GastroenterologyTier 1Approach to a presentation

Pallor and fatigue

Red flags

Iron deficiency anaemia in a man of any age, or a post-menopausal woman - occult GI malignancy until proven otherwise, requires bidirectional endoscopy
Unintentional weight loss, change in bowel habit, or PR bleeding accompanying fatigue/pallor
Haemodynamic instability (tachycardia, hypotension, postural drop) with severe anaemia - needs urgent assessment/transfusion, not routine outpatient work-up
Fatigue with jaundice/dark urine - hints at a haemolytic rather than deficiency process
Family history of colorectal cancer/polyposis syndrome in a patient with new iron deficiency

Blood loss (the GI-specific concern)

Occult GI malignancy (colorectal, gastric) - the diagnosis that must be actively excluded, especially in higher-risk demographics
Peptic ulcer disease, angiodysplasia, oesophagitis - chronic occult blood loss
Overt but unrecognised loss - haemorrhoids attributed without excluding a more proximal source in an at-risk patient

Malabsorption

Coeliac disease - iron, folate, and B12 malabsorption from proximal small bowel villous atrophy; may present with fatigue/anaemia alone, without GI symptoms
Post-gastrectomy/bariatric surgery - reduced intrinsic factor, reduced acid for iron absorption
Terminal ileal disease/resection (Crohn's) - B12 malabsorption specifically

Chronic disease/other GI-associated mechanisms

Anaemia of chronic disease - IBD, chronic liver disease - hepcidin-mediated iron restriction, distinct from true iron deficiency
Chronic liver disease - macrocytic anaemia, hypersplenism (pancytopenia pattern)
B12/folate deficiency - pernicious anaemia (autoimmune, associated with other autoimmune disease), dietary, or malabsorptive

Bowel habit change, PR bleeding/melaena, abdominal pain, weight loss
Dietary history (vegan/vegetarian - B12 risk), alcohol use, medication (NSAIDs, PPIs long-term - B12 absorption, anticoagulants)
Family history of colorectal cancer, coeliac disease, polyposis syndromes
Menstrual history in women - but do not assume menorrhagia explains iron deficiency in a post-menopausal woman
Symptoms of malabsorption - bloating, steatorrhoea, weight loss despite normal intake

Conjunctival pallor, koilonychia, angular stomatitis, glossitis (iron deficiency signs)
Signs of chronic liver disease if relevant differential
Abdominal examination for masses, organomegaly, lymphadenopathy
Digital rectal examination - often omitted, can reveal a low rectal mass or overt blood
Signs of malabsorption (wasting, oedema from hypoalbuminaemia)

Confirm and characterise the anaemia first

FBE, iron studies (ferritin, transferrin saturation), B12/folate, reticulocyte count, blood film
Low ferritin confirms iron deficiency; note ferritin is an acute phase reactant and can be falsely normal/elevated with concurrent inflammation - interpret alongside transferrin saturation and clinical context

Once iron deficiency confirmed - find the source

Coeliac serology (tissue transglutaminase IgA + total IgA) - check before committing to endoscopy alone, as coeliac disease can coexist with or mimic a GI blood loss picture
Bidirectional endoscopy (gastroscopy + colonoscopy) - the standard work-up for iron deficiency anaemia in men and post-menopausal women, and in premenopausal women where menstrual loss does not adequately explain the degree of deficiency
Faecal occult blood testing has no role in the work-up of confirmed iron deficiency anaemia - a negative result does not exclude a GI source and should not delay endoscopy

B12/folate-driven picture

Anti-intrinsic factor/anti-parietal cell antibodies if pernicious anaemia suspected
Consider terminal ileal imaging/history if Crohn's-related B12 malabsorption suspected

A. Treat the deficiency

Oral iron replacement first-line for iron deficiency; IV iron if intolerant, malabsorptive cause, ongoing losses, or urgent correction needed
B12 replacement (IM initially if deficient, especially if malabsorptive cause) and folate replacement as indicated
Transfuse only if symptomatic/haemodynamically significant anaemia - not based on haemoglobin number alone

B. Treat/investigate the underlying cause - do not stop at correcting the blood count

Endoscopic findings direct management - e.g. polypectomy, ulcer treatment (PPI +/- H. pylori eradication), oncology referral if malignancy found
Coeliac disease - gluten-free diet, dietitian input, monitor serology and nutritional recovery
Continued unexplained iron deficiency despite negative bidirectional endoscopy - consider small bowel imaging (capsule endoscopy) for a small bowel source

Treating iron deficiency anaemia with iron supplements alone without investigating the cause, particularly in men/post-menopausal women
Attributing iron deficiency in a post-menopausal woman to "old menstrual history" without endoscopic work-up
Relying on faecal occult blood testing to decide whether endoscopy is needed once iron deficiency anaemia is already confirmed - it adds nothing at that point
Missing coeliac disease because the patient has no GI symptoms - fatigue/anaemia alone is a recognised presentation
Stopping the work-up once one plausible cause (e.g. haemorrhoids) is found in a higher-risk patient, without excluding a more significant proximal source

1. Iron deficiency in the wrong demographic is a cancer work-up

"A man or a post-menopausal woman with new iron deficiency gets scoped at both ends - I don't stop at 'probably haemorrhoids'."

2. FOBT has already done its job by the time anaemia is confirmed

"Once the iron studies confirm deficiency, a stool test adds nothing - I go straight to endoscopy."

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