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Investigation and diagnosis

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

A full clinical history and physical examination should be undertaken.

  • inquire about
    • use of aspirin and other NSAID's
    • family history of IDA - may indicate inherited disorders of iron absorption
    • haematological disorders e.g. - thalassaemia
    • telangiectasia and bleeding disorders
    • family history of colorectal carcinoma (1,2)

  • consider if patient meets either
    • criteria for urgent cancer referral or
    • use of faecal immunochemical test (FIT) in symptomatic patients outside urgent cancer referral guidance
    • see linked items

In patients with no obvious cause for iron deficiency anaemia (IDA), the following investigations could be carried out (2):

  • coeliac serology (presence of anti-endomysial antibody or tissue transglutaminase antibody) - The British Society of Gastroenterology suggests that all patients with IDA should be screened for coeliac disease

  • upper and lower GI investigations - in all postmenopausal female and all male patients in whom iron deficiency has been confirmed (except when there is a history of significant overt non GI blood loss)

  • urine testing for blood - since around 1% of patients with IDA will have renal tract malignancy

  • stool examination - if appropriate to detect parasites

  • testing for Helicobacter pylori - H. pylori colonisation may impair iron uptake and increase iron loss

  • faecal immunochemical test (FIT):
    • FIT in symptomatic patients outside urgenct cancer referral guidance (2 week wait criteria) (3)
      • NICE criteria for requesting test for occult blood in faeces (FIT)
        • should be offered to adults without rectal bleeding who:
          • are aged 50 or over with unexplained:
            • abdominal pain or weight loss or
          • are aged under 60 with:
            • changes in their bowel habit or iron-deficiency anaemia or
          • are aged 60 or over and have anaemia without iron deficiency
      • the the level of Hb used for an abnormal versus a normal result my vary with respect to implementation of this pathway
        • a level of greater than or equal to 10 µg Hb/g faeces for defining an "abnormal result" has been suggested by NICE
        • an "abnormal test" meets the criteria for urgent cancer referral (3)

Investigations in IDA include the following:

  • full blood count and blood film examination
  • recognise the indices of iron deficiency
    • reduced haemoglobin - Men <13.5 g/dl, women < 11.5 g/dl
    • reduced MCV - <76 fl (76–95 fl )
    • reduced MCH - 29.5 ± 2.5 pg (27.0–32.0 pg)
    • reduced MCHC - 32.5 ± 2.5 g/dl (32.0–36.0 g/dl) (1)
  • blood film
    • microcytic, hypochromic cells
    • occasional target cells and pencil-shaped poikilocytes
  • platelet count may be at or above the upper limit of normal if there is persistent bleeding
  • haematinic assays:
  • decreased serum ferritin - best biochemical marker (in the absence of inflammation)
    • the cut off concentration that is diagnostic varies between 12 and 15 mg/l.
    • but in the presence of an inflammatory disease a concentration of 50 mg/l or even more may still be consistent with iron deficiency
  • vitamin B12, folate
  • increased serum transferrin receptor (sTfR) assay - is a good indicator of iron deficiency in instances where ferritin estimation is likely to be misleading but its value in the clinical setting remains to be proven (1).
  • serum iron and total iron binding capacity (TIBC)

The best proof of iron deficiency anaemia is that the anaemia is cured by administration of iron.


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