Perhaps the most common blood test you will review daily will be the FBC (full blood count). You will commonly see a low haemoglobin & the tendency is to say “haemoglobin stable” and ignore it. However, both acute or chronic anaemia can have a significant impact on health but can also be the presenting sign of a serious underlying condition.

Untreated anaemia can lead to an increased risk of illness, infection, heart failure & a poorer ability to recover following critical illness. Poor endurance and exercise tolerance from anaemia can also make it difficult to engage with physiotherapy & discharge planning.

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Emergency Anaemia

The first thing to consider is whether the anaemia may be life-threatening – always have a low threshold for an ABCDE assessment. Concerning features include: 

  • Haemodynamic instability 
  • An acute drop (particularly in surgery as this could suggest internal or external bleeding)
  • Symptomatic anaemia (as this suggests the drop is acute)
  • Those with a high risk of bleeding (on anticoagulants or bleeding disorders)
  • Suspected or confirmed ACS (often aim for Hb target of 80 rather than 70)

For severe bleeding or major haemorrhage, you may need to activate the major haemorrhage protocol if one exists & call the emergency team.

Non-Emergency Anaemia

On detection of anaemia, regardless of the MCV, most people would do the minimum of a blood film and haematinics (B12, folate & iron tests – ferritin, TIBC, transferrin). This must be done prior to transfusion. Further assessment usually takes into account the size of the cells to focus on relevant history & investigations.

General Assessment
  • Check if the anaemia is new by comparing against historic blood tests
  • Ask about their diet (as haematinic deficiency is incredibly common)
  • Ask if there is any blood loss (or risk factors for blood loss)
  • Family history of anaemia and ethnicity (?haemoglobinopathies)
  • Previous blood transfusion (and if there are any special requirements)
  • Symptoms of anaemia (including ECG for ?ischaemic features)
  • Cardiac diseases (due to transfusion reactions e.g. TACO) as furosemide may be required
  • Weight
Microcytosis (low MCV)

Consider iron deficiency, haemoglobinopathies or malignancy. Anaemia of inflammation can also cause microcytosis e.g. heart failure, CKD or rheumatoid arthritis.

For iron tests, remember that in acute inflammation, ferritin will increase and transferrin will decrease. Thus they can mask iron deficiency but a low ferritin is highly valuable in identifying true iron deficiency.

If you find the patient is iron deficient, take a careful history to identify if this is dietary, due to poor absorption (coeliac, IBD) or blood loss (GI blood loss e.g. risk factors for upper GI or lower GI bleeding, menstrual bleeding or malignancy). You must ask the red flags for malignancy.

Investigations include:

  • Urine dip for haematuria (?urological malignancy)
  • Upper/lower endoscopy (if 50+ years of age)
  • Coeliac serology
  • H pylori (if dyspepsia or concerns of upper GI bleeding)
  • CT Chest-Abdomen-Pelvis (if there are any red flags)
  • Haemoglobinopathies (if non-caucasian ethnicity & more severe microcytosis e.g. below 75)

Beware of normocytic anaemia with a large red cell distribution width (RDW) as this suggests the cells are at both extremes of size i.e. mixed microcytic & macrocytic picture. Also early or partially treated haematinic deficiency can also result in normocytosis. If you always check haematinics, you cannot go wrong.

The reticulocyte count can tell you whether there is appropriate increased red cell production (reticulocytes are immature RBCs) which might be due to blood loss or haemolysis. A raised LDH, reduced haptoglobin & a blood film with typical features could support a diagnosis of haemolysis.

A low reticulocyte account could suggest bone marrow failure or anaemia of chronic disease/inflammation. Features further supporting this would be multiple cell lines affected (white blood cells, platelets) with normal haematinics. This would merit haematology referral for consideration of bone marrow aspiration.


This is usually due to alcohol, B12/folate deficiency or liver disease. More rarely, causes could include hypothyroidism, chemotherapy agents or myelodysplastic syndromes.

Similar to iron deficiency, folate deficiency could be due to dietary intake, malabsorption or increased utilisation (pregnancy, malignancy). Some medications such as sulfasalazine can impair absorption.

It is worth treating B12 deficiencies even at the lower end of normal. Similar to folate & iron deficiency, inadequate intake or issues with absorption could be the underlying cause. If the patient has other autoimmune conditions, consider pernicious anaemia (antibodies for parietal cells & intrinsic factor).

Treating Haematinic Deficiencies

Ensure you check NICE guidelines & the BNF for the latest & most accurate information. When initiating replacement, ensure you let the GP know you have started the treatment so that they can continue monitoring in the community. Treatment is often continued 3 months after the haemoglobin is within normal range & then rechecked a few months after stopping.

Iron replacement

Oral therapy includes ferrous sulphate or fumarate. Giving more than 1 tablet per day tends to cause significant GI side effects without an increase in absorption (a spike in hepcidin reduces absorption). Instead, taking the iron with a source of vitamin C whilst avoiding things that impair absorption (e.g. tea) are thought to be more effective. Beware that iron interacts with many other medications such as Adcal, levothyroxine & levodopa thus shouldn’t be taken at the same time.

IV therapy (e.g. monofer or ferinject) is useful for:

  • Those unable to tolerate the GI side effects
  • Those with impaired absorption due to inflammatory state or GI pathology
  • Those requiring prompt iron replacement to avoid transfusion

It is generally avoided in acute infection. Note for ferinject, you can only give a maximum of 1000mg and if further replacement is required, it will need to be given after 1 week. IV iron takes more than 6-8 weeks to achieve a complete response.

Folate replacement

Ensure you replace B12 deficiency first. Typically folic acid 5mg OD for at least 4 months.

B12 replacement
  • Oral: Cyanocobalamin 50 – 150 micrograms OD PO, between meals
  • IM: Hydroxocobalamin 1 mg 3 x per week for 2 weeks, then 1 mg every 2-3 months

Written by Dr Victoria Lowe (FY3), Dr Smiji Saji (FY1) & Dr Akash Doshi (ST3)

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