B 12 Flashcards
Holotranscobalamin - what is
Transcobolamin bound to b12
Active
25% b12
What is haptocorrin
Glycoproteins binds 75% b12
Holohaptocorrin
What Changes total B 12
Change in binding protein
Metabolic function of b12
Last step in fatty acid digestion-
2 methylmalonyl A to succinyl co A
If this doesn’t happen in mitochondria- mma leaks out
2- making methionine w homocysteine- this will also be elevated in folate def
Genetic haptocorrin def
Low total b12 bug normal tissue b12(Holo TC)
No clinical manifestation b12
Found in 15% w low total b12
Clinical indications for b12 testing
Macrocytic anaemia Anaemia of chronic kidney diseases Cognitive de Dementia Polyneuropathy Chronic fatigue syndrome
What is good negative predictor of b12 def
Normal mma/homocysteine
Plasma homocysteine limitations
Non fasting Ageing/rénal impairment Smoking, coffee wine Low folate/Vit B6 Hyper proliferation d/o Genetic defect
High npv
Mla limitations
Elderly
Rénal failure
Urine mma more influenced by good than plasma
Hypocolaemia
Anti if ab
Near 100% spec for PA
50-70% sens
Transferrin sat < 15%
Latent iron deficiency
Timing iron studies
Early am fast
Because dietary iron can inc iron- this is used in calculation of t sat gives false result
sTFr in fe def
Increased
Not affected by infection
sTFr in pgy
Increased due to inc stimulation of eryhtropoeisis and inc iron requirements by iron dependant cell proliferation
Can be used in pgy
Not affected by post partum inflammation like ferritin
Useful I’m unclear situations in pgy
McV in pgy
Falsely high due to inc erythropoeisis so not reliable for fe def
TIBC in pgy
Raised
What can lower tibc
Infl Chronic infxn Malignancy Liver disease Nephrotic syndrome Malnutrition
sTFr
86% sen 75% spec
Not standardised
Is a truncated fragment of membrane receptor
Hepcidin in iron homeostasis
Inhibits iron entry into plasma from gut, macrophages
Deficiency causes iron overload
Interacts w ferroportin to control iron flow- causes it to internalise and degrade
Iron excess causes ? Hepcidin
Inc production
Iron
Colorimetric assay
Ferrizyme binds to iron and get colour change
False high iron
Haemolysis
Transferrin assay
Immunoturbidometric
Human t ferrin forms precipitate w antiserum which is determined turbidemetrically
Measure might- more précipitante there is less light so inv proportional to ferritin
Interférence w ferritin
High level paraprotein
Biotin
Ferritin assay
Colourimetric sandwich assay
Solid phase
