← Full fever in adults algorithm
Reasoning GP · Diagnostic Compass · decision tree

Fever in adults1 PAGE

A feverish adult: is it dangerous, how urgent, and where is the source?
NICE NG253 · NG240 · NG12 (Apr 2026) · NG33
RCP NEWS2 · UKHSA imported fever
Reviewed Oct 2026 · next review Apr 2027
Applies to: adults with a measured fever, face to face or remote. Not children (NG143). Judge severity from physiology and risk group, not the thermometer.
Fever presents

NG253 high risk: SBP ≤90 (or >40 below baseline), HR >130, RR ≥25, ≥40% O₂ to keep SpO₂ >92%, no urine 18 h, mottled; shock · Altered mental state · non-blanching rash · meningism, encephalitis · Neutropenic sepsis · severe malaria · necrotising fasciitis · epiglottitis · Back pain + deficit → emergency + MRI · hyperthermia → emergency admission

Emergency?
YES
CALL 999
Never delay transfer for bloods, cultures, urine or antibiotics. Meningococcal: benzylpenicillin 1.2 g IV/IM (or ceftriaxone) unless it delays transfer. Neutropenic: no FBC wait, no oral antibiotic. Hyperthermia: cool.
NO

Asplenia, sickle cell → same-day admission · immunosuppressed: escalate early · device, line, surgery · Malaria-area travel → malaria test same day; VHF risk: isolate, UKHSA first · Endocarditis · hot joint or prosthesis → same-day ortho · GCA: prednisolone now, refer urgently; same day if visual symptoms · Unwell or frail, no source → same day · Unexplained fever → consider very urgent FBC within 48 h; nodes or spleen → lymphoma pathway

Same day or urgent?
YES
SAME DAY · 48 H FBC
Endocarditis: cultures first if stable; joint: aspirate before antibiotics. GCA: prednisolone 40–60 mg now; visual symptoms: 60 mg if IV methylprednisolone is not immediate; no wait for ESR or biopsy. Cough >3 weeks, sweats, weight loss: CXR, TB.
NO
Which pattern?
Viral, <5 dayswell, normal obs
  1. No routine tests, no antibiotic; usually 3–5 days.
  2. Paracetamol for comfort; fluids; no tepid sponging.
  3. No source, frail or antibiotic → review 48 h.
Bacterial sourcestable, source found
  1. Treat the source (CAP, lower UTI, cellulitis, strep throat).
  2. Cultures first where feasible; shortest course.
  3. Review at 48–72 h; de-escalate or stop.
5–14 daysnot simple viral
  1. Re-examine undressed; full sweep.
  2. Targeted bloods; CXR if respiratory or unexplained.
  3. Unwell or frail, no source → same day.
>3 weeksno diagnosis
  1. Re-take history; re-examine.
  2. Endocarditis, TB, lymphoma, abscess, inflammatory.
  3. Refer general medicine or ID; no empirical antibiotics.
EVERY PATIENT

Tests that change management

  • Unwell: SpO₂, glucose, urine if urinary symptoms, pregnancy test; FBC, U&E, LFTs, CRP; blood cultures if sepsis, rigors, endocarditis.
  • Very urgent FBC within 48 h (NG12); CXR; USS for a collection.
  • Travel: same-day malaria film/RDT; repeat if suspicion remains.
  • PUO: largely secondary care. Not for every fever: LDH, broad serology.

Safety-net · follow up

  • 999: rash that does not fade, confusion, stiff neck, breathless, mottled, a fit, no urine 18 h.
  • Today: much worse, fever >5 days, no fluids; neutropenic, asplenic or after travel.
  • Review 48 h if no source, frail or on antibiotic; chase cultures; written safety-net.
Never: Reassure by a fever that "breaks", no fever, normal CRP or a low NEWS2 · Treat a dipstick in an older or catheterised patient as the source; call fever with back pain MSK · Delay transfer for tests or antibiotics
Reasoning GP · Fever in adults · decision tree · v1.0 · Oct 2026 · Full algorithm: gpreasoning.uk/tools/algorithms/fever-adults.htmlDecision support, not a substitute for clinical judgement. Check doses in the SPC and your local formulary.