Elevated CRP 🔥
How to interpret a raised CRP on the ward. Context, magnitude, trend, common causes, targeted workup, and when to escalate for NCHDs.
🔍 Context
- CRP is an acute-phase reactant produced by the liver in response to inflammation; it is sensitive but non-specific.
- Always interpret with the clinical picture: vitals, symptoms, examination, and trend rather than an isolated value.
- Check the local reference range on the lab report (often <5 mg/L in adults, but varies by assay).
- Establish baseline if available (previous admissions, GP letters, pre-op value).
- Recent surgery, trauma, or burns commonly raise CRP for several days, expected unless the patient is deteriorating.
- CRP typically rises within 6–12 hours of an inflammatory stimulus and falls if the process resolves; a falling CRP supports effective treatment.
📊 How to interpret the value
- The bands below are a rough ward guide only, not diagnostic cutoffs; overlap between causes is common.
- Viral infection often causes a smaller CRP rise than bacterial infection, but values overlap and cannot reliably distinguish the two on their own.
- Mild elevation (roughly 5–50 mg/L): often localised infection, inflammation, or post-operative change; correlate clinically.
- Moderate elevation (roughly 50–100 mg/L): more likely significant bacterial infection or active inflammatory disease.
- Marked elevation (>100 mg/L): strongly suggests bacterial infection, abscess, or major tissue injury, but can also occur in severe inflammatory conditions.
- Very high CRP does not equal sepsis on its own; a well patient with localised cellulitis may have CRP >100 mg/L.
- A normal or mildly elevated CRP does not exclude infection, especially early in the illness, on antibiotics, or in immunosuppressed patients.
- Trend matters more than a single value: compare with previous results and expected trajectory (e.g. post-op day 1 vs day 5).
- ESR rises more slowly and stays elevated longer; useful for chronic inflammatory conditions; request if rheumatological or malignancy workup is needed.
⚠️ When to act urgently
- Patient is unwell: tachycardia, hypotension, confusion, rigors, hypoxia, or reduced urine output; complete a sepsis screen regardless of CRP magnitude.
- Rising CRP with clinical deterioration or new organ dysfunction.
- Suspected deep infection: abscess, joint sepsis, line infection, necrotising infection, or post-operative wound concern.
- Immunocompromised or febrile neutropenia; low threshold for septic screen and senior input.
- Use the HSE adult sepsis screening form when infection is confirmed or suspected with relevant triggers.
🧾 History
- Reason for admission and day of illness or post-op day.
- Fever, rigors, sweats, pain, cough, dysuria, diarrhoea, wound or line symptoms.
- Recent surgery, procedures, trauma, or new medications (including biologics, chemotherapy).
- Known inflammatory conditions (RA, IBD, vasculitis) and baseline inflammatory marker pattern.
- Immunosuppression, steroids, or recent antibiotics (may blunt CRP rise).
- Devices: central line, urinary catheter, drain, pacemaker, prosthetic joint.
🩺 Examination
- Full set of vitals and fluid status.
- Systematic search for source: chest, abdomen, skin/soft tissue, joints, line sites, surgical wounds, mouth, perianal area.
- Neurological assessment if confusion or meningism.
- Document findings; CRP alone rarely localises the source.
🧪 Targeted investigations
- Repeat CRP only if it will change management; focus on finding the source.
- FBC (neutrophilia, lymphopenia), U&E, LFTs, lactate if unwell.
- Blood cultures before antibiotics if febrile or bacteraemia suspected.
- Urinalysis and culture; wound swabs only if open wound or atypical infection.
- CXR if respiratory symptoms or hypoxia.
- Imaging directed by examination: USS/CT for abscess, deep infection, or post-operative collections.
- Inflammatory/autoimmune panel (ESR, urate, ANA, RF, anti-CCP) only if infection unlikely and rheumatological cause suspected.
📋 Common causes
Bacterial infection
- Clues
- Fever, focal signs, neutrophilia, lactate if unwell
- First steps
- Source-directed cultures and imaging; start empiric antibiotics per local policy if indicated
Post-operative / tissue injury
- Clues
- Expected rise after surgery or tissue injury; timing and peak vary by procedure (often rises over days 1–3, peaks around days 2–5, then falls over 1–2 weeks if uncomplicated)
- First steps
- Examine wound; compare trend; investigate if not falling or patient deteriorating
Cellulitis / soft-tissue infection
- Clues
- Erythema, warmth, tenderness, lymphangitis
- First steps
- Mark borders; start antibiotics; sepsis screen if systemically unwell
Line / device infection
- Clues
- Erythema at site, rigors with line use, positive cultures
- First steps
- Blood cultures from line and periphery; consider line removal and echocardiography if bacteraemic
Pneumonia / UTI / intra-abdominal sepsis
- Clues
- Respiratory, urinary, or abdominal symptoms and signs
- First steps
- CXR, urinalysis, abdominal imaging as indicated; cultures before antibiotics
Inflammatory / autoimmune disease
- Clues
- Joint swelling, rash, GI symptoms, known diagnosis, multi-system involvement
- First steps
- Senior review; ESR; rheumatology input if new diagnosis or flare suspected
Malignancy / occult inflammation
- Clues
- Weight loss, night sweats, persistent unexplained rise
- First steps
- Senior review; consider CT and specialist referral
Drug reaction (DRESS, etc.)
- Clues
- New drug, rash, eosinophilia, hepatitis
- First steps
- Stop culprit drug; senior review; exclude infection first
| Diagnosis | Clues | First steps |
|---|---|---|
| Bacterial infection | Fever, focal signs, neutrophilia, lactate if unwell | Source-directed cultures and imaging; start empiric antibiotics per local policy if indicated |
| Post-operative / tissue injury | Expected rise after surgery or tissue injury; timing and peak vary by procedure (often rises over days 1–3, peaks around days 2–5, then falls over 1–2 weeks if uncomplicated) | Examine wound; compare trend; investigate if not falling or patient deteriorating |
| Cellulitis / soft-tissue infection | Erythema, warmth, tenderness, lymphangitis | Mark borders; start antibiotics; sepsis screen if systemically unwell |
| Line / device infection | Erythema at site, rigors with line use, positive cultures | Blood cultures from line and periphery; consider line removal and echocardiography if bacteraemic |
| Pneumonia / UTI / intra-abdominal sepsis | Respiratory, urinary, or abdominal symptoms and signs | CXR, urinalysis, abdominal imaging as indicated; cultures before antibiotics |
| Inflammatory / autoimmune disease | Joint swelling, rash, GI symptoms, known diagnosis, multi-system involvement | Senior review; ESR; rheumatology input if new diagnosis or flare suspected |
| Malignancy / occult inflammation | Weight loss, night sweats, persistent unexplained rise | Senior review; consider CT and specialist referral |
| Drug reaction (DRESS, etc.) | New drug, rash, eosinophilia, hepatitis | Stop culprit drug; senior review; exclude infection first |
💊 Initial management
- Treat the patient, not the number; a stable patient with mild CRP and clear cause may need observation only.
- If infection suspected: cultures before antibiotics where possible; start empiric therapy per local policy.
- Remove or replace infected lines/devices when clinically indicated.
- Repeat bloods and review response; expect CRP to fall over days if source is controlled.
- Avoid repeated daily CRP unless it guides a specific decision (e.g. post-op monitoring, treatment response).
- Discuss with senior if cause unclear, CRP rising despite treatment, or patient clinically unwell.
📞 When to refer
- Microbiology / infectious diseases: complex infection, bacteraemia, prosthetic joint infection, endocarditis concern.
- Surgical team: post-operative collection, wound dehiscence, abscess needing drainage.
- Rheumatology: suspected flare or new inflammatory arthritis / vasculitis.
- Haematology / oncology: febrile neutropenia or immunocompromised patient.
- Critical care: sepsis with organ dysfunction or haemodynamic instability.
Based on
Related NICE guidance
NICENICE NG253 — Suspected sepsis in people aged 16 or over: recognition, assessment and early management
Full guidance on nice.org.uk. BetterCall is not endorsed by NICE.
Note Template
Ready-to-use clinical note structure
🕒 08 / 10 / 2026 — 16:07 ATRP re: raised CRP Patient: [age] [sex] Admission Dx: [reason for admission] PMHx: [relevant background, immunosuppression, inflammatory conditions] 🧾 Hx: • CRP: [value] on [date], previous [value / not available] • Symptoms: [fever, pain, cough, dysuria, wound/line symptoms] • Recent surgery, procedures, or antibiotics? • Devices: [line / catheter / drain] 🩺 Exam: • Vitals: HR __ BP __ Temp __ RR __ SpO₂ __ • Source search: chest / abdomen / skin / joints / line sites / wounds 📋 Impression: Likely cause: [infection / post-op / inflammatory / unclear] 📌 Plan: • Targeted cultures and imaging as indicated • Treat source; start empiric antibiotics if clinically indicated • Repeat CRP only if it will change management • Sepsis screen if unwell • Senior review if cause unclear or not improving 👤 [Your Name], [Role] IMC: _______
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