Transcript Schilling I, II, and III - PPT

Non Imaging In Vivo
Urine Test For Evaluation of
B12 Absorption
Vitamin
12
B
• B12 is essential for normal RBC production in bone
marrow and normal liver cell metabolism.
• Vitamin B12 is not produced by plants or animals.
• It is actually produced by microorganisms found in soil
and intestines and rumens (large first part of the stomach)
of animals.
• Dietary B12 can naturally be found in animal foods including
fish, milk and milk products, eggs, meat, and poultry.
• Fortified breakfast cereals are an excellent source of vitamin
B12 and a particularly valuable source for vegetarians
Uncommon to Be
12
B
Deficient
• Diets of most adult Americans provide recommended
intakes of vitamin B12, but deficiency may still occur as a
result of an inability to absorb B12 from food.
• It can also occur in individuals with dietary patterns that exclude
animal or fortified foods.
• As a general rule, most individuals who develop a vitamin
B12 deficiency have an underlying stomach or intestinal
disorder that limits the absorption of vitamin B12.
• Sometimes the only symptom of these intestinal disorders is
anemia resulting from B12 deficiency.
Symptoms of
12
B
Deficiency
• Characteristic signs of
• Deficiency also can
B12 deficiency include:
lead to neurological
changes such as:
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Fatigue
Weakness
Nausea
Constipation
Flatulence (gas)
Loss of appetite
Weight loss
• Numbness and tingling
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in the hands and feet
Difficulty in
maintaining balance
Depression
Confusion
Poor memory
Soreness of the mouth
or tongue.
12
B —The
Short Story
• Vitamin B12, also called cyanocobalamin, is
important to good health.
• It helps maintain healthy nerve cells and red blood cells,
and is also needed to make DNA, the genetic material in
all cells.
• Vitamin B12 is bound to the protein in food.
Hydrochloric acid in the stomach releases B12 from
protein during digestion. Once released, B12
combines with a substance called intrinsic factor
(IF) before it is absorbed into the bloodstream.
Absorption of
12
B
• For the body to absorb B12, it must be complexed
with intrinsic factor (IF).
• IF is a protein secreted by parietal cells of the gastric
fundus.
• The complex binds to receptors in terminal ileum in
the presence of an alkaline pH and calcium, where
B12 is actively transported across the mucosa.
• As B12 enters the portal vein of the liver, it binds to
transcobalamin II, a transport protein.
• Then it is delivered to the liver.
Absorption of
12
B
Continued
• Over the next 8-12 hours, portions of this B12
reenters circulation binding to a larger transport
protein, transcobalamin I.
• When the storage capacity of transcobalamin I is
exceeded, B12 is excreted by the kidneys into the
urine via glomerular filtration.
• As in, when we administer a flushing dose of B12, which
we will discuss later.
• This is the basis of the test.
1
2
Parietal cells
of the gastric
fundus secrete
Intrinsic
Factor which
binds to B12
B12 is Ingested
5
4
B12 enters portal
vein and binds to
Transcobalamin
II and then
enters the liver
B12 re-enters
circulation binding
to transcobalamin I
3
IF/B12
complex binds
to receptors in
terminal ileum
and the B12 is
actively
transported
across mucosa
6
All B12 not bound to
transcobalamin I is
excreted out via kidneys
and bladder
Storage of
12
B
• B12 is primarily stored in the liver (a storage
depot).
• Total body stores are high while daily excretion is
low.
• This is why it takes 3-5 years to develop B12 deficiency
if dietary intake is halted or malabsorption occurs.
• Thus B12 deficiency due to diet is rare, occurring in
strict vegetarians.
12
B
Deficiency Causes
• Inadequate Intake (rare)
• Malabsorption
• Absence of IF (pernicious anemia)
• Gastrectomy
• Excess HCI (Zollinger-Ellison Syndrome)
• Intestinal Absorption Problems
• Destruction, removal or invasion of ileal absorption sites
• Competition for B12 (tapeworm, bacterial overgrowth in
small bowel lesions)
12
B
Deficiency Causes Continued
• Pancreatic disease
• Chronic Pancreatitis
• Cystic Fibrosis
• Causes failure of the pancreas to produce enzymes
involved in breakdown of fats and their absorption from
the intestine
• Medications
• p-aminosalicylic acid, Neomycin, colchicine,
Prilosec, calcium-chelating agents
• Genetic abnormality in transport proteins
12
B
Deficiency Effects
• Megoblastic anemia
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• Occurrence of large primitive red cell
Thrombocytopenia
• A reduction in the number of platelets
Leukopenia
• Reduction in the number of white blood cells
Degeneration of the spinal cord
Death
• Only if side effects cannot be reversed
Note that hematological change is reversible, neurological may not be.
Primary Reason for Absorption Test
• Pernicious anemia is a type of anemia caused by the
body’s failure to absorb vitamin B12.
• Pernicious anemia is the most common cause of vitamin
B12 deficiency.
• Pernicious anemia is characterized by the presence
of anti-parietal cell and anti-intrinsic factor
antibodies (50-80%) leading to intrinsic factor
deficiency and gastric mucosal atrophy.
Indications for Schilling Test
• Low serum B12, with or without neurological or
hematological symptoms.
• 2/3 of patients with low serum B12 have no signs or no symptoms
• Confirm the diagnosis of B12 malabsorption and determine
the mechanism.
• Hematological changes with non-diagnostic serum tests.
• Detect patients at risk for B12 deficiency (e.g. post
gastrectomy, ileal disease, family history of pernicious
anemia).
Isotopes Used in Schilling’s Test
• Cobalt 57
• 122 keV, half life of 270 days
• Cobalt 58
• 810 keV, half life of 71 days
• Cobalt 60
• 1170 keV, 1330 keV, half life 5.2 years
• Cobalt 57 is isotope of choice, why?
Why Cobalt?
• The reason that cobalt is used as the
radiopharmaceutical is because Vitamin B12
(cyanocobalamin) has a non-radioactive
form of cobalt as its central metal atom.
• Radioactive Cobalt can be substituted for
the cold atom, producing a tagged form of
B12.
Pre-Test Concerns
Confirm B12/Folate levels have been drawn and
that the patient has a low B12.
•A normal B12 level virtually excludes B12 deficiency.
•If absorption test is done prior to B12/Folate levels, labs
checking for levels of B12 will not give true values. This is
because B12 is administered in the Schilling Test.
•Folate deficiency can cause a megaloblastic anemia
exactly the same as B12 deficiency except neurologic
symptoms do not occur.
More Pretest Concerns
–Ensure overnight fasting.
• The vitamin B12 from a meal can affect absorption
(decrease it) leading to a false positive test.
–Confirm that no parenteral vitamin B12 has been
given within the last three days.
• Enterohepatic circulation will compete with B12
absorption from the ileum.
Stage I B12 Absorption Test Technique
• Patient should be NPO for 12 hours
• Have patient void, administer 0.5 uCi of C0-57 labeled
Vitamin B12 in a 0.5 ug Vitamin B12 capsule--orally.
• Up to 2 hours later, administer a flushing dose of 1,000 ug
of “cold” Vitamin B12 intramuscularly or subcutaneously.
• This is to saturate transport proteins and ensures any radioactive
B12 absorbed into the blood from the gut finds normal binding sites
saturated and will be excreted via glomelular filtration into the
urine sample.
Stage I Technique Continued
• Collect and pool urine for 24 hours.
• 48 hours if there is renal impairment
• Maximum excretion is 8-12 hours after administration
• Co-57 labeled B12 absorbed thru GI tract will not be
bound by saturated transport proteins and will thus
be excreted in the urine.
• Measure volume for 24 hour urine collection
Stage I Technique Continued
• Prepare standard
• Dilute 0.5 ml of Cobaltous Chloride Co-57
provided with kit, with 3.5 ml of water.
• Standard solution contains the equivalent of 1%
of the total radioactivity in the oral dose.
• Pipette and count 4 ml aliquots of urine and
dose standards for 10 minutes.
• Calculate percent administered dose
excreted over (each) 24 hour period.
Calculations
•Calculate the percent urine excretion of labeled B12 as
follows:
(Avg.urine cpm – Bkg cpm) x (Total urine vol. /counting volume) x 100
--------------------------------------------------------------------------------------(Std. cpm – Bkg cpm) x Dilution Factor
• Dilution Factor is equal to 100, if the standard is a 1% of the dose.
• Example: original concentration is 100% and the prepared standard
is 1%
• 100/1 = 100
Results of Stage I
• Normal
• Greater than 10% of dose excreted in 24 hours
• Borderline
• 6-10% of dose excreted in 24 hours
• Abnormal
• Less than 6% of dose excreted in 24 hours
• Normally for pernicious anemia the result is 1-3%
Stage II Schilling Test
• If the Stage I test is abnormal, the exam is
repeated by administering 0.5 ug of Co57
labeled with Vitamin B12 complexed to
human intrinsic factor.
Stage II Results
• Normal results indicate pernicious anemia
• No change in results indicates malabsorption instead
of lack of IF
• Chronic B12 deficiency from PA can produce
atrophy of ileal mucosa. This causes a decrease in
intestinal absorption of B12.
• In these cases, there may be only a minor correction in
Stage II.
• To diagnose this, repeat Stage II several weeks/months
after institution of B12 therapy to allow mucosa to
recover. (Stage III Absorption Test)
Current Available Method—
Rubratope Diagnostic Kit
• Available through Squibb
False Positive Results
• False positive results may occur in patients with
diminished renal function or obstruction.
• In patients with extremely poor renal function, 3-day
collection should be performed.
• When the patient has multiple containers, the
following should be done:
• Percent excreted in second 24 hour sample should be
added to first.
• If combined excretion is in the normal range, test is
interpreted as normal.
False Positive Results
• False Positive results can occur if a portion
of the urine volume was lost.
• To verify all urine was collected
• check urine creatinine level
• Should be greater than 15 mg/kg/day.
• compare differences in volume between 24
hour and 48 hour collections.
False Positive Results
• Megoblastic anemia secondary to folate
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deficiency
Veganism
Third Trimester Pregnancy
Contraceptives and anti-convulescents
Multiple myeloma
Radioactivity present in the urine prior to
exam.
False Positives
• The following drugs, can result in
malabsorption of vitamin B12:
• Most antibiotics, methotextrate, pyrimethamine,
colchicine, para-aminosalicyclic acid, or
excessive alcohol intake for longer than two
weeks.
False Normal Results
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Recent parental Vitamin B12
Nitrous oxide inhalation
Severe liver disease
Chronic granulocytic leukemia
Elderly patient
H2 Blockers and iron deficiency anemia which
lead to decreased gastric pH
• Fecal contamination
Other Methods for Determining
B12 Deficiency
• Instead of urine, an
absorption test can be done
by obtaining a stool sample
72 hours post isotope
ingestion and count sample
in a well counter. This
expresses B12 not absorbed.
Defective absorption is the
problem if more than 70%
of isotope is excreted
fecally.
• There is also a plasma
Schilling Test. 8-10 hours
after oral dose, draw 20 ml
of blood and centrifuge.
Draw plasma off of blood
sample and count along
with standard. Normal is
.25 - 2.5%. This test is
good due to the fact it is
very little patient
dependant.
An In-depth Review…
Deficiency leads to production of
abnormal, large red cells
• Vitamin B12 is a precursor of DNA synthesis. Lack of B12
impairs DNA synthesis within a cell, but, RNA and protein
synthesis are unaffected.
• This results in dissociation between nuclear and cytoplasmic
maturation, producing cells which have enlarged mature
cytoplasm and immature nucleus (megaloblastosis).
• These findings are most prominent in cells with rapid
turnovers--blood and GI tract. Thus, why B12 deficiency can
lead to hematological changes--megaloblastic anemia or
megaloblastic changes in the GI tract.
• If these megaloblastic changes occur in the terminal ileum,
vitamin B12 absorption is inhibited.
B12 Deficiency Causes Neurological
Changes
• Vitamin B12 is also required for myelin
metabolism; therefore deficiency can cause
neurological symptoms, classically involving the
posterior columns and peripheral nerves leading to
loss of position and vibratory sensation as well as
degeneration of the spinal cord.
Absorption Overview
• Ingested B12 is released from protein by digestive enzymes
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(gastric acid and pepsin).
B12 binds to R protein in the stomach.
• R protein is found in gastric, biliary and salivary
secretions.
Pancreatic enzymes degrade B12-R and facilitate binding of
B12 to Intrinsic factor, which occurs in the presence of an
alkaline pH.
B12-IF is absorbed by the terminal ileum.
B12 enters serum bound to Transcobalamin-I and
Transcobalamin-II.
Conclusion
• Diagnosing B12 deficiency is imperative for patient’s
long term recovery.
• The Rubratope Kit is easy, cost efficient, and give a
direct evaluation of body’s ability to absorb B12.
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