Make a diagnosis of IBS if abdominal pain:

• Relieved by defecation and/or

• Altered stool frequency (increased/decreased) and/or

• Altered stool form (hard, lumpy, loose, or watery)

AND at least two of the following:

1. Altered stool passage (straining, urgency, or incomplete evacuation).

2. Abdominal bloating

3. Symptoms worsened by eating

4. Passage of rectal mucus

AND Alternative conditions with similar symptoms have been excluded.

Rome IV: sub-typing IBS by predominant stool pattern

1. IBS with constipation (IBS-C): hard or lumpy stools for ≥25% of bowel movements and loose (mushy) or watery stools for ≤25% of bowel movements.

2. IBS with diarrhoea (IBS-D): loose (mushy) or watery stools for ≥25% of bowel movements and hard or lumpy stool for ≤25% of bowel movements.

3. Mixed IBS (IBS-M): hard or lumpy stools for ≤25% of bowel movements and loose (mushy) or watery stools for ≤25% of bowel movements.

4. Unspecified IBS: insufficient abnormality of stool consistency to meet criteria for IBS-C, IBS-D, or IBS-M.

History

• Type and severity of symptoms
  Abdominal pain, bloating, change in bowel habit,
  Lethargy, nausea, back pain, headache,
  Bladder symptoms (such as nocturia, urgency, and incomplete emptying) Dyspareunia
  Faecal incontinence

• Impact on daily functioning (home, work, emotional)

• Diet: fibre intake, food triggers (such as alcohol, caffeine, spicy and fatty food, lactose-containing foods, or fructose-containing foods)

• Food diary (to identify triggers)

• General physical health and activity

• Symptoms of stress, anxiety, or depression

• Family history of bowel cancer, coeliac, IBD, IBS

Red Flags

Symptoms

• Fever, malaise, anorexia

• Weight loss

• Rectal bleeding

• Blood-stained diarrhoea

• Nocturnal defecation

• Fixed location severe abdominal pain (IBS normally has variable quadrant abdominal pain)

• Back pain, jaundice, new-onset diabetes and CIBH/weight loss

• Dysphagia, upper abdominal pain, reflux, dyspepsia, haematemesis

Signs

• Jaundice, Clubbing

• Abdominal or rectal mass

• Abdominal tenderness, hepatomegaly, splenomegaly, ascites

• Extra-intestinal manifestations, including abnormalities of the joints, eyes, liver, and skin

Investigations

• Iron-deficiency anaemia

• Raised platelet count

• Jaundice

• New-onset diabetes

Examination

• Check the weight, calculate the body mass index (BMI), and assess for unintended or unexplained weight loss

• Palpate the abdomen for signs of tenderness or masses

• Perform a rectal examination, to exclude perianal or rectal pathology

Investigations to exclude alternative diagnosis

• FBC

• Ferritin, B12, folate, Vitamin D

• UEs, LFTs, Calcium

• TFTs

• ESR, CRP

• Coeliac: Anti-TTG antibodies

• CA-125 if female age>40y

• Stool: Faecal calprotectin, FIT (faecal occult blood)

• (Stool examination positive for ova and parasites or stool antigen detection positive for G lamblia)

Differential diagnosis

• Malignancy (colorectal cancer, small bowel cancer, lymphoma, ovarian)

• Coeliac disease and non-coeliac gluten intolerance

• Inflammatory Bowel Disease (Crohn’s, UC)

• Diverticular disease

• Pancreatic exocrine insufficiency from chronic pancreatitis, cystic fibrosis, obstructive pancreatic tumours, coeliac disease, Zollinger-Ellison syndrome, and gastro-intestinal or pancreatic surgical resection [faecal elastase test]

• Gallstones

• GORD/Peptic ulcer disease

• Thyroid disease

• Small intestinal bacterial overgrowth- abdominal bloating and diarrhoea [hydrogen breath test]

• Lactose intolerance [hydrogen breath test]

• Bile acid malabsorption- diarrhoea
  [reduced serum fibroblast growth factor 19, elevated 48hr stool collection for total bile acids, less than 15% retained 23-seleno-25-homotauraocholic acid SeHCAT test one week after ingestion, empiric trial of bile acid binder like colestyramine or colesevelam in IBS-chronic diarrhoea]

• Microscopic colitis

Management

1. Lifestyle
   Regular meals with a healthy, balanced diet
   Adjust their fibre intake according to symptoms (discourage insoluble fibre such as bran).
   Drinking an adequate fluid intake
   Avoid excess alcohol, fizzy drinks, artificial sweetener, restrict tea/coffee to 3 cups per day
   Encouraging regular physical activity and weight management

2. Probiotic supplements (DAILY, at least 4w trial) Bifidobacterium infantis

3. Predominant abdominal pain:
   Antispasmodic mebeverine, hyoscine
   Peppermint oil as drops or enteric coated sustained release tablets
   Low-dose TCA Amitriptyline 10mg-30mg at night
   Selective serotonin reuptake inhibitor (SSRI), such as citalopram or paroxetine

4. Predominant diarrhoea/bloating:
   Reduce insoluble fibre (wholemeal, high-fibre flour, bran, whole grains such as brown rice)
   Loperamide given after a loose stool

5. Predominant constipation:
   Increase soluble fibre: oats, linseed
   Increase soluble fibre: Ispaghula husk bd; Bisacodyl 10-20mg at night; Movicol; Docusate
   No response after 6 months: Linaclotide or Prucalopride (short term trial with f/up to check effectiveness)

6. Exclusion diets, such as low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet. 
   AVOID High FODMAP-foods: fruits (apples, cherries, peaches, and nectarines); artificial sweeteners; most lactose-containing foods; legumes; some green vegetables (broccoli, Brussels sprouts, cabbage, and peas).

7. Specialist gastroenterological referral

8. Hypnotherapy and CBT