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Haematology > Iron in Disease > Flashcards

Iron in Disease Flashcards

1
Q

What 2 things is iron essential for?

A
  • Iron transport

* Electron transport

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2
Q

In iron, there is reversible/irreversible O2 binding from Hb

A

Reversible

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3
Q

Ferric

A

Fe3+

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4
Q

Ferrous

A

Fe2+

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5
Q

What 3 things is iron present in?

A
  • Haemoglobin.
  • Myoglobin.
  • Enzymes e.g. cytochromes.
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6
Q

Why is iron dangerous?

A

Due to its chemical reactivity - oxidative stress

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7
Q

Because iron can be toxic to the body, what does the body do to prevent this?

A
  • Safe transport.
  • Safe storage.
  • Regulation of iron absorption.
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8
Q

Iron does NOT have a ….

A

Mechanism of excretion

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9
Q

Iron does NOT have a mechanism of excretion

A

T

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10
Q

What is there in each globin chain?

A

1 haem group

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11
Q

What ion is found in each haem group of every globin chain?

A

Fe2+

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12
Q

Where does the Fe2+ ion in the haem group sit?

A

In the porphyrin ring

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13
Q

Where is the majority of body iron found?

A

In haem

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14
Q

How is haem formed?

A

Protoporphyrin is formed from porphobilinogen

This combines with Fe3+ to form haem.

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15
Q

Porphyrin ring + Fe2+ =

A

Haem

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16
Q

How much iron does the body absorb per day?

A

1mg / day

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17
Q

How much iron exists in:

i) plasma
ii) parenchymal tissues
iii) erythroid marrow
iv) red cell haemoglobin
v) macrophage stores?

A

i) 4mg
ii) 500mg
iii) 150mg
iv) 2500mg
v) 500mg

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18
Q

How much iron is lost per day?

A

1mg

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19
Q

Where does iron absorption occur?

A

In the duodenum

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20
Q

Iron absorption occurs in the _________

A

Duodenum

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21
Q

What is responsible for the transport of IRON INTO the DUODENAL ENTEROCYTE?

A

DMT (Divalent metal transporter) -1

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22
Q

What is the role of FERROPORTIN?

A

Facilitates iron EXPORT from the enterocyte

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23
Q

What happens to iron once it has been exported from he enterocyte?

A

It is passed on to transferrin for transport elsewhere

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24
Q

What is responsible for the down-regulation of ferroportin?

A

Hepcidin

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25
Q

What does hepcidin do?

A

Down-regulates ferroportin to decrease exportation of iron from the enterocyte

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26
Q

The regulation of iron absorption can be grouped into 3 factors, what are these?

A
  1. Intra-luminal factors.
  2. Mucosal factors.
  3. Systemic factors.
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27
Q

What does intraluminal factors for regulation of iron absorption take into account?

A
  • Solubility of inorganic iron.
  • Haem iron is easier to absorb.
  • The reduction of (Fe3+) to ferrous (Fe2+)
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28
Q

What does mucosal factors refer to?

A

The expression of iron transporters

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29
Q

Give examples of 2 iron transporters (used in the regulation of iron absorption).

A
  • DMT-1 (divalent metal transporter) - at mucosal surface.

* Ferroportin - at serosal surface.

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30
Q

Where is ferroportin found?

A

At serosal surface

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31
Q

Where is DMT-1 found?

A

At mucosal surface

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32
Q

What is the major systemic factor which regulates iron absorption?

A

HEPCIDIN

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33
Q

What is hepcidin?

A

The major NEGATIVE REGULATOR of iron uptake.

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34
Q

_________ is the major NEGATIVE REGULATOR of iron uptake.

A

Hepcidin !!!

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35
Q

Where is hepcidin produced?

A

In the liver

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36
Q

What is hepcidin produced in response to?

A
  • Iron overload

* Inflammation

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37
Q

What does hepcidin do?

A

Down-regulates ferroportin

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38
Q

What is the result of hepcidin (down-regulating ferroportin)?

A

Iron is ‘trapped’ in duodenal cells and macrophages.

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39
Q

How many compartments are there in the assessment of iron status?

A

3

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40
Q

What are the 3 compartments in the assessment of iron status?

A
  1. Functional iron - haemoglobin concentration.
  2. Transport iron/iron supply to tissues - % saturation of transferrin with iron.
  3. Storage iron - serum ferritin / tissue biopsy (rarely needed).
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41
Q

Describe the structure of transferrin.

A

A protein with 2 binding sites for iron atoms

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42
Q

What does transferrin do?

A

Transports iron FROM donor tissues (macrophages, intestinal cells and hepatocytes) TO tissues expressing transferrin receptors.

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43
Q

What area of the body is rich in transferrin receptors?

A

Erythroid marrow

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44
Q

What measures iron supply?

A

Transferrin saturation

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45
Q

Transferrin saturation measures _____ ______

A

Iron supply

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46
Q

How is transferrin saturation calculated?

A

Serum iron/total iron binding capacity (to transferrin) x 100%

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47
Q

What does transferrin saturation reflect?

A

Reflects proportion of diferric transferrin (high affinity for cellular transferrin receptors

48
Q

What is unbound transferrin called?

A

Apotransferrin

49
Q

What is iron bound to transferrin called?

A

Holotransferrin

think it is (w)hole when bound to transferrin

50
Q

What is a normal transferrin saturation?

A

20-50%

51
Q

In iron overload, transferrin saturation increases/decreases

A

Increases

52
Q

In iron deficiency, transferrin saturation increases/decreases

A

Decreases

53
Q

Describe the structure of ferritin.

A
  • Spherical intracellular protein (450kDa).

* Stores up to 4000 ferric ions (Fe3+)

54
Q

Why can serum ferritin be used to measure storage iron?

A

A tiny amount of serum ferritin reflects intracellular ferritin synthesis.

It is an INDIRECT MEASURE OF STORAGE IRON

55
Q

What is ferritin involved in?

A

Iron storage

56
Q

In what 2 situations is iron increased?

A
  • Iron overload

* Inflammation

57
Q

Ferritin is ____ in iron deficiency

A

LOW

58
Q

Ferritin is _____ in iron overload

A

HIGH

59
Q

State 3 broad groups of disorders of iron metabolism.

A
  • Iron deficiency.
  • Iron malutilisation – ‘anaemia of chronic disease.’
  • Iron overload.
60
Q

Outline the consequences of negative iron balance, in order as they progress over time.

A
  1. Exhaustion of iron stores
  2. Iron deficient erythropoiesis - falling red cell MCV
  3. Microcytic anaemia
  4. Nail changes - skin, angular stomatitis, koilonychia
61
Q

What do Hypochromic Microcytic Anaemias occur due to?

A

Deficient haemoglobin synthesis

62
Q

Outline the 2 main groups of causes of deficiency haemoglobin synthesis.

A
  1. Haem deficiency

2. Globin deficiency

63
Q

What are the 3 main groups of causes of haem deficiency?

A
  • Iron deficiency
  • Anaemia of chronic disease
  • Congenital sideroblastic anaemia
64
Q

A combination of what CONFIRMS iron deficiency?

A

A combination of anaemia (decreased HAEMOGLOBIN IRON) and reduced storage iron (low SERUM FERRITIN).

65
Q

Anaemia + low ferritin =

A

Anaemia

66
Q

Outline the main causes of iron deficiency.

A
  • Insufficient intake
  • Loosing too much e.g bleeding
  • Not absorbing enough
67
Q

Who, is more susceptible to insufficient intake of iron?

A
  • Women

* Children

68
Q

Suggest the main causes of chronic blood loss.

A
  • Menorrhagia
  • GI
  • Haematuria
69
Q

What GI conditions can cause chronic blood loss?

A
  • Tumour
  • Ulcer
  • NSAID
  • Parasitic infection
70
Q

What is occult blood loss?

A

Small amounts of blood can be lost (usually from the GI tract), without the patient experiencing any symptoms

71
Q

What volume of GI blood loss can occur per day without any signs or sx of bleeding?

A

8-10mls i.e 4-5mg of iron

72
Q

What is the max dietary absorption of iron?

A

Around 4-5mg per day.

73
Q

What essentially is iron malutilisation?

A

Anaemia of chronic disease.’

74
Q

Outline the process of normal haemoglobin recycling?

A

Haemoglobin is broken down into its haem and globin components.

Globin: broken down into amino acids
Haem: broken down into porphyrin and iron

The porphyrin is then further broken down to bilirubin. The iron is either stored as ferritin, or transported as transferrin to marrow erythroblasts.

75
Q

‘Inflammatory macrophage iron block’ is seen in what condition?

A

Anaemia of chronic disease

76
Q

Outline the inflammatory macrophage iron block which occurs in anaemia of chronic disease.

A
  1. Increased transcription of ferritin mRNA stimulated by inflammatory cytokines so ferritin synthesis is increased.
  2. Increased plasma hepcidin blocks ferroportin-mediated release of iron.
  3. Results in impaired iron supply to marrow erythroblasts and eventually hypochromic red cells.
77
Q

Causes of iron overload can be _________ or __________

A
  1. Primary

2. Secondary

78
Q

Name a primary cause of iron overload.

A

Hereditary haemochromatosis

79
Q

Name a secondary cause of iron overload.

A

Transfusional; iron loading anaemias

80
Q

What is primary iron overload?

A

Long-term excess iron absorption with parenchymal rather than macrophage iron loading

81
Q

What is the commonest gene to cause hereditary haemochromatosis?

A

Mutations in HFE gene

82
Q

What do mutations of the HFE gene result in?

A

Decreased synthesis of hepcidin

83
Q

What does decreased synthesis of hepcidin result in?

A

Increased iron absorption

84
Q

What is the effect of chronic increased absorption of iron?

A

Gradual iron accumulation with risk of end organ damage

85
Q

What are the clinical features of hereditary haemochromatosis?

A
  • Weakness/fatigue.
  • Joint pains.
  • Impotence.
  • Arthritis.
  • Cirrhosis.
  • Diabetes.
  • Cardiomyopathy.
86
Q

When does hereditary haemochromatosis usually present?

A

In middle age, or later

87
Q

What is classified as ‘iron overload’?

A

> 5mg

88
Q

How is molecular diagnosis of hereditary haemochromatosis achieved?

A

By identifying mutations of HFE gene

89
Q

HFE gene mutations account for ___% of HH

A

95%

90
Q

HFE gene mutations show ___________ penetrance

A

INCOMPLETE

91
Q

When would you be concerned about risks of iron overloading?

A

If transferrin saturation is >50%

sustained on repeat fasting sample

92
Q

What qualifies as increased iron stores?

A

Serum ferritin:

> 300 mg/l in men.
or
200 mg/l in pre-menopausal women.

93
Q

When, in HH, should you do a liver biopsy?

A

Only if uncertain about iron loading or to assess tissue damage

94
Q

What is the treatment of HH?

A

Weekly venesection

95
Q

How much blood should be venosected during the weekly venesection of someone with HH?

A

450-500ml

i.e 200-250mg of iron

96
Q

How is HH diagnosed?

A 
* Transferrin saturation >50%
\+
Serum ferritin:
>300 mg/l in men. 
or 
>200 mg/l in pre-menopausal women.
97
Q

What is the aim of weekly venesection in HH patients?

A
  • Initially - aim to exhaust iron stores (ferritin <20 µg/l)‏
  • Thereafter – keep ferritin below 50 µg/l
98
Q

What do people with HH die of?

A

Hepatoma

99
Q

If someone is diagnosed with HH, who in their family is offered screening?

A

First degree relatives, especially siblings – risk is 1 in 4.

100
Q

Should children be screened for HH if a relative is diagnosed?

A

No – wait until they are adults and able to give informed consent.

101
Q

How is screening for HH carried out?

A

HFE genotype and iron status.

  • Ferritin and transferrin saturation.
102
Q

Why is familiar screening so important in HH?

A

Haemochromatosis may be asymptomatic until irreversible organ damage has occurred

Better to screen, catch early, and treat quick

103
Q

What are the potential sources of iron-loading anaemias?

A
  • Repeated red cell transfusions.

* Excessive iron absorption, related to over-active erythropoiesis.

104
Q

What 2 groups of disorder may result in iron overloading anaemia?

A
  1. Massive ineffective erythropoiesis.

2. Refractory hypoplastic anaemia

105
Q

Give examples of conditions that cause massive ineffective erythropoiesis.

A
  • Thalassaemia syndromes.

* Sideroblastic anaemias.

106
Q

Name 2 conditions under the heading of ‘refractory hypo plastic anaemia’

A
  • Red cell aplasia.

* Myelodysplasia (MDS).

107
Q

How much iron does each unit of blood contain?

A

250 mg

108
Q

How often may patients with thalassaemia require transfusion?

A

Every 2-3 weeks. lifelong

109
Q

What is transfusion need in myelodysplasia like?

A

Highly variable

110
Q

What qualifies as ‘iron overload’ in terms of

i) total
ii) liver dry weight?

A

i) >5g.

ii) >15mg/g dry weight.

111
Q

What can iron overload result in damage to?

A

Liver, heart and endocrine glands.

112
Q

Iron overload is inevitable and predictable with regular red cell transfusions, but risk of excess intestinal iron absorption may be hidden until tissue damage becomes symptomatic.

A

T

113
Q

What tx is NOT an option in secondary iron overload?

A

Venesection – not ok if pt is already anaemic

114
Q

What is the treatment for secondary iron overload?

A

Iron chelating agents

115
Q

Given examples of iron chelating agents.

A
  • Desferrioxamine (subcut or IV infusion).

OR newer oral agents:

  • Deferiprone.
  • Deferasirox.

Haematology (26 decks)

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