CURB-65 — Pneumonia Severity Score
Score 1 point for each criterion present:
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CURB-65 is a widely used clinical severity score for community-acquired pneumonia (CAP) that helps clinicians estimate 30-day mortality risk and determine the appropriate level of care — outpatient management, hospital admission, or intensive care. Developed by the British Thoracic Society (BTS) in 2003 from a large multinational dataset, it is derived from five readily available clinical and laboratory parameters: Confusion (new-onset), elevated Urea (>7 mmol/L or BUN >19 mg/dL), elevated Respiratory Rate (≥30 breaths/min), low Blood Pressure (systolic <90 mmHg OR diastolic ≤60 mmHg), and Age ≥65 years. Each parameter scores one point, giving a total score of 0 to 5. The 30-day mortality associated with each score provides a powerful framework for safe treatment location decisions: score 0–1 suggests low risk (<3% mortality) appropriate for outpatient treatment; score 2 suggests moderate risk (~9% mortality) warranting short-stay hospital admission; scores 3–5 indicate high risk (22–57% mortality) requiring hospitalisation, often with consideration of high-dependency or intensive care admission. A simplified version, CRB-65, omits urea measurement (useful in primary care or resource-limited settings where blood tests are unavailable) and uses only Confusion, Respiratory Rate, Blood Pressure, and Age, with equivalent scoring and interpretation. CURB-65 is validated across international populations and is endorsed by BTS, NICE, the Infectious Diseases Society of America (IDSA), and most major pneumonia guidelines. However, it does not replace clinical judgement — social circumstances, functional status, comorbidities, and patient preference must always be factored into the treatment location decision alongside the score.
CURB-65 Score = C + U + R + B + 65 C = Confusion (new-onset mental confusion): 1 point U = Urea >7 mmol/L (or BUN >19 mg/dL): 1 point R = Respiratory Rate ≥30 breaths/min: 1 point B = Blood Pressure systolic <90 mmHg OR diastolic ≤60 mmHg: 1 point 65 = Age ≥65 years: 1 point Score 0–1: Low risk; consider outpatient treatment Score 2: Moderate risk; consider short-stay or supervised treatment Score 3–5: High risk; hospitalise; consider ICU/HDU at score 4–5
- 1Assess new-onset confusion — score 1 if the patient is disorientated to person, place, or time, or has an acute decline in mental status from baseline.
- 2Check urea from blood biochemistry — score 1 if urea >7 mmol/L (or BUN >19 mg/dL in US units).
- 3Measure respiratory rate — score 1 if ≥30 breaths/min at rest.
- 4Measure blood pressure — score 1 if systolic <90 mmHg OR diastolic ≤60 mmHg.
- 5Determine patient's age — score 1 if aged 65 years or older.
- 6Sum the five components to obtain the CURB-65 score (0–5).
- 7Apply the score to the treatment location recommendation: 0–1 outpatient, 2 hospital assessment/short admission, ≥3 hospital admission (ICU assessment for ≥4).
Score 0 — 30-day mortality <1%; safe for outpatient treatment with oral antibiotics
All parameters are normal. This 52-year-old with CAP has no adverse prognostic features and a predicted 30-day mortality under 1%. Oral amoxicillin (or doxycycline if atypical cover required) as an outpatient is appropriate, with safety-netting advice to return if symptoms worsen or fail to improve in 48–72 hours.
Score 3 — 30-day mortality ~22%; hospital admission indicated; assess for ICU criteria
Three adverse features are present: confusion, elevated urea, and age ≥65. Although respiratory rate and blood pressure are normal, a CURB-65 of 3 indicates significant mortality risk. Hospital admission for IV antibiotics, oxygen, and monitoring is required. PSI (Pneumonia Severity Index) may be used in parallel for a more nuanced assessment.
Score 5 — 30-day mortality approximately 57%; immediate hospital admission; ICU assessment
Maximum CURB-65 score. All five adverse criteria are present, placing this patient in the highest-risk category with a predicted 30-day mortality over 50%. Immediate hospital admission, intravenous broad-spectrum antibiotics, supplemental oxygen, fluid resuscitation, and urgent ICU assessment are required. Blood cultures, ARDS risk stratification, and vasopressor readiness should be planned.
CRB-65 score 1 — low-moderate risk; consider hospital assessment
CRB-65 (without urea) gives a score of 1 purely from the age criterion. In primary care or out-of-hours settings without immediate blood test access, a CRB-65 of 1 suggests the patient could be managed in the community with close follow-up but a hospital assessment may be prudent if there are clinical concerns or social factors.
Emergency department assessment of CAP severity to determine safe discharge versus hospital admission in all adult patients with radiologically confirmed pneumonia.. This application is commonly used by professionals who need precise quantitative analysis to support decision-making, budgeting, and strategic planning in their respective fields
Primary care and out-of-hours CRB-65 assessment (no blood test) to decide whether urgent hospital referral is needed for patients presenting with cough, fever, and pleuritic chest pain.. Industry practitioners rely on this calculation to benchmark performance, compare alternatives, and ensure compliance with established standards and regulatory requirements
Antibiotic stewardship — CURB-65 guides oral versus IV antibiotic selection and anticipated duration of hospital stay for budget planning.. Academic researchers and students use this computation to validate theoretical models, complete coursework assignments, and develop deeper understanding of the underlying mathematical principles
Clinical audit — measuring the proportion of CURB-65 ≥3 patients admitted to general versus high-dependency wards as a quality indicator of pneumonia care.. Financial analysts and planners incorporate this calculation into their workflow to produce accurate forecasts, evaluate risk scenarios, and present data-driven recommendations to stakeholders
Medical education — CURB-65 is taught in virtually every medical school worldwide as the foundational scoring tool for pneumonia management.. This application is commonly used by professionals who need precise quantitative analysis to support decision-making, budgeting, and strategic planning in their respective fields
Immunocompromised Patients
HIV-positive patients, solid organ transplant recipients, haematology patients on immunosuppression, and those on high-dose corticosteroids are at risk of atypical organisms and rapid deterioration from CAP. Even a CURB-65 score of 1–2 may warrant hospital admission in immunocompromised patients. Pneumocystis jirovecii pneumonia (PCP) must be excluded in HIV patients with typical CAP presentation.
Pregnancy
Pregnant women with CAP deteriorate rapidly due to altered respiratory physiology (reduced FRC) and immunological tolerance. Influenza A pneumonia is a leading cause of maternal mortality. CURB-65 parameters (especially respiratory rate) are affected by pregnancy-related physiological changes — the score may underestimate severity. Admission thresholds should be lower in pregnancy, particularly in the third trimester.
COVID-19 Pneumonia
CURB-65 was not designed for COVID-19 and has limited predictive validity for COVID pneumonia severity. Dedicated COVID scoring tools (4C Mortality Score, WHO severity criteria) incorporate oxygen saturation, CRP, and lymphocyte count — parameters specific to COVID-19 pathophysiology. CURB-65 may be used as a guide but should be supplemented with COVID-specific severity assessment.
Aspiration Pneumonia
Aspiration pneumonia (from oropharyngeal or gastric content aspiration) differs from classic community-acquired pneumonia in its bacterial flora (anaerobes, gram-negatives) and treatment requirements. CURB-65 can be applied for severity, but antibiotic choice must cover anaerobes (add metronidazole or use co-amoxiclav/piperacillin-tazobactam) and swallowing assessment is essential before allowing oral intake.
| CURB-65 Score | 30-Day Mortality | Recommendation | Level of Care |
|---|---|---|---|
| 0 | <1% | Outpatient treatment | Community; GP follow-up 48h |
| 1 | ~3% | Consider outpatient with safety-netting | Community or short-stay assessment |
| 2 | ~9% | Hospital admission | General medical ward |
| 3 | ~22% | Hospital admission | Medical ward; consider HDU |
| 4 | ~33% | Hospital admission + ICU assessment | HDU / ICU |
| 5 | ~57% | Hospital admission + ICU | ICU; vasopressors if needed |
What does 'new-onset confusion' mean in the CURB-65 context?
Confusion in CURB-65 is defined as new-onset disorientation to person, place, or time, or an acute deterioration in cognitive function from the patient's established baseline. It does not include pre-existing dementia or long-standing confusion. The abbreviated mental test (AMT) score ≤8/10 is often used to standardise assessment. Delirium secondary to the acute illness is what this criterion is capturing.
Is CURB-65 or PSI (Pneumonia Severity Index) better?
Both are validated. PSI uses 20 variables and provides a more granular risk classification (classes I–V), better identifying low-risk patients for safe outpatient treatment. CURB-65 uses 5 variables and is simpler and faster to calculate at the bedside. CURB-65 is better at identifying high-risk patients needing ICU admission. IDSA/ATS guidelines recommend using either (or both together) alongside clinical judgement.
Can CURB-65 be used for hospital-acquired pneumonia (HAP) or aspiration pneumonia?
CURB-65 was derived and validated specifically for community-acquired pneumonia (CAP). For hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP), different scoring systems and treatment pathways apply (IDSA/ATS HAP guidelines). However, CURB-65 is sometimes used informally outside its validated indication — this should be done cautiously. This is an important consideration when working with curb65 calculations in practical applications. The answer depends on the specific input values and the context in which the calculation is being applied.
What are the limitations of CURB-65?
CURB-65 does not account for comorbidities (immunosuppression, malignancy, liver disease), social factors (living alone, ability to self-care), functional status, or bilateral infiltrates on imaging. Young immunocompromised patients may score low but require admission. Elderly patients with baseline dementia may appear to score for confusion when they are not acutely unwell. Clinical judgement must always supplement the score.
What empirical antibiotic therapy is recommended for CAP by severity?
For low-risk CAP (CURB-65 0–1): oral amoxicillin 500 mg–1 g TDS for 5 days (or doxycycline if atypical cover needed). For moderate-risk CAP (CURB-65 2–3): IV amoxicillin + clarithromycin, or co-amoxiclav + clarithromycin if aspiration suspected. For severe CAP (CURB-65 ≥4): IV co-amoxiclav + clarithromycin, or IV piperacillin-tazobactam in high-risk/healthcare-associated cases, per local antibiogram.
Should I use CURB-65 score or severity to decide ICU admission?
CURB-65 alone should not decide ICU admission — specific major criteria from the IDSA/ATS guidelines (vasopressor requirement, mechanical ventilation need) or minor criteria (RR ≥30, multilobar infiltrates, confusion, BUN ≥20 mg/dL, SBP <90 mmHg, PaO2/FiO2 <250) provide a more nuanced framework. CURB-65 ≥4–5 is a strong signal to trigger ICU assessment.
Is CURB-65 valid in elderly patients?
CURB-65 was developed in a population that included elderly patients and performs reasonably well in this group. However, frailty, functional decline, and dehydration in elderly patients can artificially elevate the score without necessarily predicting the same mortality as in younger patients with the same score. Additionally, elderly patients living alone may need hospital admission even at low CURB-65 scores for social safety reasons.
Does oxygen saturation factor into CURB-65?
No. Oxygen saturation is not one of the five CURB-65 parameters. However, hypoxaemia (SpO2 <92% on room air, or PaO2 <60 mmHg) is an independent marker of severity in CAP and is used in the PSI score and IDSA/ATS criteria. Clinicians should always assess oxygen saturation alongside CURB-65 — a low SpO2 even in a CURB-65 score 1–2 patient may warrant hospital admission.
Pro Tip
Always pair CURB-65 with an assessment of oxygenation (SpO2 on room air) and a chest X-ray. A patient scoring CURB-65 = 1 with SpO2 88% on room air and bilateral infiltrates has a clinical severity that exceeds what the score suggests — these patients typically require hospital admission regardless of the low score.
Did you know?
The CURB-65 score originated from a multinational study by the British Thoracic Society analysing data from over 1,000 patients in three countries (UK, New Zealand, Netherlands). Its genius lies in its extreme simplicity — three clinical observations and two results from a routine blood test — yet it outperforms many complex multivariable models at predicting 30-day mortality, demonstrating that in medicine, simplicity and predictive power are not mutually exclusive.
References
- ›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.
- ›British Thoracic Society. BTS guidelines for the management of community acquired pneumonia in adults. Thorax. 2009;64(Suppl 3):iii1-55.
- ›Mandell LA et al. IDSA/ATS Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults. Clin Infect Dis. 2007;44(Suppl 2):S27-72.
- ›NICE. Pneumonia (community-acquired): antimicrobial prescribing (NG138). 2019.
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