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Haematology > Iron > Flashcards

Iron Flashcards

1
Q

what are the roles of iron

A 
oxygen transport (reversible binding to Hb)
electron transport (for ATP production in mitochondria)
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2
Q

what is iron present in

A 
haemoglobin (majority)
myoglobin 
enzymes: cytochromes 
macrophage
liver stores (parenchymal tissue)
erythroid marrow 
plasma
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3
Q

why is iron dangerous

A

causes oxidative stress

no mechanism for excretion

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4
Q

what is the structure of Hb

A

haem (Fe2+ in porphyrin ring) group in each globin chain

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5
Q

how much iron is absorbed per day

A

1mg

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6
Q

where is most iron stores

A

red cell Hb

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7
Q

how much iron is lost per day

A

1mg (e.g. shedding of skin)

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8
Q

where does iron absorption occur

A

mainly in the duodenum - into mucosa cells

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9
Q

what enhances iron absorption

A 
ascorbic acid (vit C -> reduces Fe2+ to form DMTI protein)
alcohol 
haem iron (iron from meat, has specific transporter compared to veggie iron)
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10
Q

what inhibits iron absorption

A

tannins (tea)
phytates (cereals, bran, nuts and seeds)
calcium

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11
Q

how is iron absorbed

A

duodenal cytochrome B (found in luminal surface, reduces ferric acid (Fe3+) to ferrous (Fe2+))

DMT (divalent metal transporter, transports into duodenal enterocyte)

ferroportin (facilitates export from enterocyte, passed onto transferrin)

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12
Q

what regulates iron absorption

A

hepcidin
(negative regulator, produced in liver in response to increased iron load and inflammation. binds to ferroportin and degrades it making iron trapped in duodenal cells and macrophages)

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13
Q

how do you assess functional iron

A

Hb conc (most iron present in Hb)

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14
Q

how do you asses transport iron/ iron supply to tissues

A

% saturation of transferrin with iron

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15
Q

how do you assess iron stores

A 
serum ferritin 
tissue biopsy (rarely needed)
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16
Q

what is transferrin

A

protein with two binding sites for iron atoms that transports it from donor tissues (macrophages, intestinal cells, hepatocytes) to tissues expressing transferrin receptors e.g erythroid marrow

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17
Q

what does transferrin saturation measure

A

iron supply

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18
Q

how do you calculate transferrin saturation

A

serum iron / total iron binding capacity x 100%

19
Q

what is normal transferrin saturation

A

20-50%

20
Q

what happens to transferrin in iron overload

A

saturation is elevated (max 100%)

21
Q

what happens to transferrin in iron deficiency

A

saturation is decreased

22
Q

what is ferritin

A

intracellular protein that store

23
Q

what does serum ferritin indicate

A

intracellular ferritin synthesis= INdirect measure of storage iron

24
Q

what else can raise ferritin

A

acts as an acute phase protein- malignancy, infection, liver disease etc

25
Q

what happens to ferritin in iron overload and deficiency

A

deficiency- decreased

overload- increased

26
Q

what can cause iron malutilisation

A

anaemia of chronic disease

27
Q

what are the consequences of a negative iron balance (low intake/ malutilisation)

A

exhaustion of iron stores
iron deficient erythropoiesis: falling red
cell MCV
microcytic anaemia
epithelial changes: skin, koilonychia, angular stomatitis

28
Q

what causes hypochromic microcytic anaemia

A

deficient Hb synthesis:

  • haem deficiency= lack of iron for erythropoiesis (deficiency, anaemia of chronic disease (normal body iron))
  • congenital sideroblastic anaemia (rare)

-globin deficiency (thalassaemias)

29
Q

how is iron deficiency confirmed

A

combination of anaemia (decreased Hb iron) and reduced storage iron (low serum ferritin)

30
Q

what can cause iron deficiency

A

insufficient intake to meet physiological need (more likely in women and children as greater need)

  • diet
  • chornic bleeding: menorrhagia, haematuria (kidney tumour), GI: tumours, ulcers, NSAIDs, parasitic infections, occult
  • malabsorption: coeliac disease
31
Q

what is occult blood loss

A

GI blood loss of 8-10ml per day (4-5ml iron) without any signs or symptoms
(def can occur as max dietary intake is 4-5mg/day)

32
Q

is iron def anaemia a symptom or a diagnosis

A

symptoms (replacement therapy may relive symptoms without treating underlying cause)
Ix essential
early surgery for GI tumours curative

33
Q

what is the pathophysiology of anaemia of chronic disease

A

inflammatory macrophage iron block:
increased ferritin mRNA due to inflammatory cytokines
increased ferritin synthesis
increased plasma hepcidin blocks ferroportin mediated release of iron
=impaired iron supply to marrow erythroblasts
=hypochromic red cells

• Iron stores in macrophages and duodenal cells increase due to:
- Raised inflammatory cytokines upregulate ferritin
- Raised hepcidin blocks the ferroportin-mediated release of iron from cells
• Total iron is not changing but it is just stuck in placed that you can’t use it
• This is done to prevent bacterial from using iron in blood to grow

34
Q

what are the causes of iron overload

A

primary: heriditary haemochromatosis
secondary: transfusional, iron loading anaemias

35
Q

what causes primary ion overload

A

long term excess iron absorption with parenchymal rather than marcophage iron loading

(hereditary haemochromatosis= HH)

36
Q

what causes HH

A

most commonly caused by mutations in HFE gene (AR)
decreased synthesis of hepcidin
=increased iron absorption
=gradual iron accumulation with risk to end organ damage

37
Q

what are the clinical features of HH

A 
weakness/ fatigue 
joint pains 
impotence 
arthritis 
cirrhosis 
diabetes 
cardiomyopathy

present in middle age or later
can be asymptomatic untill end organ damage has occurred
iron overload >5g

38
Q

how is HH diagnosed

A

> 50% transferrin saturation that is sustained on repeated samples
increased serum ferritin >300 (men), >200 (pre menopausal women)

(liver biopsy hardly used, fibroscan for cirrhosis)

39
Q

what is the treatment for HH

A 
weekly venesection (450-500mls = 200-250mg iron)
want ferritin <20 initially then aim to keep it below 50 by venesection 2/3 times a year

siblings have 1 in 4 chance- test children
(screening= genetic test (HFE genotype) + iron status (ferritin and transferrin saturation)

40
Q

what are the most common causes of death in HH

A 
hepatoma 
hepatic failure/bleedinf varices 
cardiac dailure 
infections 
diabetes
41
Q

what can cause iron loading anaemias

A
  • repeated red cell transfusions
  • excessive iron absorption due to overactive erythropoiesis
disorders: 
massive but ineffective erythropoiesis:
-thalassaemia 
-sideroblastic anaemias (cant incorperate iron into haem)
refractory hypoplastic anaemias:
-red cell aplasia 
-myelodysplasia
42
Q

how much iron does each unit of blood contain

A

250mg

43
Q

how often do you need transfusions in thalassaemias

A

2-3 weekly lifelong

44
Q

what is the treatment for secondary iron overload

A 
cant vensect if patient already anaemic 
use iron chelating agents: 
-desferrioxamine (s/c or IV)
-deferipone oral 
-deferasirox oral 
(often compliance problems)

Haematology (27 decks)

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