The CURB-65 Calculator or Clinical Tool
The CURB-65 Score in the Assessment and Management of Community-Acquired Pneumonia
In the assessment and management of community-acquired pneumonia (CAP), accurately determining disease severity is of paramount importance. This determination guides critical therapeutic decisions, including whether to admit patients to the hospital or an intensive care unit (ICU), the optimal time for discharge, the necessary extent of diagnostic investigations, and the selection and route of antimicrobial therapy.
Existing Severity Scores and Their Limitations
Pneumonia Severity Index (PSI)
The Pneumonia Severity Index (PSI) developed by Fine and colleagues in the USA has become a prominent tool for stratifying pneumonia patients according to mortality risk and has been featured in North American guidelines. However, its applicability in busy clinical settings is somewhat constrained because it requires calculation based on 20 different variables. Although the PSI effectively identifies patients who can be managed at home (i.e., those at low risk), it is less convenient for rapidly detecting those with severe CAP who require aggressive inpatient or ICU-level care.
Modified British Thoracic Society (mBTS) Criteria
An alternative severity assessment tool proposed by the British Thoracic Society (BTS)—later modified by Neill et al.—focuses on four easily measurable clinical features: mental confusion, respiratory rate (>30 breaths/min), diastolic blood pressure (<60 mmHg), and blood urea (>7 mmol/L). The presence of two or more of these features predicts high mortality risk with approximately 80% sensitivity and specificity. Nonetheless, this tool divides patients only into “severe” or “non-severe” groups, thereby overlooking those with low mortality risk who might be managed safely as outpatients or with early hospital discharge.
Development of the CURB-65 Score
Rationale and Cohort Characteristics
To overcome these limitations, a large prospective study was conducted across three countries with similar primary and secondary healthcare systems (UK, New Zealand, and the Netherlands). Patients were admitted as unselected emergencies to public hospitals, ensuring a representative sample of adults with CAP. Systematic collection of relevant clinical data highlighted the prognostic importance of four “core” adverse features: confusion, hypotension, tachypnea, and raised blood urea. Additionally, advanced age was consistently found to be strongly associated with worse outcomes in CAP.
Core Adverse Features
- Confusion
- Blood Urea >7 mmol/L
- Respiratory Rate >30 breaths/min
- Low Blood Pressure (systolic <90 mmHg or diastolic ≤60 mmHg)
- Age ≥65 years
From these parameters, the CURB score (later adapted to CURB-65 by including age ≥65) was derived to provide a straightforward severity assessment. CURB-65 incorporates only five variables (compared to 20 in the PSI) and relies primarily on clinical observations readily available in most admissions units. Serum urea is often obtainable—even out of hours—and the remaining factors (confusion, respiratory rate, blood pressure, and age) do not require laboratory-intensive investigations.
Stratifying Patients with CURB-65
The resulting CURB-65 score (ranging from 0 to 5) facilitates assigning patients to three mortality risk categories, each associated with distinct clinical management pathways:
- Low Risk (Score 0–1)
- Mortality risk is typically under 2%.
- Such patients may be considered for outpatient management (e.g., by their general practitioner) or for brief observation in the hospital if any social factors or comorbidities merit it.
- Intermediate Risk (Score 2)
- Mortality risk is around 9%.
- Patients often require in-hospital treatment, with intravenous antibiotics and closer clinical surveillance.
- High Risk (Score ≥3)
- Mortality risk exceeds 19%.
- These patients usually meet criteria for severe CAP. Admission to hospital is recommended, and in many cases, ICU or high-dependency care is warranted for close monitoring and management.
This tiered system parallels the risk classifications of the PSI (risk classes I–III vs. IV vs. V) but has the advantage of being simpler, as it relies on fewer, more accessible clinical variables. Consequently, it is more practical in hectic emergency departments or admission units that may have time or resource constraints.
Reference
Lim WS, van der Eerden MM, Laing R, Boersma WG, Karalus N, Town GI, Lewis SA, Macfarlane JT. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003 May;58(5):377-82. doi: 10.1136/thorax.58.5.377. PMID: 12728155; PMCID: PMC1746657.
