What is the 30-day mortality for each CRB-65 score?

Based on BTS validation studies: CRB-65 score 0 = 30-day mortality approximately 0.7–1.2% (low risk); CRB-65 score 1 = approximately 5–8% (moderate risk); CRB-65 score 2 = approximately 12–15% (moderate-high risk); CRB-65 score 3–4 = approximately 20–30% (high risk). These estimates reflect community-based validation and actual rates may vary by population and comorbidities.

When should a CRB-65 score 1-2 patient be hospitalized vs managed outpatient?

CRB-65 scores 1–2 represent the gray zone where clinical judgment is most critical. Hospitalization generally recommended when: SpO2 <94% on room air, bilateral or multilobar infiltrates, unable to take oral medications, significant comorbidities (COPD, heart failure, immunosuppression), older adult with functional decline, poor social support or no access to follow-up, or clinical appearance worse than score suggests. Close outpatient management with 24-hour telephone review may be appropriate for selected score-1 patients.

How is Legionella pneumonia diagnosed?

Legionella pneumonia (Legionnaires' disease) is typically a severe CAP presenting with high fever, nonproductive cough, hyponatremia, elevated LFTs, and often diarrhea. Urinary Legionella antigen test (sensitivity 70–80%, specificity >99%) is the fastest diagnostic test. Sputum culture on BCYE agar is the definitive test but takes days. All hospitalized CAP patients should receive Legionella urinary antigen per IDSA/ATS guidelines.

What is the difference between CAP and hospital-acquired pneumonia?

CAP develops outside the hospital (within 48 hours of admission in previously well patients). HAP develops 48 or more hours after hospital admission. Key differences: (1) Microbiology — CAP is dominated by Streptococcus pneumoniae; HAP involves gram-negatives (Klebsiella, Pseudomonas, E. coli) and MRSA. (2) Antibiotic selection — HAP requires broader-spectrum coverage. (3) Scoring — CURB-65/CRB-65 apply to CAP only; APACHE II or CPIS to HAP.

What is walking pneumonia and how does it relate to CRB-65?

Walking pneumonia is a colloquial term for mild atypical CAP where the patient is symptomatic but ambulatory. It typically represents Mycoplasma or Chlamydophila infection. These patients often have CRB-65 score 0 and are suitable for outpatient treatment with a macrolide or doxycycline. The term is not a clinical diagnosis — confirm with chest X-ray and treat appropriately based on CRB-65 risk.

Does CRB-65 work in COVID-19 pneumonia?

CRB-65 was not specifically validated for COVID-19. During the pandemic, studies showed variable performance of standard pneumonia scores in COVID-19. COVID-19-specific severity tools (4C Mortality Score, WHO severity criteria) or standard hospital early warning scores (NEWS2) may be more appropriate. That said, CRB-65 can provide a general severity estimate in resource-limited settings or when specific COVID tools are unavailable.

What is the evidence behind CRB-65?

CRB-65 was derived as a simplified version of CURB-65 by Lim et al. (Thorax 2003) from a validation study of 1,068 patients with CAP across 3 UK teaching hospitals. CURB-65 (and by extension CRB-65) is endorsed by BTS Guidelines for Management of CAP (Lim et al., Thorax 2009) and referenced in IDSA/ATS 2019 Community-Acquired Pneumonia Guidelines (Metlay et al., Am J Respir Crit Care Med 2019).

Online Medical Tools — CRB-65 Score

Printed on 9/2/2026

For informational purposes only. This is not medical advice.

Emergency

CRB-65 Score

CRB-65 is a simplified pneumonia risk score derived from CURB-65 that removes the blood urea (BUN) requirement. It uses four bedside variables: Confusion, Respiratory rate, Blood pressure, and age 65 or older. It is especially useful in primary care, urgent care, and prehospital settings where immediate labs are not available.

Formula: CRB-65 = Confusion + Respiratory rate ≥30 + low blood pressure + age ≥65 (0-4 total).

Confusion (new disorientation)

Respiratory Rate ≥ 30/min

Low Blood Pressure (SBP < 90 or DBP ≤ 60 mmHg)

Age ≥ 65 years

Save your results with a free account

Keep a history of calculations, favorite tools, and access your dashboard anytime.

Create free account Sign in

How It Works

Score 4 bedside variables — no labs required

Assess four items that can be evaluated at the bedside without any laboratory testing: Confusion (new disorientation to person, place, or time), Respiratory rate ≥30 breaths per minute, Blood pressure below threshold (systolic <90 mmHg OR diastolic ≤60 mmHg), and Age ≥65 years. Each criterion present scores 1 point.

Sum the total score (0–4)

Add up applicable items. The total CRB-65 score ranges from 0 to 4. Because BUN is excluded (unlike CURB-65), the maximum achievable score is 4, not 5. Calculate the score while evaluating the patient — it takes under 30 seconds to complete.

Apply the risk classification and disposition recommendation

CRB-65 score 0 = low mortality risk (<1%) — outpatient oral antibiotic treatment appropriate; CRB-65 score 1–2 = moderate risk — consider hospitalization or urgent face-to-face evaluation with close follow-up; CRB-65 score 3–4 = high mortality risk — immediate hospital admission required, consider ICU for score 4. Always supplement with SpO2 measurement.

Who Uses the CRB-65 Score

Primary Care and Urgent Care CAP Disposition

Family medicine, urgent care, general practitioners

CRB-65 is specifically designed for settings where BUN is not immediately available. In primary care and urgent care settings, CRB-65 score 0 enables safe same-day discharge with oral antibiotics; scores 1–2 prompt a call to the ED or same-day hospital evaluation; score 3–4 triggers immediate 999/911 or emergency referral.

Emergency Department CAP Severity When BUN Unavailable

Emergency physicians, nurses

In emergency settings where lab results are pending, CRB-65 enables immediate risk stratification while awaiting BUN results. Once BUN returns, CURB-65 provides a more complete picture. CRB-65 is the appropriate initial triage tool in the first minutes after patient presentation.

Triaging Low-Risk Pneumonia for Outpatient Treatment

All clinicians managing CAP

CRB-65 score 0 identifies patients with very low 30-day mortality risk (<1%). These patients can safely receive outpatient oral amoxicillin (with or without a macrolide for atypical coverage) without hospitalization, reducing unnecessary admissions and healthcare-associated complications.

Guiding Antibiotic Choice by Severity

All prescribers

CRB-65 score directly guides antibiotic intensity: Score 0 = oral amoxicillin ± macrolide (outpatient); Score 1–2 = consider IV beta-lactam + macrolide or respiratory fluoroquinolone (ward); Score 3–4 = IV broad-spectrum antibiotics including Legionella and MRSA coverage assessment (high-acuity setting).

Informing Patients About Pneumonia Severity

All clinicians

CRB-65 provides an objective, easy-to-communicate risk estimate. Explaining to patients that a score of 0 means very low risk enables shared decision-making about outpatient treatment, while higher scores provide evidence for recommending hospitalization even to patients who feel 'not that sick.'

Pro Tips

CRB-65 is CURB-65 without BUN — ideal for primary care

The only difference between CRB-65 and CURB-65 is the absence of the BUN (blood urea nitrogen) criterion. CRB-65 maximum score is 4 (vs 5 for CURB-65). When laboratory results are available in hospital settings, CURB-65 is preferred for its additional discriminative power. When lab results are unavailable, CRB-65 provides equivalent guidance.

Always obtain SpO2 in addition to CRB-65

Hypoxia (SpO2 <94% or <90%) is not included in CRB-65 but is a critical independent predictor of pneumonia severity. A patient with CRB-65 of 0 but SpO2 of 88% on room air needs hospital evaluation regardless. Always measure SpO2 before making a disposition decision based on CRB-65.

CRB-65 score 0 = <1% mortality — safe for outpatient oral antibiotics

In the BTS validation studies, CRB-65 score 0 was associated with 30-day mortality below 1%. These patients can be safely treated with oral amoxicillin 500 mg three times daily for 5–7 days (BTS preferred first-line) in non-penicillin-allergic adults. Add a macrolide (azithromycin or clarithromycin) if atypical coverage is needed.

Always consider social factors in pneumonia disposition

Even a CRB-65 score of 0 does not guarantee safe outpatient treatment if the patient cannot take oral medications, lives alone with no support, has significant frailty, or lacks access to follow-up. Social factors, functional status, and ability to recognize deterioration are clinical inputs that can override low-score reassurance.

Bilateral or multilobar pneumonia increases severity beyond CRB-65 score

Bilateral or multilobar pneumonia significantly increases mortality risk independently of CRB-65 or CURB-65 score. If chest X-ray shows bilateral infiltrates or two or more lobe involvement, hospitalization is generally recommended regardless of CRB-65 score, particularly in older or immunocompromised patients.

Legionella and MRSA risk factors should be assessed separately from CRB-65

CRB-65 does not incorporate Legionella risk factors (recent travel, hotel stays, construction exposure, spa/whirlpool exposure) or MRSA risk factors (prior MRSA colonization, recent hospitalization, dialysis, skin and soft tissue infections). Severe CAP with these risk factors warrants urinary antigen testing (Legionella, pneumococcal) and potentially MRSA coverage.

Atypical organisms more common in young healthy patients

Atypical CAP pathogens (Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella spp.) account for 15–25% of CAP. Young, healthy patients with 'walking pneumonia' (productive cough, low-grade fever, bilateral patchy infiltrates, otherwise ambulatory) are more likely to have atypical pathogens — azithromycin or doxycycline provides appropriate coverage in outpatient low-risk CRB-65 score 0 patients.

Hospital-acquired pneumonia requires different scoring tools

CRB-65 and CURB-65 were validated exclusively for community-acquired pneumonia (CAP). Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) have different microbiology (gram-negative rods, MRSA, Pseudomonas) and require different severity tools such as APACHE II or the Clinical Pulmonary Infection Score (CPIS). Never use CRB-65 for HAP/VAP.

Common Questions About Your Results

When laboratory results are available in the emergency department, CURB-65 (which includes BUN) or PSI (Pneumonia Severity Index) provide better discriminative accuracy than CRB-65 alone. PSI has 20 variables and higher sensitivity for low-risk patients. CURB-65 is simpler and equally endorsed by guidelines. CRB-65 is most valuable when labs are unavailable or delayed — it enables triage while awaiting lab results.

Confusion in CRB-65 refers to new-onset disorientation to person, place, or time — not chronic baseline dementia or encephalopathy. Use the Abbreviated Mental Test Score (AMTS ≤8) or direct orientation testing. If the patient has pre-existing cognitive impairment, assess whether there is acute change from their documented baseline. Acute worsening of chronic confusion still scores as positive.

Evidence-Based Methodology

CRB-65 derived from CURB-65 (Lim et al., Thorax 2003) by removing the BUN (urea) criterion for primary care applicability. CURB-65 validated in 1068 patients across 3 UK teaching hospitals; 30-day mortality: score 0=0.7%, 1=3.2%, 2=13%, 3=17%, 4-5=57%. BTS Guidelines for Management of CAP (Lim et al., Thorax 2009) recommend both scores. IDSA/ATS 2019 Community-Acquired Pneumonia Guidelines (Metlay et al., Am J Respir Crit Care Med 2019) reference severity assessment tools for treatment intensity.

Clinical Content Trust

Last reviewed:: April 21, 2026
Guideline version:: General evidence framework v2026.04
Source set version:: Primary-source set v1

How to Interpret Your Result

CRB-65 estimates short-term pneumonia risk using bedside variables only. Score 0 generally indicates lower risk, scores 1-2 indicate intermediate risk, and scores 3-4 indicate high risk with greater likelihood of adverse outcomes.

Use this as a structured triage aid, not as a stand-alone discharge decision.

When to Use This Tool

Use CRB-65 for adults with suspected community-acquired pneumonia when laboratory testing is unavailable or delayed, especially in primary care, urgent care, tele-triage, and prehospital settings.

It helps decide whether outpatient management may be reasonable or whether urgent hospital assessment is warranted.

Limitations

CRB-65 does not include oxygenation, imaging burden, lactate, comorbidity complexity, or biomarker data. Young patients with severe hypoxemia can still have deceptively low scores.

It is a triage support tool and should be interpreted with full clinical context, including respiratory status and social support.

Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.

Sources

Lim WS, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377-382.

Changelog

April 21, 2026 · trust-baseline
Clinical trust metadata enabled for this tool page with structured review/version fields.

Related Tools

Emergency

CURB-65 Score

Calculate CURB-65 for community-acquired pneumonia severity to guide outpatient treatment, hospital admission, or ICU-level evaluation.

Open Emergency

PSI / PORT Score

Calculate PSI (Pneumonia Severity Index) to classify CAP mortality risk (Class I-V) and guide outpatient treatment, observation, or hospital admission.

Open Emergency

NEWS2 Score

Calculate NEWS2 from vital signs and mental status to detect acute clinical deterioration and guide escalation urgency.

Open Emergency

qSOFA Score

Calculate qSOFA bedside sepsis risk score. A score of 2 or more (altered mentation, RR ≥22, SBP ≤100) flags high-risk infection requiring urgent evaluation.

Open

Frequently Asked Questions

CRB-65 is a simplified clinical severity score for community-acquired pneumonia (CAP) that can be calculated without laboratory tests. It scores four bedside variables: Confusion (new disorientation), Respiratory rate ≥30/min, Blood pressure (systolic <90 OR diastolic ≤60 mmHg), and Age ≥65 years. Each criterion scores 1 point (total 0–4). Score 0 = low risk; 1–2 = moderate risk; 3–4 = high risk.

CRB-65 is CURB-65 without the BUN (blood urea nitrogen) criterion. CURB-65 has 5 items (maximum score 5) while CRB-65 has 4 items (maximum score 4). CURB-65 is preferred in hospital settings where labs are immediately available. CRB-65 is preferred in primary care, urgent care, and prehospital settings where BUN is not immediately accessible. Both tools use the same disposition thresholds for scores 0 and 1.

CRB-65 score 0 identifies patients with 30-day mortality below 1% who are suitable for outpatient oral antibiotic treatment. Additional criteria for home treatment: SpO2 ≥94% on room air, no bilateral/multilobar infiltrates, no comorbidities requiring hospital monitoring, able to take oral medications, adequate home support, and access to follow-up within 48 hours if not improving. Oral amoxicillin (with macrolide for atypical coverage) is the BTS recommended first-line therapy.

Community-acquired pneumonia (CAP) is a lower respiratory tract infection acquired outside the hospital or healthcare facility setting. Common bacterial causes include Streptococcus pneumoniae (most common), Haemophilus influenzae, Mycoplasma pneumoniae (atypical), Chlamydophila pneumoniae, Legionella pneumophila (severe atypical). Viral pneumonia (influenza, SARS-CoV-2) can present identically. The causative pathogen influences antibiotic selection.

For low-risk CRB-65 score 0 CAP (outpatient treatment): First-line per BTS guidelines — amoxicillin 500 mg three times daily for 5–7 days. If atypical coverage needed (young patient, bilateral 'walking pneumonia' appearance) — add clarithromycin 500 mg twice daily or use azithromycin 500 mg day 1 then 250 mg daily for 4 days. Penicillin-allergic patients: doxycycline 200 mg loading dose then 100 mg daily, or levofloxacin 750 mg daily.

Online Medical Tools — CRB-65 Score

CRB-65 Score

How It Works

Score 4 bedside variables — no labs required

Sum the total score (0–4)

Apply the risk classification and disposition recommendation

Who Uses the CRB-65 Score

Primary Care and Urgent Care CAP Disposition

Emergency Department CAP Severity When BUN Unavailable

Triaging Low-Risk Pneumonia for Outpatient Treatment

Guiding Antibiotic Choice by Severity

Informing Patients About Pneumonia Severity

Pro Tips

CRB-65 is CURB-65 without BUN — ideal for primary care

Always obtain SpO2 in addition to CRB-65

CRB-65 score 0 = <1% mortality — safe for outpatient oral antibiotics

Always consider social factors in pneumonia disposition

Bilateral or multilobar pneumonia increases severity beyond CRB-65 score

Legionella and MRSA risk factors should be assessed separately from CRB-65

Atypical organisms more common in young healthy patients

Hospital-acquired pneumonia requires different scoring tools

Common Questions About Your Results

Evidence-Based Methodology

Clinical Content Trust

How to Interpret Your Result

When to Use This Tool

Limitations

Sources

Changelog

Related Tools

CURB-65 Score

PSI / PORT Score

NEWS2 Score

qSOFA Score

Further Reading

A Complete Guide to Emergency Medicine: Decision Tools, Scoring Systems, and Clinical Protocols

Frequently Asked Questions