CLINICAL CHEMISTRY CHAPTER 15

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CLINICAL CHEMISTRYCHAPTER 15

• IRON
• ( TRACE ELEMENTS )

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• Introduction
• Looking and feeling a little peeked? Unusually
  pale?
• Maybe youre iron deficient. Its fairly common
  in menstruating females, anyone with GI bleeding
  and children
• The CBC will suggest iron deficiency
  Decreased HH
  with hypochromic microcytic RBCs
• But to really prove it, Iron Profiles are
  commonly ordered by physicians to document an
  actual iron deficiency
• Sometimes you get too much iron Kids loves
  all those colorful vitamins ( loaded with iron )
  An entire bottle tastes really good for a
  while, but then its off to the ER
• Hemochromatosis is a common genetic condition
  causing an accumulation of iron Should these
  people be allowed to donate blood?

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KEY TERMS

• Total Serum Iron
• Total Iron Binding Capacity
• Iron Saturation
• Transferrin
• Ferritin
• Hemosiderin
• Iron Deficiency
• Hemochromatosis
• Therapeutic Phlebotomy
• Chleation
• Fe Iron
• Ferric iron ( Fe3 )
• Ferrous iron ( Fe2 )

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• Objectives
• Define each of the Key Terms
• Discuss the main components of iron homeostasis
• Discuss the common methodologies that are used
  for the determination of iron
• Discuss the Total Iron, TIBC, Saturation and
  Ferritin concentrations associated with Iron
  Deficiency, Hemochromatosis, malnutrition and
  malignancies
• List the reference ranges for Total Iron, TIBC
  and Saturation

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• Iron ( Fe )
• Most abundant trace element
• Iron mostly associated with hemoglobin
• Absorbed in the small intestines
• Iron is conserved Very little is lost ( unless
  bleeding )
• Storage forms of iron
• Ferritin
• Bone marrow, spleen and liver
• ? plasma ferritin is sensitive indicator of Fe
  deficiency

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• Transferrin
• Transports iron from the GI tract to the bone
  marrow and other organ
• Glycoprotein, synthesized in the liver
• Each transferrin molecule transports 2 iron atoms
• Normally only ? of transferrins binding sites
  are occupied
• Iron Deficiency
• Causes
• Inadequate dietary intake
• Blood Loss

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• Iron Overload
• Primary hemochromatosis ( Genetic iron
  accumulation )
• Treatment Therapeutic phlebotomy causes a mild
  iron deficiency

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• Iron testing ( serum )
• Most assays follow these steps
• Disassociate Fe from transferrin with strong
  acid
• Iron is reduced from ferrous to ferric ( Fe3
  Fe2 )
• Addition of ferrozine creates a colored compound
• Measurement of colored product by
  spectrophotometry
• Specimen requirements
• Serum ( hemolysis free )
• Anticoagulants that bind iron are unacceptable
  ( EDTA Sodium Citrate )
• Reference range 65 170 mg / dl

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• Serum ferritin
• Circulating plasma ferritin is proportional to
  iron tissue storage
• Decreased plasma ferritin is a sensitive
  indication of iron deficiency

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• Transferrin
• Plasma iron is bound to transferrin
• Measurement of transferrin indicates the maximum
  amount of iron that could be transported in the
  plasma
• Causes of increased transferrin
• Iron deficiency
• Causes of decreased transferrin
• Inflammation

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• Total Iron Binding Capacity ( TIBC )
• The TIBC is an estimate of transferrin
  concentration
• TIBC is a measurement of how much iron could be
  transported in the plasma by transferrin
  
  ( not how much iron a patient actually has )
• The greater the transferrin concentration, the
  greater the TIBC

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• TIBC methodology
• An excessive amount of iron ( reagent ) is
  added to serum, saturating transferrin
• Excess ( unbound ) iron is removed from the
  serum by adding MgCO3 which precipitates
  unbound iron
• The specimen is centrifuged, spinning the MgCO3
  Fe complex to the bottom
• Test the supernate for iron using the
  traditional Total Iron methodology
• The TIBC measures transferrins maximum ability

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ILLUSTRATION OF TIBC METHODOLOGY
PATIENT PLASMA WITH TRANSFERRIN AND BOUND IRON
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• Iron Profiles include 3 components
• Total Iron ( serum )
• TIBC
• Iron Saturation ( Fe Sat )
• The Iron Saturation is a measurement of how
  full transferrin is

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• Iron Profile Reference Ranges
• Total Iron 65 - 170 ( ?g / dl )
• TIBC 250 - 450 ( ?g / dl )
• Saturation 20 - 55 ( )

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IRON TOP 10

• TIBC Total Iron Binding Capacity
• TIBC is a measurement of the iron transporting
  capacity of transferrin
• Iron Saturation
• Iron Deficiency Total Iron ? TIBC ?
  Fe Saturation ??
• Hemochromatosis Total Iron ? TIBC ?
  Fe Saturation ??
• Infection / Cancer Total Iron ? TIBC ?
  Fe Saturation ??
• Transferrin is a plasma iron transport protein
• Ferritin is a storage form of iron found in cells
  and plasma
• Hemochromatosis is a genetic disease of excessive
  iron accumulation
• Iron is well conserved by the body If lost,
  probably through bleeding

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Iron Links
http//www.umm.edu/blood/aneiron.htm http//www.e
hendrick.org/healthy/000772.htm http//www.nlm.ni
h.gov/medlineplus/ency/article/000584.htm http//
www.healthservices.gov.bc.ca/msp/protoguides/gps/f
erritin.html