Iron Status Markers Flashcards
most abundant essential element in the body
iron!
- part of Hb, myoglobin, cytochromes
- O2 transport
- cellular biochemical processes (e- transfer)
regulation of iron in the body
- small intestine
> intake through diet; heme iron (meat) and inorganic iron (plant)
> conservation of irono stores (recycling of RBCs and hemoglobin); spleen
> liver = hepcidin - transferrin = brings to circulation
iron measurement
- iron in circulation is found bound to transferrin at 2 sites (in oxidized form; 3+)
- colorimetric detection of iron using dye
factors affecting interpretation of iron results
- methods differ a lot = need to define lab-specific reference interval
- diurnal variation = 30% higher in morning
- physiological changes = menstruation, pregnancy, oral contraceptives
- transient increases = diet, hemolysis, environmental contamination
- use serum or heparin plasma; fasting required; DON’T use EDTA as it chelates iron
ferritin
- reflects long-term iron stores in tissues
- measurement using immunoassay
- acute phase reactant = elevated in inflammation, infection, or cancer
transferrin measurement
- directly; immunoassay
> use anti-transferrin Ab
> nephelometric (scattered light) detection is most common - not commonly used bc of high cost, poor standardization, and limited clinical utility
transferrin
- transport of iron into cells via transferrin receptor
- transferrin expression in liver increases with iron deficiency
- negative acute phase reactant = in chronic inflammation/infection or cancer production in liver decreases
preferred transferrin emasurement
- indirect!; transferrin saturation (most common)
- total iron-binding capacity (TIBC)
- unsaturated iron-binding capacity (UIBC)
maximum amount of iron that can be bound in the blood by transferrin
TIBC
- add iron to sample to saturate transferrin binding sites
- unbound iron is removed
- measure the remaining bound iron using iron assay
- calculate saturation index: transferrin saturation index = serum iron/TIBC
maximum amount of iron that can be bound in the blood by transferrin
TIBC
- add iron to sample to saturate transferrin binding sites
- unbound iron is removed
- measure the remaining bound iron using iron assay
- calculate saturation index: transferrin saturation index = serum iron/TIBC
the total amount of unbound iron binding sites in blood
UIBC (unsaturated iron binding capacity)
- add a known excess amount of iron to sample to bind all available unbnd binding sites on transferrin
- assay performed on remaining unbound iron under neutral pH so that only unbound iron is measured
- UIBC is calculated as:
UIBC = iron added - unbound iron
- calculate TIBC:
TIBC = UIBC + serum iron - calculate transferrin saturation
deficiencies in iron
- decreased intake (MOST COMMON): from diet or malabsorption
- increased loss: blood loss, pregnancy/growth
- clinical presentation: impaired RBC production, low iron stores, fatigue
overload in iron
- increased intake: iron supplementation, transfusion
- increase in serum: hemolysis, lead toxicity
- increased tissue damage: genetic defects
- clinical presentation: bronze skin, cirrhosis, diabetes
anemia of chronic inflammation
- seen in chronic infections, chronic immune activation, malignancy
- increase in pro-inflammatory cytokines leads to increases in + acute phase reactants (ferritin) and reduction of other acute phase reactants (transferrin), leading to a reduction in the ability to carry iron in circulation
- ACI and IDA look similar clinically; iron status markers are important to differentiate between the two
- iron status markers return to normal once source of inflammation/infection is resolved
