Synopsis
Localise malabsorption to luminal digestion, intestinal mucosa, bile acid handling, lymphatic transport or reduced absorptive surface; test for coeliac disease and pancreatic insufficiency correctly; and replace deficits without obscuring the cause.
- Steatorrhoea, chronic diarrhoea, weight loss, bloating, anaemia, oedema, bruising, neuropathy or bone disease may be the presenting phenotype; absence of obvious stool fat does not exclude malabsorption.
- Classify mechanisms: impaired intraluminal digestion, mucosal disease, reduced small-bowel surface, bile acid diarrhoea, lymphatic obstruction or mixed postoperative causes.
- For coeliac testing, the patient must be eating gluten; check total IgA with IgA tissue transglutaminase and use appropriate IgG-based testing in IgA deficiency.
- Do not advise a gluten-free diet before the diagnostic pathway is complete unless a specialist has agreed an alternative, because serology and histology can normalise.
- Faecal elastase supports pancreatic exocrine insufficiency but watery diarrhoea can dilute the sample and cause a falsely low result.
- Test for bile acid diarrhoea with SeHCAT or an accepted alternative where available rather than assuming every post-cholecystectomy or ileal symptom is IBS.
- Replace iron, folate, B12, vitamin D, calcium and other deficits according to measured need, but check B12 before giving folic acid alone.
- Severe depletion, tetany, arrhythmia, neurological deficit or high refeeding risk requires urgent correction and specialist nutrition support.
Key red flags
Steatorrhoea, weight loss, diabetes, recurrent pancreatitis, pancreatic surgery or chronic epigastric pain suggests inadequate enzyme delivery; pancreatic cancer must be considered with new symptoms or jaundice.
Arrhythmia or tetany from electrolyte disturbance, confusion, ophthalmoplegia, profound anaemia, spinal-cord or peripheral nerve signs, or pathological fracture requires urgent correction and cause assessment.
Investigation priorities
Measure total IgA and IgA tTG, with EMA for weakly positive results and IgG-based testing when IgA deficient according to the current pathway.
Management branches
Chronic diarrhoea, steatorrhoea, weight loss or unexplained nutrient deficiency suggests impaired absorption.
- Confirm stool and weight phenotype, review diet, surgery, pancreas, ileum, medicines, travel and immune state, and assess dehydration or severe deficiency.
- Screen for coeliac disease while gluten is still consumed, inflammation and common deficiencies; add faecal elastase and bile acid testing according to phenotype.
- Use endoscopy and imaging to investigate mucosal disease, obstruction, pancreatic pathology or malignancy rather than labelling unexplained symptoms functional.
- Treat urgent depletion in parallel but retain baseline samples where safe so replacement does not erase diagnostic evidence.