Reasoning GP · Algorithm · 1-page summary
Anal pain in primary care
For: adults with new anal pain. Not for: painless rectal bleeding (rectal bleeding algorithm), a painless lump (anal lumps), itch alone (anal itchiness); children (constipation (child) protocol, paediatric assessment).
Core rule: a perianal abscess needs same-day drainage, not antibiotics alone; and always examine — never label pain or bleeding as fissure or piles until a mass, ulcer or sepsis is excluded.
0Stop — call 999 now
- Any one of: rapidly spreading perianal/perineal redness or swelling, pain out of proportion to the signs, skin discoloration, crepitus, or systemically unwell → suspected Fournier's gangrene → 999. Do not wait for crepitus (a late sign). Diabetes and immunocompromise raise risk; never delay for antibiotics.
- Rectal trauma with sudden severe abdominal pain, peritonism or systemically unwell (possible perforation) → 999.
1Triage — the pain pattern
| Pattern | Think |
|---|---|
| Sharp on defecation | Burning minutes–hours after; blood on paper → fissure |
| Constant, throbbing | Tender swelling, worse sitting, ± fever → abscess (block 2) |
| Sudden, acute lump | Tender blue-black lump at the margin → thrombosed external pile |
| Fleeting, at night | Seconds to minutes, normal examination → proctalgia fugax (exclusion) |
| Discharge + tenesmus | Anal sex → STI proctitis; blood mixed in stool → cancer / IBD |
2Screen — serious causes
- Tender perianal swelling, ± fever → abscess → Same-day surgical drainage (phone the registrar); never drain in practice.
- Rectal trauma or foreign body → Same-day hospital / surgical retrieval. Unexplained trauma → safeguarding.
- Rectal mass, or unexplained anal mass or ulcer → consider Suspected cancer referral by site; no FIT wait.
- Rectal bleeding or change in bowel habit → examine; FIT ≥10 µg Hb/g → colorectal Suspected cancer pathway. Negative FIT never delays referral if concern remains.
- Tenesmus + weight loss → Urgent assessment, routed by findings (or FIT per NG12).
- HIV or immunosuppressed → low threshold for proctoscopy + biopsy (CMV, HSV, cancer); GUM / colorectal.
3Assess
☐ Inspect: part the buttocks — fissure, abscess, fistula opening, prolapse ☐ PR with consent and chaperone; no forced DRE in severe fissure; defer if abscess; specialist examination if not possible or inconclusive ☐ Sexual history → rectal NAAT (gonorrhoea, chlamydia incl. LGV), HSV swab, HIV / syphilis by risk ☐ FBC, CRP if infection; HbA1c by diabetes risk or recurrent sepsis; calprotectin if atypical fissure
Not in primary care: draining an abscess or biopsy. Lidocaine must not delay referral or mask a lesion.
4Classify — only if blocks 0–2 are negative
- Typical fissure — posterior midline tear; chronic (≥6 weeks): sentinel pile, indurated edges → block 5.
- Atypical fissure — lateral, multiple, painless, non-healing → Crohn's, HIV, TB, syphilis, cancer → assess further.
- Thrombosed external pile — most settle; severe within about 72 h → urgent surgical assessment for excision may be considered.
- Fistula-in-ano — persistent discharge, recurrent abscess, external opening → colorectal.
- STI proctitis → sexual health; don't delay empirical treatment if convincing (LGV: doxycycline 21 days).
- Proctalgia fugax / levator ani — only once fissure, abscess, proctitis, IBD and cancer are excluded → reassure, warmth.
- Uncertain — say so; specialist examination; safety-net.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Soft stool: gradual fibre, adequate fluid, one laxative by stool consistency; no straining.
- Persistent or chronic fissure: GTN 0.4% per local protocol, usually 6–8 weeks; warn about headache; not with PDE-5 inhibitors or nitrates, or in pregnancy. Alternative: diltiazem 2% (off-label).
- Pain: paracetamol; NSAID only if no bleeding, anticoagulant, renal, heart failure, ulcer, frailty or GI risk; lidocaine, sitz baths, ice.
- Abscess antibiotics: adjunct only — systemic illness, spreading cellulitis, immunosuppression, diabetes, extensive or recurrent disease; never instead of drainage.
6Refer routinely
- Fissure not healing after 6–8 weeks of topical treatment, recurrent or atypical → colorectal.
- Fistula-in-ano, recurrent abscess → colorectal. Haemorrhoids with persistent prolapse, bleeding, pain, irreducibility or failed conservative care → colorectal.
- GUM: STI or HSV proctitis, MSM or HIV-positive with anal symptoms.
7Never reassure by
- Antibiotics alone for a perianal abscess.
- The absence of crepitus or fever when infection is spreading.
- Blaming bleeding on piles or a fissure without examination.
- A negative or unreturned FIT when there is a mass or ongoing concern.
- Labelling proctalgia fugax before excluding serious causes.
- Repeating ointment for an atypical or non-healing fissure.
8Safety-net — say it, then document it
999 “Rapidly spreading redness or swelling around the anus or genitals, severe pain, crackling under the skin, feeling very unwell, or sudden severe tummy pain: call 999.” Same-day “A new painful swelling, a drained wound that won't heal, much worse symptoms, or new bleeding during treatment: contact the GP today.” Review fissure at 6–8 weeks; no cancer appointment → patient phones the hospital.
✓Safe to leave primary care only if — all five, documented
No block 0–2 trigger; sepsis excluded
Inspected; PR or specialist exam arranged
Mass or ulcer excluded or referred; bleeding per NG12
Diabetes, immunosuppression and STI risk considered
Review booked; safety-net given and documented
Summary of the full Reasoning GP anal pain algorithm, which holds history, differentials, treatment detail, prevention and evidence. Sources: NICE NG12 (updated April 2026), NICE HTG690 (quantitative FIT; formerly DG56), BASHH STI guidelines (anogenital herpes 2024, LGV), ESCP cryptoglandular anal fistula guideline 2023, ACPGBI anorectal guidelines; local policy. Clinical reference — follow local pathways.