Key Facts

Malabsorption encompasses a wide range of conditions that impair nutrient absorption from the small intestine. Identifying the specific cause is essential, as treatment is often highly effective. A systematic approach based on the pattern of nutrient deficiency helps localise the site and cause.

Epidemiology

Coeliac disease affects ~1% of UK population (many undiagnosed). Pancreatic exocrine insufficiency complicates ~85% of chronic pancreatitis. Crohn's disease prevalence ~150 per 100,000 in UK. Short bowel syndrome affects ~50 per million.

Aetiology

• Mucosal disease: coeliac disease, Crohn's disease, tropical sprue, Whipple disease, radiation enteropathy, giardiasis
• Pancreatic insufficiency: chronic pancreatitis, cystic fibrosis, pancreatic cancer
• Bile salt deficiency: primary biliary cholangitis, bile acid malabsorption, ileal resection/disease
• Structural/surgical: short bowel syndrome, gastric bypass, blind loop syndrome
• Other: small bowel bacterial overgrowth, lymphangiectasia, systemic sclerosis, amyloidosis

Pathophysiology

Nutrient absorption requires: (1) adequate luminal digestion (pancreatic enzymes + bile salts), (2) intact mucosal surface area, (3) functional enterocyte transport. Malabsorption occurs when any of these is disrupted. Fat malabsorption is most clinically obvious (steatorrhoea). Different nutrients are absorbed at specific sites — the pattern of deficiency helps localise the lesion: duodenum (iron, calcium, folate), jejunum (sugars, amino acids, fat-soluble vitamins), terminal ileum (B12, bile salts).

General Features

• Chronic diarrhoea (often steatorrhoea)
• Weight loss despite adequate intake
• Abdominal bloating and flatulence
• Fatigue and lethargy

Specific Deficiency Signs

• Iron deficiency: pallor, koilonychia, glossitis, angular stomatitis
• B12/folate deficiency: megaloblastic anaemia, glossitis, peripheral neuropathy (B12)
• Calcium/vitamin D: osteomalacia, osteoporosis, tetany, muscle weakness
• Vitamin K: easy bruising, prolonged PT
• Vitamin A: night blindness, dry eyes
• Zinc: acrodermatitis, poor wound healing
• Protein: oedema, muscle wasting

Red Flags

• Significant unintentional weight loss (>5% in 3 months)
• Iron deficiency anaemia in postmenopausal women or men (exclude GI malignancy)
• Steatorrhoea with back pain (pancreatic cancer)
• Dermatitis herpetiformis (coeliac — blistering rash on extensor surfaces)

Bedside

• Weight and BMI: document trend
• Stool inspection: steatorrhoea (pale, bulky, offensive)

Bloods

• FBC + film: microcytic (iron) or macrocytic (B12/folate) anaemia; dimorphic picture in combined deficiency
• Iron studies: low ferritin, low iron, raised TIBC
• B12 and folate: pattern helps localise (see above)
• Calcium, phosphate, vitamin D, PTH: bone metabolism
• Albumin: low in protein malabsorption
• LFTs: ALP raised in osteomalacia
• Clotting (INR): prolonged in vitamin K deficiency
• tTG-IgA + total IgA: coeliac screening (check IgA level as ~2-3% of coeliac patients are IgA deficient)
• CRP/ESR: Crohn's disease
• Zinc, magnesium, vitamin A/E: if severe malabsorption

Special Tests

• Faecal elastase: <200 μg/g = pancreatic exocrine insufficiency
• SeHCAT scan: bile acid malabsorption (<15% retention at 7 days = abnormal; <5% = severe)
• Glucose hydrogen breath test: SIBO
• OGD + duodenal biopsies: coeliac disease (Marsh classification), Whipple disease, giardiasis
• Colonoscopy + terminal ileum biopsies: Crohn's disease
• MRI enterography: small bowel Crohn's disease
• CT pancreas: chronic pancreatitis (calcification)
• DEXA scan: osteoporosis screening in coeliac/chronic malabsorption

Non-pharmacological

• Dietary assessment: dietitian involvement essential
• Gluten-free diet: lifelong for coeliac disease (NICE NG20)
• Nutritional supplementation: iron, B12 (IM if ileal disease), folate, calcium, vitamin D as indicated
• Medium-chain triglyceride (MCT) diet: for lymphangiectasia and severe fat malabsorption

Pharmacological

• Pancreatic enzyme replacement (PERT): Creon 25,000-50,000 units lipase per meal + 10,000-25,000 per snack (titrate to steatorrhoea); take with/just before food; combine with PPI if suboptimal response
• Bile acid sequestrant: cholestyramine 4 g QDS for bile acid malabsorption; colesevelam 625 mg (1-3 tabs BD) as alternative
• Antibiotics for SIBO: cyclical antibiotics (see SIBO entry)
• Treat underlying cause: mesalazine/biologics for Crohn's, antihelminthics for parasites
• B12 replacement: hydroxocobalamin 1 mg IM every 3 months (if terminal ileum disease/resection)
• Iron replacement: ferrous sulphate 200 mg BD-TDS (or IV iron if oral intolerant/malabsorbed)

Surgical/Interventional

• Crohn's stricturoplasty/resection if obstructive
• Small bowel transplant for short bowel syndrome (rare)

Referral Criteria

• Gastroenterology: all suspected malabsorption for investigation
• Dietitian: all confirmed malabsorption
• Coeliac disease: NICE NG20 pathway
• Haematology: severe/refractory anaemia

Prognosis depends on underlying cause. Coeliac disease: excellent with strict gluten-free diet; small increased lymphoma risk (EATL). Pancreatic insufficiency: well-controlled with PERT in most cases. Crohn's-related: depends on disease activity and extent of resection. Short bowel syndrome: may require long-term TPN; intestinal adaptation improves over 1-2 years. Untreated malabsorption leads to progressive nutritional deficiency and complications (osteoporosis, anaemia, neuropathy).

Nutrient Absorption Sites

Marsh Classification (Coeliac Disease)