A
Aminosalicylates (5-ASA)
A class of anti-inflammatory drugs used to treat mild-to-moderate ulcerative colitis. Examples include mesalazine (Asacol, Salofalk) and sulfasalazine. They work locally in the gut lining rather than suppressing the whole immune system. Not usually effective in Crohn's disease.
Anastomosis
A surgical join between two sections of bowel after a portion has been removed. The quality and healing of this join is critical to surgical outcomes in IBD. An anastomotic leak is a serious complication.
B
Biologic / Biological therapy
A class of medications made from living cells that target specific proteins in the inflammatory process. Common biologics in IBD include infliximab (Remicade), adalimumab (Humira), vedolizumab (Entyvio), and ustekinumab (Stelara). Given by injection or IV infusion.
Bowel prep
A strong laxative solution taken the day before a colonoscopy to completely empty the bowel. Usually involves a restricted diet the day before and drinking 1–2 litres of prep solution. Unpleasant but essential for a clear view.
Bristol Stool Scale
A medical classification of stool consistency from Type 1 (hard lumps, constipation) to Type 7 (entirely liquid, diarrhoea). Types 3 and 4 are considered normal. Used in IBD to track bowel habits objectively. Used in GutTrack™ daily check-in.
C
Calprotectin (faecal)
A protein released by white blood cells that migrate to sites of gut inflammation. Measured in a stool sample. A raised level (above 50–250 μg/g depending on lab) indicates gut inflammation. More gut-specific than CRP — you can have a normal CRP but elevated calprotectin.
CDAI (Crohn's Disease Activity Index)
A scoring system used to measure Crohn's disease activity. Based on symptoms over 7 days including stool frequency, pain, general wellbeing, and other factors. A score under 150 indicates remission. Rarely used in routine clinical practice — HBI is more common.
Colonoscopy
An endoscopic procedure where a flexible camera is passed through the rectum to examine the entire large bowel and often the terminal ileum. Used to diagnose IBD, assess disease activity, take biopsies, and monitor for dysplasia. Usually done under sedation.
Corticosteroids
Powerful anti-inflammatory drugs used to rapidly control IBD flares. Examples include prednisolone and budesonide. Not suitable for long-term use due to side effects including bone density loss and adrenal suppression. Used to induce remission, not maintain it.
CRP (C-Reactive Protein)
A protein produced by the liver in response to inflammation. Normal is under 10 mg/L. A raised CRP alongside IBD symptoms suggests active inflammation. Can be normal even with mild gut inflammation — calprotectin is more sensitive.
D
Dysplasia
Abnormal cell changes found on biopsy that may indicate an increased risk of colorectal cancer. Can be low-grade or high-grade. Don't panic at this word — it's what the surveillance colonoscopy programme is designed to catch early, when it's most treatable.
E
Enteral nutrition
A liquid nutritional formula used as an alternative or supplement to food, either drunk or delivered via a nasogastric (NG) tube. Used in Crohn's disease — particularly in children — as a primary treatment to induce remission. Also called exclusive enteral nutrition (EEN).
Extraintestinal manifestation
IBD symptoms or complications that occur outside the digestive tract. Includes joint pain (arthritis), skin conditions (erythema nodosum, pyoderma gangrenosum), eye inflammation (episcleritis, uveitis), and bone density loss. Affects up to 50% of IBD patients at some point.
F
Fistula
An abnormal tunnel connecting two organs or an organ to the skin surface, formed when inflammation burrows through the gut wall. More common in Crohn's than UC. Can connect bowel to skin (enterocutaneous), bowel to bladder (enterovesical), or between bowel loops. Perianal fistulas are particularly common in Crohn's.
Flare / Flare-up
A period of active IBD symptoms after a period of remission or reduced activity. Can range from mild (increased trips, mild discomfort) to severe (significant bleeding, fever, hospitalisation). Flares don't always have an obvious trigger.
FODMAP
Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols — types of carbohydrates that are poorly absorbed and fermented in the gut. A low-FODMAP diet is used in IBS and sometimes IBD to reduce symptoms. Not a cure for IBD, but can reduce functional symptoms alongside treatment.
H
HBI (Harvey-Bradshaw Index)
A simplified scoring system for Crohn's disease activity. Scores general wellbeing, abdominal pain, number of liquid stools per day, abdominal mass, and complications. A score under 5 suggests remission. Used in GutTrack™'s clinical scores section.
I
Immunomodulator
Drugs that modify the immune system to reduce IBD activity. Examples include azathioprine, mercaptopurine (6-MP), and methotrexate. Take 3–6 months to reach full effect. Regular blood monitoring required.
Infusion
Delivery of medication directly into the bloodstream via a drip (IV cannula), usually at a hospital day unit. Some biologics (infliximab, vedolizumab) are given this way. Typically takes 2–3 hours. Usually every 6–8 weeks once stabilised.
J
JAK inhibitor
A newer class of IBD medication that blocks JAK-STAT signalling pathways involved in immune activation. Unlike biologics, they can be taken as tablets. Examples include tofacitinib (Xeljanz) and upadacitinib (Rinvoq). Strong evidence in UC; growing evidence in Crohn's.
L
Leaky gut (intestinal permeability)
Increased permeability of the gut lining, allowing bacteria and food antigens to cross into tissue where they trigger immune responses. IBD disrupts tight junctions between gut cells, increasing permeability. Not a diagnosis in itself, but a mechanism relevant to IBD inflammation.
M
Mayo Score
A scoring system for ulcerative colitis disease activity. Based on stool frequency, rectal bleeding, endoscopy findings, and physician assessment. A score of 0–1 indicates remission. The endoscopic Mayo score (0–3) is often used separately to assess mucosal healing.
Mucosa / Mucosal healing
The mucosa is the inner lining of the digestive tract. Mucosal healing — where the lining returns to a normal appearance on endoscopy — is now a key treatment goal in IBD, associated with sustained remission. You can feel well without full mucosal healing.
P
Perianal Crohn's
Crohn's disease affecting the area around the anus, including fistulas, abscesses, skin tags, and fissures. Affects around 25% of people with Crohn's disease. Often requires specialist management from both gastroenterology and colorectal surgery.
Primary Sclerosing Cholangitis (PSC)
A liver condition associated with IBD, particularly UC, where the bile ducts become inflamed and scarred. Affects around 5% of UC patients. Requires monitoring by hepatology and increases colorectal cancer surveillance frequency.
R
Remission
A period where IBD symptoms are absent or minimal and disease activity is low or undetectable. Clinical remission means few or no symptoms. Endoscopic remission means the gut lining looks normal on scope. Remission is managed, not cured — most people need ongoing medication to maintain it.
Resection
Surgical removal of a diseased section of bowel. Common in Crohn's disease where a strictured or heavily affected segment is removed. Does not cure Crohn's — inflammation can recur at the surgical join.
S
SCCAI (Simple Clinical Colitis Activity Index)
A scoring tool for ulcerative colitis activity based on bowel frequency (day and night), urgency, blood in stool, general wellbeing, and extraintestinal features. A score under 2.5 suggests remission. Used in GutTrack™'s clinical scores section.
Stricture
A narrowing of the bowel caused by scar tissue from repeated inflammation. Can cause pain, bloating, and obstruction. Common in Crohn's. Managed with endoscopic dilation or, if severe, surgery.
T
Terminal ileum
The final section of the small intestine, just before it joins the large bowel. One of the most commonly affected sites in Crohn's disease. Responsible for absorbing vitamin B12 and bile salts — damage here can cause B12 deficiency.
Thiopurine metabolites
Blood tests that measure how your body is processing azathioprine or mercaptopurine. 6-TGN and 6-MMP levels tell your team whether your dose is adequate or needs adjusting. Under-dosing is common and results in inadequate disease control.
Tight junctions
Protein complexes that seal adjacent cells in the gut lining together, forming the barrier between gut contents and the bloodstream. IBD inflammation disrupts these, increasing gut permeability. Supporting tight junction integrity is why certain nutrients like zinc and gelatine are relevant in IBD.
U
Ulcerative colitis (UC)
A form of IBD affecting the large intestine and rectum. Inflammation is continuous from the rectum upward and confined to the inner lining. Common symptoms include bloody diarrhoea, urgency, and cramping. Affects the large bowel only — unlike Crohn's which can affect anywhere.
