality and
probably what people do most commonly
is a non-contrast CT of the
abdomen and pelvis, without contrast.
These stones here are going to appear as bright densities.
Advantages of doing this?
very high sensitivity and specificity for
detecting ureteral stones and obstruction.
It's rapid, you can do it relatively quickly.
The disadvantages to doing this is that we're really
exposing our patients to a fairly high dose of radiation.
And we certainly can't use it during pregnancy.
So this is an image on the right that shows an
axial section of the CT scan taken through the kidneys,
and what you can notice here is
that this patient has hyperdensities,
so bright densities seen in both the right and
left kidney, and these are consistent with stones.
Now a third imaging modality
that we may do is an ultrasound.
An ultrasound will show stones as
an echogenic focus or a bright focus.
Advantages of doing an ultrasound,
it does have a high specificity
meaning that if we see
the stone, we know it's there
There is no radiation exposure and
we can use it during pregnancy as well.
Disadvantages - sensitivity is not as
high as CT so if we don't see a stone,
it doesn't necessarily rule
out that the patient has a stone.
So that's our basic evaluation.
What about a complete evaluation?
Who needs a complete evaluation?
There's certain populations
that we really need to think about.
Any child who presents with stones
will need a complete evaluation.
Non-calcium stones like our patient with the
uric acid stones will need a complete evaluation
and people who have had multiple recurrent stones
that have been particularly increasing in size and number
absolutely will need a complete evaluation.
What is the complete evaluation?pp
It's a 24-hour urine collection that will include:
volume, phosphorus content, urinary
calcium, uric acid, oxalate and citrate.