Gastroenterology: Investigations

• Endoscopy: Gastroscopy and Colonoscopy | Anticoagulants and Antiplatelets at Endoscopy | Other Endoscopic Tests
• Other tests: GI Imaging | Stool, Breath and Blood Tests
• Common problems: Iron Deficiency Anaemia | Suspected Small Bowel Bleeding | Unintentional Weight Loss
• Nutrition: Malnutrition and Screening | Refeeding Syndrome | Tube Feeding | Parenteral Nutrition | Vitamin and Trace Element Deficiencies
• Intestinal failure: Short Bowel and Intestinal Failure | Stomas | Nutrition Decisions and End of Life
• Revision: Drug Reference Table | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🔬 GI investigations and nutrition are part of everyday ward work: consenting for and preparing patients for endoscopy, managing anticoagulants around procedures, investigating iron deficiency and weight loss, and feeding people safely. Malnutrition affects about 1 in 3 hospital admissions and is often missed.
Your four questions for every patient: Which test answers the question with the least risk? Are anticoagulants, diabetes drugs and kidney function managed safely around the procedure? Is the patient malnourished or at risk of refeeding syndrome? If feeding is needed, what is the safest route - and is it in their best interests?

Gastroscopy and Colonoscopy

Gastroscopy (OGD - oesophago-gastro-duodenoscopy):

• Uses:
  • Dysphagia, dyspepsia with red flags, upper GI bleeding.
  • Iron deficiency anaemia; coeliac biopsies.
  • Barrett's surveillance; varices.
  • Treatment - banding, dilatation, stents, PEG.
• Preparation: Nothing to eat for about 6 hours before; clear fluids up to 2 hours before.
• Sedation: Throat spray alone, or IV sedation (midazolam with or without an opioid).
• Risks: Very low for diagnostic tests (perforation, bleeding, aspiration, sedation reactions, dental damage). Higher with treatment (e.g. dilatation).

Colonoscopy:

• Uses:
  • Change in bowel habit, rectal bleeding, positive FIT.
  • Iron deficiency anaemia.
  • IBD; polyp surveillance; screening.
  • Treatment - polypectomy, haemostasis, stenting.
• Bowel preparation:
  • Low-residue diet for 1–2 days; stop iron tablets about a week before.
  • Polyethylene glycol (PEG) preparations (e.g. Moviprep, Plenvu) are safest.
  • Sodium picosulfate (Picolax) - avoid in CKD, heart failure and frailty (fluid and sodium shifts, hyponatraemia).
  • Avoid phosphate preparations (kidney injury).
  • Diabetes: Adjust insulin and tablets. Withhold SGLT2 inhibitors (risk of DKA during prep).
  • Withhold diuretics and ACE inhibitors on prep day in at-risk patients.
• Risks:
  • Perforation (about 1 in 1,000–3,000, higher with polypectomy).
  • Bleeding after polypectomy (can be delayed by up to 2 weeks).
  • Missed lesions.
  • Sedation reactions.
• Flexible sigmoidoscopy: Examines the rectum and left colon after an enema - used for rectal bleeding in younger people and for acute colitis (safer than full colonoscopy).

Sedation safety:

• Use lower doses in older people.
• Monitor oxygen and BP; give oxygen.
• Reversal agents: flumazenil (benzodiazepines) and naloxone (opioids).
• No driving for 24 hours after sedation.

↑ Back to index

Anticoagulants and Antiplatelets at Endoscopy

BSG/ESGE 2021 guidance balances the risk of bleeding from the procedure against the risk of clotting from stopping the drug.

Low-risk procedures - diagnostic OGD or colonoscopy with biopsies, biliary or pancreatic stenting, diagnostic EUS, capsule endoscopy:

• Continue aspirin and P2Y12 inhibitors (clopidogrel, prasugrel, ticagrelor).
• Warfarin: Continue (check the INR is not above the therapeutic range in the week before).
• DOACs: Omit the dose on the morning of the procedure.

High-risk procedures - polypectomy, ERCP with sphincterotomy, EUS-guided biopsy, PEG, dilatation, endoscopic resection, variceal treatment:

• Aspirin: Continue (except for the highest-risk resections).
• P2Y12 inhibitors:
  • Low thrombotic risk (e.g. more than 12 months after a stent) - stop 7 days before (5 days for ticagrelor); continue aspirin.
  • High thrombotic risk (e.g. a coronary stent within 12 months, or ACS) - discuss with cardiology; consider delaying the procedure.
• Warfarin: Stop 5 days before; check INR is under 1.5.
  • Bridge with LMWH only if the clotting risk is high:
    • Mechanical mitral valve, or a mechanical valve with AF.
    • VTE within the last 3 months.
    • Some thrombophilias.
• DOACs:
  • Last dose at least 48 hours before.
  • Dabigatran with creatinine clearance 30–50 mL/min: 72 hours.
  • No bridging needed.
• Restarting:
  • Warfarin the same evening.
  • DOACs usually 2–3 days after high-risk procedures.
  • P2Y12 inhibitors once haemostasis is secure.

⚠️ Safety Pearl: Never stop antiplatelets in a patient with a recent coronary stent without speaking to cardiology - stent thrombosis is often fatal.

↑ Back to index

Other Endoscopic Tests

• Capsule endoscopy:
  • A swallowed camera pill that images the small bowel.
  • Uses:
    • Suspected small bowel bleeding.
    • Iron deficiency after normal OGD and colonoscopy.
    • Small bowel Crohn's disease.
    • Polyposis syndromes.
  • Risk: Capsule retention at a stricture - use a patency capsule first if a stricture is possible (e.g. Crohn's, NSAID use, previous surgery).
  • Colon capsule is used in some areas as an alternative to colonoscopy.
• Device-assisted enteroscopy (single- or double-balloon): Reaches deep into the small bowel for biopsy and treatment of lesions found on capsule.
• ERCP and EUS: See the Pancreas and Biliary chapter.
• Endoscopic resection: Endoscopic mucosal resection (EMR) and submucosal dissection (ESD) remove large polyps and early cancers without surgery.
• Capsule sponge (Cytosponge): A swallowed sponge on a string collects oesophageal cells - used to detect Barrett's oesophagus.
• Transnasal endoscopy: Thinner scope through the nose; better tolerated without sedation.
• Physiology tests:
  • High-resolution oesophageal manometry (achalasia, motility).
  • 24-hour pH-impedance (reflux).
  • Anorectal manometry (constipation, incontinence).

↑ Back to index

GI Imaging

💡 Clinical Pearl: Check kidney function before IV contrast. In AKI, discuss the risk and benefit with radiology - don't delay a CT that is needed to diagnose a life-threatening condition.

↑ Back to index

Stool, Breath and Blood Tests

• Stool tests:
  • FIT (faecal immunochemical test) - detects human blood. Used for symptomatic triage (10 µg/g or more means urgent referral) and for screening.
  • Faecal calprotectin - bowel inflammation (IBD vs IBS); also raised by NSAIDs, infection and cancer.
  • Faecal elastase - pancreatic exocrine function (under 200 µg/g is low).
  • Culture, microscopy (ova, cysts, parasites), GI PCR panels, C. difficile.
  • H. pylori stool antigen.
  • Faecal alpha-1 antitrypsin - protein-losing enteropathy.
• Breath tests:
  • Urea breath test - H. pylori (stop PPIs for 2 weeks).
  • Hydrogen (and methane) breath tests - lactose intolerance (lactose load) and SIBO (glucose or lactulose load).
• Blood tests:
  • Coeliac serology - IgA tTG with total IgA.
  • Iron studies, B12, folate, vitamin D, zinc, magnesium.
  • Fasting gut hormone profile (gastrin, VIP, glucagon, somatostatin) and chromogranin A - neuroendocrine tumours.
  • Urine 5-HIAA - carcinoid syndrome.
  • Tumour markers: CEA (colorectal follow-up), CA19-9 (pancreas, biliary), AFP (HCC) - for monitoring, not screening.

↑ Back to index

Iron Deficiency Anaemia

Why it matters: Iron deficiency anaemia (IDA) in men and postmenopausal women is a common presentation of GI cancer (especially right-sided colon and gastric cancer).

Confirming iron deficiency (BSG 2021):

• Low ferritin - the single most useful test. Under 15 µg/L confirms deficiency; BSG suggests investigating at under 45 µg/L.
• Ferritin rises with inflammation - use transferrin saturation (under 20%) if ferritin is "normal" but inflammation is present.
• Microcytosis supports it. Consider thalassaemia trait if MCV is very low with a normal ferritin.

Causes:

• Blood loss - GI (cancer, ulcers, angiodysplasia, NSAIDs, aspirin, anticoagulants), menstruation, urinary tract.
• Malabsorption - coeliac disease, atrophic gastritis, H. pylori, gastric surgery.
• Poor diet.
• Pregnancy; blood donation.

Investigation:

• Everyone: Coeliac serology; urinalysis (for haematuria).
• Men and postmenopausal women: Bidirectional endoscopy (OGD and colonoscopy, or CT colonography if frail).
• Premenopausal women: Coeliac serology; endoscopy if aged 50 or over, GI symptoms, a strong family history of colorectal cancer, or IDA that persists despite iron.
• FIT can help triage people with IDA (NICE DG56). However, IDA in men and postmenopausal women usually needs endoscopy even if FIT is low.
• Recurrent IDA after normal endoscopy: capsule endoscopy.
• Consider stopping NSAIDs and reviewing antithrombotics.

Treatment:

• Oral iron - e.g. ferrous sulfate 200 mg once daily (or on alternate days, which is better absorbed and tolerated).
• Expect Hb to rise by about 20 g/L in 3–4 weeks.
• Continue for about 3 months after Hb normalises, to refill stores.
• Side effects: Nausea, constipation, dark stools.
• Vitamin C may help absorption; avoid taking with tea or PPIs if possible.
• IV iron (e.g. ferric carboxymaltose, ferric derisomaltose):
  • If oral iron fails or isn't tolerated.
  • In malabsorption, IBD, CKD, or heart failure.
  • Late pregnancy; before surgery.
  • Watch: Low phosphate (with ferric carboxymaltose); rare hypersensitivity.
• Transfusion only for severe symptomatic anaemia or active bleeding.

↑ Back to index

Suspected Small Bowel Bleeding

• What it is: GI bleeding (overt or iron deficiency) with a normal OGD and colonoscopy (previously called "obscure GI bleeding"). Most sources are in the small bowel.
• Causes:
  • Over 40: Angiodysplasia (the commonest), NSAID ulcers, tumours (GIST, NETs, lymphoma, adenocarcinoma, metastases such as melanoma).
  • Under 40: Crohn's disease, Meckel's diverticulum, tumours, Dieulafoy lesions, polyposis syndromes.
• Approach:
  • Consider repeating OGD and colonoscopy if the first ones were poor quality.
  • Capsule endoscopy (ideally within 2 weeks of the bleed).
  • CT enterography or MR enterography if a tumour or stricture is suspected.
  • CT angiography if bleeding is active.
  • Meckel's scan in young people.
  • Enteroscopy to treat lesions.
• Meckel's diverticulum ("rule of 2s"):
  • About 2% of people; about 2 feet from the ileocaecal valve; about 2 inches long.
  • May contain gastric tissue - painless bleeding in children and young adults.

↑ Back to index

Unintentional Weight Loss

What counts: Loss of more than 5% of body weight over 6–12 months without trying. Weigh the patient and look at previous records.

Causes - often more than one, especially in older people:

• Cancer (GI, lung, pancreas, lymphoma, others).
• GI disease - malabsorption, IBD, peptic ulcer, dysphagia, chronic pancreatitis, mesenteric ischaemia.
• Endocrine - hyperthyroidism, uncontrolled diabetes, Addison's disease.
• Chronic organ failure - heart failure (cardiac cachexia), COPD, CKD, liver disease.
• Infection - TB, HIV, endocarditis.
• Psychiatric - depression, eating disorders, dementia.
• Drugs - metformin, GLP-1 receptor agonists, SSRIs, digoxin, levothyroxine excess; alcohol and drugs of misuse.
• Social - poverty, isolation, poor dentition, inability to shop or cook.

First tests:

• FBC, U&E, LFTs, calcium, glucose and HbA1c, TFTs, CRP or ESR.
• Ferritin; coeliac serology.
• Urinalysis.
• Chest X-ray.
• FIT.
• Consider HIV testing; PSA after discussion in men.
• Follow NICE NG12 pathways for specific symptoms. For non-specific symptoms with concern for cancer, Rapid Diagnostic Centres (non-specific symptoms pathways) offer fast-track assessment.

↑ Back to index

Malnutrition and Screening

Definition (NICE CG32) - malnourished if:

• BMI under 18.5, or
• Unintentional weight loss over 10% in 3–6 months, or
• BMI under 20 with weight loss over 5% in 3–6 months.

At risk if:

• The patient has eaten little or nothing for more than 5 days, or is likely to.
• Absorption is poor.
• Losses are high (vomiting, fistulas, stomas).
• Needs are increased (sepsis, burns).

Screening - MUST (Malnutrition Universal Screening Tool), on admission and weekly in hospital:

• BMI score: Over 20 = 0; 18.5–20 = 1; under 18.5 = 2.
• Weight loss score (in 3–6 months): Under 5% = 0; 5–10% = 1; over 10% = 2.
• Acute disease effect (acutely ill and no intake for more than 5 days) = 2.
• Total: 0 = low risk; 1 = medium (monitor intake); 2 or more = high (dietitian referral and a nutrition plan).

Management:

• Food first: Fortified food, snacks, help with eating (red trays, protected mealtimes), treat mouth and dental problems.
• Oral nutritional supplements ("sip feeds").
• Dietitian review.
• Tube feeding if the patient can't meet needs by mouth and the gut works.
• Parenteral nutrition only if the gut doesn't work or can't be accessed.
• Treat underlying causes; review drugs that suppress appetite.
• Sarcopenia in older people: protein (1–1.2 g/kg/day or more) plus resistance exercise.

↑ Back to index

Refeeding Syndrome

What it is: Dangerous shifts in fluid and electrolytes when a starved person starts eating or being fed. Insulin surges drive phosphate, potassium and magnesium into cells, and use up thiamine.

Consequences:

• Arrhythmias; heart failure.
• Respiratory failure.
• Seizures; confusion.
• Wernicke's encephalopathy.
• Fluid overload.
• Death.

High risk (NICE CG32) - one or more of:

• BMI under 16.
• Unintentional weight loss over 15% in 3–6 months.
• Little or no intake for more than 10 days.
• Low potassium, phosphate or magnesium before feeding.

Or two or more of:

• BMI under 18.5.
• Weight loss over 10% in 3–6 months.
• Little intake for more than 5 days.
• Alcohol misuse, or drugs such as insulin, chemotherapy, antacids or diuretics.

Typical at-risk groups:

• Anorexia nervosa.
• Alcohol dependence.
• Cancer.
• Older people after a long illness or falls with long lie.
• Prolonged vomiting.
• After bariatric surgery.

Prevention and treatment:

• Start feeding slowly: No more than 10 kcal/kg/day (5 kcal/kg/day in extreme cases, e.g. BMI under 14 or negligible intake for over 15 days), increasing over 4–7 days.
• Thiamine before and during feeding - e.g. oral thiamine 200–300 mg daily, or IV Pabrinex - plus vitamin B compound strong and a multivitamin.
• Replace electrolytes (unless levels are high):
  • Potassium 2–4 mmol/kg/day.
  • Phosphate 0.3–0.6 mmol/kg/day.
  • Magnesium (0.2 mmol/kg/day IV or 0.4 oral).
• Monitor potassium, phosphate, magnesium, glucose and fluid balance daily for the first week, then less often.
• Don't delay feeding while correcting levels - correct alongside.

↑ Back to index

Tube Feeding

Nasogastric (NG) tubes - for short-term feeding (up to about 4 weeks):

• Checking position before every use (NHS Improvement guidance):
  • Aspirate with pH 5.5 or less.
  • If no aspirate or pH over 5.5: chest X-ray, interpreted by a competent person.
  • Never use the "whoosh" test, litmus paper or the appearance of the aspirate.
  • Feeding through a misplaced tube in the lung is a never event.
• Nasal bridle for patients who repeatedly pull tubes out.
• Nasojejunal tubes - for gastric outlet problems or severe gastroparesis, and sometimes in pancreatitis.

Gastrostomy (PEG or RIG) - for longer-term feeding (more than about 4 weeks):

• Good indications:
  • Stroke with dysphagia that hasn't recovered after 2–4 weeks.
  • Motor neurone disease (place early, before breathing worsens).
  • Head and neck cancer.
  • Some neurological disabilities.
• Advanced dementia: Tube feeding does not prolong life, prevent aspiration or improve comfort. Careful hand feeding is preferred.
• Risks:
  • Significant 30-day mortality in frail patients - choose carefully.
  • Infection at the site; peritonitis; bleeding.
  • Buried bumper - the internal disc grows into the stomach wall. Prevent by advancing and rotating the tube weekly once healed.
  • Tube blockage; leakage.
  • Aspiration still happens (from mouth secretions and reflux).
• RIG (radiologically inserted gastrostomy) - when endoscopy isn't possible (e.g. obstructing head and neck cancer).
• Dislodged tube: The tract can close within hours - urgent replacement or a catheter to keep it open.

Complications of tube feeding:

• Diarrhoea - check for C. difficile, drugs (sorbitol in liquid medicines, antibiotics) and feed rate.
• Aspiration - sit at 30–45 degrees.
• Refeeding syndrome.
• Hyperglycaemia.
• Electrolyte problems.

Giving medicines through tubes: Ask a pharmacist. Don't crush modified-release or enteric-coated tablets. Flush before and after. Phenytoin and levothyroxine absorption is altered by feeds.

↑ Back to index

Parenteral Nutrition

• What it is: Nutrition given intravenously - "if the gut works, use it" - so PN is for when it doesn't, or can't be accessed safely.
• Indications:
  • Intestinal failure - short bowel, obstruction, prolonged ileus.
  • High-output fistulas.
  • Severe mucositis.
  • Severe malabsorption.
  • Some cases of severe pancreatitis where enteral feeding fails.
• Access:
  • Central venous line (PICC or tunnelled line), with a dedicated lumen for PN.
  • Peripheral PN for short periods only.
• Complications:
  • Line infection (catheter-related bloodstream infection) - fever or rigors when PN is connected; blood cultures from the line and peripherally.
  • Line thrombosis; air embolism; line occlusion.
  • Metabolic: Refeeding syndrome, hyperglycaemia, electrolyte imbalance, fluid overload.
  • Liver disease (intestinal failure-associated liver disease) - cholestasis, fatty liver.
  • Metabolic bone disease; gallstones.
• Monitoring: Daily weight, fluid balance and glucose; electrolytes (including phosphate and magnesium) daily at first; LFTs, triglycerides, trace elements and vitamins periodically.
• Run by a nutrition support team. Home PN is managed by specialist intestinal failure units.

↑ Back to index

Vitamin and Trace Element Deficiencies

⚠️ Safety Pearl: Give thiamine before glucose in any malnourished or alcohol-dependent patient - glucose can precipitate Wernicke's encephalopathy.

↑ Back to index

Short Bowel and Intestinal Failure

Intestinal failure: The gut can't absorb enough nutrients or fluid, so IV support is needed.

• Type 1 - short-term (e.g. ileus after surgery).
• Type 2 - prolonged, in unwell patients (e.g. after abdominal catastrophe, fistulas) - needs a specialist unit.
• Type 3 - chronic, stable, needing home parenteral support.

Short bowel syndrome:

• Causes: Typically less than 200 cm of small bowel remaining after resections (Crohn's disease, mesenteric ischaemia, volvulus, radiation, trauma).
• Two main types:
  • Jejunostomy (no colon) - huge fluid and sodium losses, dehydration, low magnesium.
  • Small bowel joined to colon - fewer fluid problems, but oxalate kidney stones, gallstones, bile acid diarrhoea and D-lactic acidosis (confusion after carbohydrate loads).
• Managing a high-output jejunostomy (output over about 1.5–2 L/day):
  • Restrict hypotonic fluids (water, tea, juice) to about 500 mL–1 L a day - these increase losses.
  • Oral rehydration solution - St Mark's solution (sodium about 90 mmol/L), about 1 L a day.
  • Loperamide in high doses (taken 30–60 minutes before meals; can be opened from capsules), with codeine if needed.
  • PPI or H2 blocker to reduce gastric secretions (especially early on).
  • Salt food liberally; separate drinks from meals.
  • Replace magnesium.
  • Specialist options: teduglutide (a GLP-2 analogue that helps the bowel adapt), IV fluids or PN.
• Monitoring:
  • Weight.
  • Urine output and urine sodium (aim over 20 mmol/L).
  • U&E, magnesium.
  • B12, fat-soluble vitamins, zinc, bone health.
• Intestinal transplant is very rare.

↑ Back to index

Stomas

Types:

• End stoma - often permanent.
• Loop stoma - temporary; diverts stool to protect a join further down, then reversed.
• Urostomy (ileal conduit) - for urine after bladder removal.

Complications:

• High output (over 1.5 L/day) - dehydration, AKI, low sodium and magnesium. Manage as for short bowel and look for causes (infection, C. difficile, drug changes, obstruction, recurrent disease).
• Early: Ischaemia (dark or black stoma - urgent surgical review); retraction; skin irritation.
• Late: Parastomal hernia (common); prolapse; stenosis; obstruction (food bolus); skin problems (pyoderma gangrenosum in IBD).
• Drugs: Modified-release tablets may pass unabsorbed through an ileostomy.
• Psychological and body-image problems. Stoma nurses are essential before and after surgery.

↑ Back to index

Nutrition Decisions and End of Life

• Clinically assisted nutrition and hydration (tube feeding, PN, IV fluids) is a medical treatment, not basic care. It should only be given if it is likely to benefit the patient. Oral food and drink offered by mouth is basic care and should always be offered.
• Patients with capacity can refuse any treatment, including tube feeding.
• Patients without capacity (Mental Capacity Act 2005):
  • Decide in their best interests.
  • Check for an advance decision or a lasting power of attorney for health and welfare.
  • Involve family and the multidisciplinary team.
  • Use an IMCA if there is no one to consult.
• Eating and drinking with acknowledged risks (RCP guidance): When dysphagia can't be made safe and tube feeding is not in the patient's interests (e.g. advanced dementia, end of life), the patient continues to eat and drink for comfort. Use the safest textures and positioning; document the decision and share it.
• Time-limited trials of feeding with agreed review points are often helpful when benefit is uncertain (e.g. after stroke).
• At the end of life: Thirst and hunger are uncommon. Mouth care matters more than fluids. Subcutaneous fluids can be used if they help symptoms.
• Follow GMC guidance on treatment and care towards the end of life, and BMA/RCP guidance on clinically assisted nutrition and hydration.

↑ Back to index

Drug Reference Table

↑ Back to index

Spot the Diagnosis

↑ Back to index

Exam-style Scenarios

1. A 72-year-old on apixaban for AF needs a colonoscopy with removal of a 25 mm polyp. Creatinine clearance is 60 mL/min.
Answer: High-risk procedure.

• Last dose of apixaban at least 48 hours before; no bridging.
• Restart 2–3 days after the procedure if haemostasis is secure.
• Use a PEG-based bowel prep.

2. A 66-year-old woman has Hb 98 g/L, MCV 74 fL and ferritin 8 µg/L. She has no GI symptoms.
Answer: Iron deficiency anaemia in a postmenopausal woman.

• Coeliac serology and urinalysis.
• OGD and colonoscopy (urgent pathway).
• Ferrous sulfate 200 mg daily or on alternate days; check Hb in 3–4 weeks.
• Capsule endoscopy if recurrent after normal tests.

3. A 45-year-old with alcohol dependence (BMI 16, eating little for 2 weeks) is admitted. NG feeding is planned.
Answer: High risk of refeeding syndrome.