CURB-65 Score Calculator
Estimates 30-day mortality in community-acquired pneumonia and guides disposition decisions — outpatient treatment, hospital admission, or intensive care. Includes the CRB-65 variant for primary care settings where blood urea is unavailable.
Calculate CURB-65 Score
Score each criterion as present or absent. All five criteria are required for the full CURB-65 score. If blood urea is unavailable (e.g., in primary care or pre-hospital settings), use the CRB-65 calculator below.
The CURB-65 score is a severity assessment tool for community-acquired pneumonia (CAP) — it has not been validated for hospital-acquired, ventilator-associated, or aspiration pneumonia. It estimates 30-day mortality risk and guides disposition, but clinical judgement must always be applied. Patients with social vulnerability, inability to take oral medications, unstable comorbidities, or hypoxaemia may require admission regardless of a low CURB-65 score.
CRB-65 Score (No Blood Tests Required)
The CRB-65 omits the urea criterion, making it suitable for primary care and pre-hospital settings where blood tests are not immediately available. It uses the same four remaining criteria (Confusion, Respiratory rate, Blood pressure, age ≥ 65) with a total range of 0–4.
Understanding the CURB-65 Score
The CURB-65 score was developed in 2003 by Lim and colleagues from the British Thoracic Society, derived from a prospective study of over 1,000 patients with community-acquired pneumonia across the UK, New Zealand, and the Netherlands. It was designed to provide a simple, bedside-applicable tool for assessing pneumonia severity and guiding the admission decision — one of the most common and consequential clinical judgements in emergency medicine.
The five criteria were selected from a multivariate analysis of prognostic factors for 30-day mortality. Each criterion carries equal weight (1 point), reflecting independent associations with death from CAP. The mnemonic “CURB-65” makes the score easily memorable and applicable at the bedside without electronic tools.
CURB-65 Criteria
C — Confusion (new onset)
U — Urea > 7 mmol/L
R — Respiratory rate ≥ 30/min
B — Blood pressure (SBP < 90 or DBP ≤ 60)
65 — Age ≥ 65 years
1 point for each criterion present.
Total range: 0–5
Worked Example
A 72-year-old man presents with cough, fever, and dyspnoea. He is confused. RR 34/min, BP 108/62, urea 9.2 mmol/L.
C — Confused: 1 pt
U — Urea 9.2 (> 7): 1 pt
R — RR 34 (≥ 30): 1 pt
B — DBP 62 (> 60): 0 pt
65 — Age 72 (≥ 65): 1 pt
Total: 4 (Severe)
30-day mortality ≈ 27%
Disposition: ICU or high-dependency
CURB-65 vs PSI (Pneumonia Severity Index): The PSI (PORT score) uses 20 variables including comorbidities and laboratory values, providing excellent risk stratification but requiring complex calculation. CURB-65 uses only 5 variables and is faster at the bedside. The two scores perform comparably for predicting mortality, but CURB-65 tends to identify more patients as low-risk suitable for outpatient management, while PSI tends to be more conservative. Both have been endorsed by major guidelines (BTS, ATS/IDSA, ERS).
Score Interpretation & Disposition Guidance
The CURB-65 score stratifies patients into three management groups based on estimated 30-day mortality. Disposition recommendations should be interpreted alongside clinical judgement — social circumstances, functional status, comorbidities, and oxygenation status may modify the disposition decision.
| CURB-65 | Risk Group | 30-Day Mortality | Recommended Disposition |
|---|---|---|---|
| 0 | Low | 0.6% | Outpatient treatment likely appropriate |
| 1 | Low | 2.7% | Outpatient treatment or short observation |
| 2 | Moderate | 6.8% | Consider short inpatient or hospital-supervised outpatient |
| 3 | High | 14.0% | Hospital admission — manage as severe pneumonia |
| 4 | High | 27.8% | Hospital admission — consider ICU or high-dependency |
| 5 | High | 27.8% | Hospital admission — consider ICU or high-dependency |
CRB-65 Interpretation (Primary Care)
| CRB-65 | Risk | Mortality | Action |
|---|---|---|---|
| 0 | Low | ~1.2% | Home treatment may be appropriate |
| 1–2 | Moderate | ~8.2% | Consider hospital referral and assessment |
| 3–4 | High | ~31.3% | Urgent hospital admission |
CURB-65 = 2 is the “admission decision” score. This is the most clinically challenging group — the 6.8% 30-day mortality is significant but not prohibitive. British Thoracic Society guidelines recommend considering hospital-supervised outpatient management or short admission (< 24 hours) for these patients. Key factors that may tip the decision toward admission include hypoxaemia (SpO₂ < 92%), bilateral or multilobar infiltrates, pleural effusion, inability to take oral medication, unstable comorbidities, or inadequate social support.
Clinical Management & Antibiotic Guidance
The CURB-65 score informs not only disposition but also the intensity and route of antibiotic therapy. Empirical antibiotic selection should follow local guidelines and susceptibility patterns, but the severity stratification provides a framework for the general approach.
Patients with CURB-65 0–1 can typically be managed in the community with oral antibiotics, provided they can take oral medication, have adequate social support, and do not have significant hypoxaemia or comorbidity concerns. The 30-day mortality for this group is under 3%, and the vast majority will recover without complications.
First-line antibiotics (per BTS/NICE guidelines): Amoxicillin 500 mg three times daily for 5 days. If penicillin-allergic: doxycycline 200 mg on day 1, then 100 mg daily, or clarithromycin 500 mg twice daily. For patients with moderate CAP or those not responding to first-line: consider amoxicillin plus a macrolide (e.g., clarithromycin) or a respiratory fluoroquinolone (levofloxacin, moxifloxacin) if both beta-lactam and macrolide are unsuitable.
- Duration: 5 days is typically sufficient for uncomplicated CAP; extend to 7–10 days if slow response
- Safety-netting: Advise the patient to return if no improvement within 48 hours, or immediately if worsening breathlessness, inability to keep fluids down, or new confusion
- Follow-up: Chest radiograph at 6 weeks for patients over 50 to exclude underlying malignancy
- Consider admission despite low score if: SpO₂ < 92%, unable to eat/drink, lives alone with no support, unstable comorbidity
CURB-65 2 represents a pivotal decision point. These patients have significant mortality risk (~7%) but may be manageable with hospital-supervised outpatient treatment in some healthcare systems. Many will benefit from a period of observation, intravenous fluid resuscitation, supplemental oxygen assessment, and potentially IV antibiotics before determining whether inpatient care is needed.
Antibiotic approach: Oral amoxicillin 500 mg–1 g TDS plus a macrolide (clarithromycin 500 mg BD), or IV amoxicillin plus clarithromycin if oral intake is unreliable. In penicillin allergy: respiratory fluoroquinolone (levofloxacin 500 mg daily). Reassess within 24–48 hours — if improving on oral therapy with adequate oxygenation, transition to outpatient management with close follow-up.
- Key decision factors favouring admission: SpO₂ < 92%, multilobar infiltrates, significant pleural effusion, comorbid heart failure or COPD, rising urea, or social isolation
- Key factors supporting discharge: SpO₂ ≥ 94% on air, single lobar consolidation, oral intake maintained, reliable follow-up available
- Hospital-at-home: Where available, early supported discharge or hospital-at-home services can safely manage selected CURB-65 2 patients outside the hospital
Patients with CURB-65 ≥ 3 have a 30-day mortality of 14–28% and require hospital admission with intravenous antibiotics and close monitoring. Those scoring 4–5 should be assessed for ICU or high-dependency unit admission, particularly if there is evidence of sepsis, multi-organ dysfunction, or respiratory failure requiring ventilatory support.
Antibiotic approach: IV co-amoxiclav (or IV ceftriaxone/cefuroxime) plus IV clarithromycin (or oral if tolerated). Alternatives in severe penicillin allergy: IV levofloxacin 500 mg daily. Duration: 7–10 days for severe CAP, extended if complications arise (empyema, lung abscess, bacteraemia). Consider Legionella urinary antigen and pneumococcal antigen testing. Blood cultures before antibiotics. If risk factors for Pseudomonas (structural lung disease, recent antibiotics, recent hospitalisation), broaden cover to piperacillin-tazobactam or meropenem.
- ICU referral criteria (BTS): Mechanical ventilation required, or ≥ 2 of: confusion, urea > 7, RR ≥ 30, SBP < 90, bilateral/multilobar, PaO₂/FiO₂ < 250
- Adjunctive measures: Supplemental oxygen (target SpO₂ 94–98%, or 88–92% in COPD), IV fluids, VTE prophylaxis, early mobilisation when stable
- Corticosteroids: Dexamethasone 6 mg daily for 4 days may reduce mortality in hospitalised CAP — supported by the CAPE-COD and other recent trials
- Treatment failure: If no improvement by 48–72 hours, reassess: consider atypical organisms, resistant pathogens, empyema, or alternative diagnosis
Streptococcus pneumoniae remains the most commonly identified pathogen in CAP across all severity levels, accounting for approximately 30–40% of cases where a microbiological diagnosis is achieved. It is the classic cause of lobar pneumonia with abrupt onset, rigors, pleuritic chest pain, and rust-coloured sputum. Other frequent bacterial causes include Haemophilus influenzae (particularly in COPD patients), Moraxella catarrhalis, and Staphylococcus aureus (post-influenza, injection drug users).
Atypical organisms — Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila — account for approximately 10–20% of CAP and are important considerations in moderate-to-severe disease. Legionella in particular is associated with severe CAP, hyponatraemia, diarrhoea, and elevated liver enzymes. Viral causes (influenza, SARS-CoV-2, RSV, parainfluenza) account for an increasing proportion of identified CAP, particularly during winter respiratory seasons.
- Typical organisms: S. pneumoniae, H. influenzae, M. catarrhalis, S. aureus, Klebsiella (alcoholism)
- Atypical organisms: Mycoplasma, Chlamydophila, Legionella, Coxiella burnetii (Q fever)
- Viral: Influenza A/B, SARS-CoV-2, RSV, adenovirus, human metapneumovirus
- In ~50% of CAP cases: No pathogen is identified despite appropriate investigation
Parapneumonic effusion and empyema are the most important local complications. Approximately 40% of hospitalised CAP patients develop a parapneumonic effusion; of these, about 10–15% progress to empyema requiring chest tube drainage or surgical intervention. Clinical clues include persistent fever despite appropriate antibiotics, pleuritic pain, and a laterally displaced trachea. Diagnostic thoracentesis is indicated if the effusion is ≥ 10 mm on lateral decubitus film or occupies > 50% of the hemithorax.
Lung abscess may complicate CAP, particularly with aspiration, anaerobic organisms, or S. aureus. Sepsis and multi-organ dysfunction are the most serious systemic complications — CURB-65 ≥ 3 patients should be screened for sepsis criteria (qSOFA, NEWS2) and managed accordingly with early goal-directed therapy. Long-term, CAP is associated with increased cardiovascular risk for up to 10 years following the acute episode — cardiac events occur in approximately 10–30% of hospitalised CAP patients within 30 days.
Antibiotics within 4 hours. For all patients with confirmed or suspected CAP, initiate empirical antibiotic therapy as soon as possible — ideally within 4 hours of presentation. Delays beyond this window are associated with increased mortality. For patients with sepsis criteria, antibiotics should be given within 1 hour. Blood cultures should be drawn before antibiotics in hospitalised patients but must not delay treatment.
Special Populations & Considerations
The CURB-65 score was derived primarily in general adult populations and has known limitations in several important clinical groups. These populations may require modified scoring, additional risk assessment, or adjusted management pathways.
Oxygenation is not in the CURB-65 score. A patient with CURB-65 0 but SpO₂ of 88% on room air requires supplemental oxygen and likely hospital admission — hypoxaemia independently predicts mortality in CAP and is one of the most important parameters not captured by the score. Always measure SpO₂ alongside CURB-65 and use it as an independent modifier of the disposition decision.
Common Pitfalls & Limitations
The CURB-65 is designed for simplicity at the bedside, which inherently limits its granularity. Understanding these pitfalls ensures the score is applied as a guide rather than a rigid protocol.
The CURB-65 does not include oxygenation status, despite SpO₂ and PaO₂/FiO₂ ratio being among the strongest predictors of mortality in CAP. A patient with CURB-65 of 0 who is hypoxaemic (SpO₂ < 92%) on room air is at substantially higher risk than the score implies. Conversely, a patient with CURB-65 3 who is well-oxygenated on room air may be less critically ill than the score suggests.
Clinical impact: Always measure SpO₂ as part of the CURB-65 assessment. If SpO₂ is < 92% on room air (or < 88% in known COPD with chronic hypoxia), consider upgrading the disposition decision by at least one category — e.g., treat a CURB-65 of 1 with hypoxaemia as if it were a 2–3. Arterial blood gas analysis is recommended for all patients requiring supplemental oxygen to assess PaCO₂ and identify type 2 respiratory failure.
The CURB-65 was derived and validated exclusively in community-acquired pneumonia. It has not been validated for hospital-acquired pneumonia (HAP), ventilator-associated pneumonia (VAP), aspiration pneumonia, or pneumonia in immunocompromised hosts. These populations have different aetiologies, risk factors, and mortality profiles that the CURB-65 criteria do not capture.
Clinical impact: Do not use CURB-65 for pneumonia developing ≥ 48 hours after hospital admission (HAP), in ventilated patients (VAP), or in patients with witnessed aspiration events. For HAP and VAP, use institutional guidelines and consider local resistance patterns. For aspiration pneumonia, antibiotic selection differs (anaerobic cover may be needed) and the clinical trajectory is influenced by the volume and content of the aspirate rather than the CURB-65 variables.
Beyond age, the CURB-65 includes no comorbidity data. Patients with significant heart failure, liver disease, renal impairment, malignancy, or neuromuscular disease have higher mortality at every CURB-65 level compared to otherwise healthy individuals. Similarly, functional status (frailty, performance status) is a powerful predictor of outcome that the score ignores.
Clinical impact: A CURB-65 of 1 in a frail 80-year-old with severe COPD and heart failure carries vastly different implications from a CURB-65 of 1 in an otherwise fit 70-year-old. When in doubt about the admission decision, the PSI (PORT score) may be more informative as it incorporates comorbidities, laboratory values, and imaging findings. At minimum, document comorbidities and functional status alongside the CURB-65 score and allow these to modulate the disposition decision.
The “C” in CURB-65 refers specifically to new mental confusion — defined as an Abbreviated Mental Test Score (AMTS) ≤ 8, or new disorientation in person, place, or time. The key word is “new.” Patients with pre-existing dementia or chronic cognitive impairment may have a low AMTS at baseline. Scoring confusion as present in these patients without comparing to their baseline inflates the CURB-65 and may lead to unnecessary hospitalisation.
Clinical impact: Establish the patient’s baseline cognitive function from carers, nursing home records, or prior medical notes. A patient with known moderate dementia and AMTS of 6 at baseline who scores AMTS 5 with pneumonia has not meaningfully deteriorated — this should not count as “confusion” for CURB-65 purposes. Conversely, a patient with normal baseline cognition who is newly disoriented should score the full point even if their AMTS is 9 (just above the formal threshold) because any new confusion in an acute illness is clinically significant.
A CURB-65 of 0–1 suggests suitability for outpatient treatment from a mortality risk perspective, but mortality is not the only reason to admit a patient. Other valid indications for admission include: inability to maintain oral intake (vomiting, severe dysphagia), need for supplemental oxygen, unstable comorbidities triggered by the acute infection (e.g., acute heart failure, COPD exacerbation), social isolation without support at home, inability to fill prescriptions or attend follow-up, suspected empyema or lung abscess on imaging, and concern about adherence to treatment.
Clinical impact: Use the CURB-65 to estimate mortality risk, but make the disposition decision based on the full clinical picture. A useful framework is: “Would I be comfortable with this patient managing at home for the next 48 hours?” If the answer is no — regardless of the CURB-65 score — admission or extended observation is appropriate.
The CURB-65 score does not include imaging findings, oxygen saturation, inflammatory markers (CRP, procalcitonin), lactate, albumin, or comorbidities — all of which independently predict mortality in CAP. It estimates the probability of death, but the disposition decision requires broader clinical assessment. Use CURB-65 as the starting point for the admission conversation, not the final answer.
Quick Reference Summary
| Letter | Criterion | Threshold | Points |
|---|---|---|---|
| C | Confusion | New onset (AMTS ≤ 8) | 1 |
| U | Urea | > 7 mmol/L (BUN > 19 mg/dL) | 1 |
| R | Respiratory rate | ≥ 30 breaths/min | 1 |
| B | Blood pressure | SBP < 90 and/or DBP ≤ 60 | 1 |
| 65 | Age | ≥ 65 years | 1 |
The Golden Rule: CURB-65 estimates the risk of death from pneumonia — not the need for admission. Admission decisions require integrating the score with oxygenation status, imaging findings, comorbidities, functional capacity, and social circumstances. A low CURB-65 is a necessary but not sufficient condition for safe outpatient management.
Disclaimer & References
For Educational Purposes Only. This calculator and the accompanying clinical information are intended as educational tools for healthcare professionals. They do not replace clinical judgement. Results should be interpreted in the full clinical context. Lab reference ranges vary by institution — verify with your own laboratory. Drug dosages should be confirmed against current prescribing information.
References
- Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377-382. DOI: 10.1136/thorax.58.5.377
- Lim WS, Baudouin SV, George RC, et al. BTS guidelines for the management of community acquired pneumonia in adults: update 2009. Thorax. 2009;64(Suppl III):iii1-iii55. DOI: 10.1136/thx.2009.121434
- Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336(4):243-250. DOI: 10.1056/NEJM199701233360402
- Chalmers JD, Singanayagam A, Akram AR, et al. Severity assessment tools for predicting mortality in hospitalised patients with community-acquired pneumonia: systematic review and meta-analysis. Thorax. 2010;65(10):878-883. DOI: 10.1136/thx.2009.133280
- Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia: an official clinical practice guideline of the ATS and IDSA. Am J Respir Crit Care Med. 2019;200(7):e45-e67. DOI: 10.1164/rccm.201908-1581ST
- National Institute for Health and Care Excellence (NICE). Pneumonia in adults: diagnosis and management. Clinical guideline [CG191]. Updated 2019. Available at: nice.org.uk/guidance/cg191
- Dequin PF, Meziani F, Quenot JP, et al. Hydrocortisone in severe community-acquired pneumonia (CAPE COD). N Engl J Med. 2023;388(21):1931-1941. DOI: 10.1056/NEJMoa2215145
- McNally M, Curtain J, O’Brien KK, Dimitrov BD, Fahey T. Validity of British Thoracic Society guidance (the CRB-65 rule) for predicting the severity of pneumonia in general practice. Br J Gen Pract. 2010;60(579):e423-e430. DOI: 10.3399/bjgp10X532422
- Corrales-Medina VF, Musher DM, Wells GA, Chirinos JA, Chen L, Fine MJ. Cardiac complications in patients with community-acquired pneumonia. Circulation. 2012;125(6):773-781. DOI: 10.1161/CIRCULATIONAHA.111.040766
- Torres A, Cilloniz C, Niederman MS, et al. Pneumonia. Nat Rev Dis Primers. 2021;7(1):25. DOI: 10.1038/s41572-021-00259-0