Iron

iron metabolism

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Functional Iron Deficiency (Anaemia of Chronic Disease)

 

Insufficient iron incorporation into erythroid precursors, despite apparently adequate iron stores (Normal ferritin and BM iron stores).

 

ACD thought to be intended as a short-term effort to deprive pathogens of free iron, and to allow increase white cell production at the expense of red cells. Becomes a pathological process once occurring chronically.

 

Serum Ferritin

 

(N.B. There is now a 2018 BSH guideline exclusively for the Ix of raised ferritin (see here))

 

A surrogate measure of the intracellular stored ferritin, not of usable circulating iron.

Ferritin 1ug/l = 8mg of stored iron

 

A normal/raised ferritin is not equivalent to sufficient iron being made available to erythroblasts

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CKD Patients (NICE 2015)

 

Serum ferritin is not useful in CKD - elevated in 50% of patients on haemodialysis but not reflective of bioavailable iron. Therefore:

 

Hb <110g/l + Ferritin 200-800 --> Give IV iron for functional iron deficiency

Hb <110g/l + Ferritin <200 (HD) or <100 (no HD) --> Give IV iron for true iron deficiency

Ferritin >800 --> investigate for iron overload

 

Iron Supplements

 

Traditional recommended oral dose = 100-200mg elemental iron/day

Increasing evidence that this is inefficient, as the amount of iron absorbed from any one dose reduces the closer doses are to one another.

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Iron Deficiency in Pregnancy

 

Daily iron requirement = 1-2mg per day

In 3rd trimester increases = 6mg per day

 

15% of dietary iron is absorbed, increases to 45% in 3rd trimester

 

Definitions of anaemia:

-       1st trimester               <110g/l

-       After 1st trimester     <105g/l

-       Postpartum                <100g/l

 

Indications for testing ferritin prior to treatment

-       Anaemic women when:

o   Known haemoglobinopathy

o   Prior to IV Iron

-       Non-anaemic women when:

o   Previous anaemia

o   Multiparous (>3)

o   Consecutive pregnancies <1 year apart

o   Vegetarians

o   Teenagers

o   Recent bleeding

o   High risk of bleeding or Jehovah’s witness

 

Indications to treat:

-       Oral iron trial if Hb <110 at booking or <105 at 28 weeks

o   Only check ferritin first if known Hbpathy (then proceed if <30)

o   Re-check after 4 weeks, Hb should rise by >20g/l

o   Continue for 3 months and for at least 6 weeks postpartum

-       Offer low dose 65mg/day if non-anaemic risk group from list above

 

Further tests to assess FID/ACD

 

% Hypochromic red cells

-       >6% suggests FID in CKD patients who are on ESA’s

Reticulocyte MCH (CHr)

-       >32pg indicates adequate iron incorporation into reticulocytes

Red blood cell size factor (Rsf)

-       Relates MCV of RBC to that of reticulocytes. >87 fl suggests ACD rather than iron def

Zinc protoporphyrin (ZPP)

-       Trace byproduct or haem synthesis. Used to monitor response to therapy.

 

Further tests to assess iron stores

 

Soluble transferrin receptor (sTfR)

-       Increased in true iron deficiency. Expensive test, poor availability

Hepcidin Assay

BM aspirate for Pearl’s stain

 

Iron Overload

 

Simplified iron overload

Normal / Low Ferritin with Normal/low transferrin sats --> No iron overload

High Ferritin with Normal/low transferrin sats --> Inflammatory state (or rare causes)

Any level of Ferritin with High transferrin sats --> Test HFE Gene Mutation

 

The risk of cardiac iron overload is associated with conditions of reduced erythropoiesis

 

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Type 1 Genetic Haemochromatosis

See separate notes on GH here

 

Rare Causes of Iron Overload

 

Type 2 Haemochromatosis (Juvenile Haemochromatosis)

HFE2 (syn. HJV) or HAMP gene mutations.

Causes severe iron overloading with cardiac failure and panhypopituitarism.

 

Type 3 Haemochromatosis (Transferrin receptor 2 deficiency)

TFR2 mutation.

European and Japanese ethnicities.

Clinical phenotype lies between Type 1 and Type 2 GH.

 

Type 4a Haemochromatosis (Ferroportin Disease)

Loss of function mutation in SLC40A1 (syn. FPN1) gene that encodes ferroportin

Reduced macrophage iron release --> RES iron overload.

Organ damage does not occur but patients develop iron deficiency anaemia with venesection.

 

Type 4b Haemochromatosis

Gain of function SCL40A1 mutation.

Similar phenotype to Type 1 GH.

 

Type 5 Haemochromatosis

FTH1 gene mutation.

Described in a single Japanese family.

 

Aceruloplasminaemia

CP gene mutation

Dystonia, ataxia, dementia (iron deposition in basal ganglia).

 

Hereditary Hyperferritinaemia Cataract Syndrome (HHCS)

Autosomal dominant

L-ferritin deposition in the ocular lens results in early-onset cataracts

There is no need to lower the SF level

 

African Iron Overload

Iron pots used for home brewing beer

 

Neonatal haemochromatosis

Related to acute liver injury, may have alloimmune element

 

Atransferrinaemia

TF gene mutation (Autosomal recessive)

Presents a birth with severe iron deficiency anaemia + paradoxical tissue iron overload

 

Benign Hyperferritinaemia

FTL gene mutation

Ferritin 400 - 6000 without tissue iron overload.

 

Gaucher Disease

See here

 

Iron Chelation

 

1 unit RBC = 200-250mg iron

 

Context (2016 NHS England policy document):

-       Sickle Cell

o   12,500 SCD in UK, 80% living in London, 9% on LT transfusion programme

o   40% of the 9% are on chelation à 450 people

-       Thalassaemia

o   1,500 thal pts in UK, 50% transfusion dependent

o   60%  on chelation (this more than the 50% on transfusion due to non-transfusion dependent Thal (NTDT) patients still prone to iron overload.

-       Both figures will increase in future with birth rate and increased survival

 

Aims:

1.     Prevent harmful effects of free iron

2.     Prevent or reverse organ damage

3.     Maximise quality of life

4.     Prolong survival

 

When to start?

-       After first 10-20 units RBC

-       Or when ferritin >1000 ng/ml

-       Or MRI Liver demonstrates >7mg/gram of dry weight iron loading

 

Desferrioxamine (Desferol) DFO

-       SC/IV injection or continuous infusion. Only works whilst infusing

-       20-60mg /kg / day

-       Ideally given as portable SC infusion for 8-12 hours daily (longer if tolerated)

-       Side effects

o   Hearing / Visual impairment (3 monthly screening mandated)

o   Yersinia infection (mimic appendicitis)

o   Arthralgia / Myalgia

-       SE are reducing by maintaining ratio of Mean Daily Dose (mg/kg) / ferritin below 0.025

 

Deferiprone (Ferriprox) DFP

-       Oral

-       75-100mg/kg/day TDS

-       2nd line license – as monotherapy if Desferol contraindicated or inadequate

-       Superior improvement in cardiac function than desferrioxamine

-       Side Effects

o   GI disturbance

o   Small joint arthritis

o   Agranulocytosis – weekly FBC for neutrophils. Re-challenge not recommended

 

Deferasirox (Exjade, Jadenu) DFX

-       Exjade - Oral dispersible tablet, OD, 10-40mg/kg/day

-       Jadenu – Coated tablet, 1/3 the dose of Exjade, usually better tolerated (fewer GI SE)

-       Better tolerated but slower change in free iron levels

-       Side effects

o   GI disturbance / ulcers

o   Rash

o   Transaminitis

o   Renal impairment