Iron deficiency anaemia in an older man: investigate the bowel
The case
A 66-year-old man presents with 3 months of progressive fatigue and exertional dyspnoea. He takes no regular medication, is a former smoker, and has lost 5 kg over 6 months without abdominal pain or change in bowel habit. There is no visible bleeding. He is pale; abdominal and rectal examinations are normal. Haemoglobin is 95 g/L (130–180), MCV 72 fL (80–100), MCHC 310 g/L (320–360) and platelets 420 × 10^9/L (150–400). Ferritin is 8 micrograms/L (30–400), serum iron 5 micromol/L (10–28) and transferrin saturation 8% (20–50%). A single immunochemical faecal occult blood test is negative. What is the most appropriate next step?
Options
- AUrgent colonoscopy with biopsy
- BUpper gastrointestinal endoscopy instead
- CBone marrow examination
- DRepeat faecal occult blood testing
- EOral iron and recheck haemoglobin
Think it through before you read on. Which single option is best, and why are the other four wrong?
Show the answer and explanation
Answer
A. Urgent colonoscopy with biopsy
Why this is the right answer
This is unequivocal iron deficiency anaemia: microcytic, hypochromic red cells, very low ferritin, low transferrin saturation and a reactive thrombocytosis. In a man of any age, and in a woman after menopause, iron deficiency means blood is being lost from the gut until proven otherwise. Added weight loss makes colorectal cancer the diagnosis to exclude first.
The Gastroenterological Society of Australia and Therapeutic Guidelines recommend that men and post-menopausal women with iron deficiency anaemia have both colonoscopy and upper endoscopy [VERIFY]. Colonoscopy comes first here because colorectal cancer is the most likely and most dangerous cause in this age group. Both procedures are often done under the same anaesthetic.
A negative faecal immunochemical test does not exclude cancer. The test is designed for screening asymptomatic people, not for investigating a patient who already has anaemia or weight loss. Bleeding from tumours is intermittent, so a single negative sample is not reassuring. The Cancer Council's optimal care pathway lists iron deficiency anaemia as a reason for direct referral to colonoscopy [VERIFY].
Iron replacement will be needed, but giving it before the cause is found can mask the problem and delay the diagnosis of a treatable cancer.
Coeliac serology should also be sent, because coeliac disease is a common cause of iron deficiency in Australia, but it does not replace the need for colonoscopy in this presentation.
Why the other options are wrong
- B
Upper endoscopy is also needed, but colorectal cancer is the most likely cause and colonoscopy comes first.
- C
The blood picture already proves iron deficiency; bone marrow adds nothing.
- D
Repeating a screening test in a symptomatic patient delays diagnosis; a negative FIT does not exclude cancer.
- E
Treating without a cause can hide an underlying malignancy.
High-yield takeaway
Iron deficiency anaemia in a man or post-menopausal woman is a gut lesion until proven otherwise: colonoscopy and gastroscopy, regardless of a negative FIT.
Reference: GESA Clinical Update: Iron Deficiency (and Cancer Council Optimal Care Pathway for Colorectal Cancer) (2022)
Common questions
Does a negative FIT rule out bowel cancer?
No. FIT is a screening test for people without symptoms. Bleeding from tumours is intermittent, so a symptomatic patient needs colonoscopy regardless.
Should upper endoscopy be done too?
Yes. Men and post-menopausal women with iron deficiency anaemia have both colonoscopy and gastroscopy, often at the same sitting.
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