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Category Medicine & Tests

C Confusion New mental confusion (AMT ≤ 8) U Urea > 7 mmol/L Blood urea nitrogen > 19.6 mg/dL R Respiratory Rate ≥ 30/min Tachypnea at presentation B Blood Pressure (low) Systolic < 90 mmHg or Diastolic ≤ 60 mmHg 65 Age ≥ 65 years Patient age 65 or older

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About

The CURB-65 score is a validated clinical prediction rule developed by the British Thoracic Society for estimating 30-day mortality in community-acquired pneumonia (CAP). It assigns 1 point each for five criteria: Confusion (Abbreviated Mental Test score ≤ 8), Urea > 7 mmol/L, Respiratory rate ≥ 30 breaths/min, Blood pressure (systolic < 90 mmHg or diastolic ≤ 60 mmHg), and age ≥ 65 years. Misclassifying a high-risk patient as low-risk delays escalation to intensive care and increases mortality. Conversely, admitting every low-risk patient wastes critical bed capacity. This tool computes the exact score and maps it to the published mortality strata from Lim et al. (2003), where a score of 0 - 1 carried 1.5% 30-day mortality versus 22% at scores 3 - 5.

This calculator approximates risk under the assumption that the clinician has accurately assessed each criterion at the bedside. It does not replace clinical judgment, imaging findings, or co-morbidity assessment. Note: the simplified CRB-65 variant (omitting urea) is used in primary care where laboratory access is limited. Pro Tip: always correlate the score with oxygen saturation and chest radiograph progression before finalizing disposition.

Formulas

The CURB-65 score is computed as a simple additive binary model. Each clinical criterion that is met adds 1 point to the total.

S = C + U + R + B + A

Where each variable is binary (0 or 1):

S - Total CURB-65 score, range [0, 5]

C - Confusion present (AMT ≤ 8): 1 if true, 0 if false

U - Urea > 7 mmol/L: 1 if true, 0 if false

R - Respiratory rate ≥ 30 breaths/min: 1 if true, 0 if false

B - Blood pressure: systolic < 90 mmHg or diastolic ≤ 60 mmHg: 1 if true, 0 if false

A - Age ≥ 65: 1 if true, 0 if false

Risk stratification follows a piecewise mapping:

{

Low risk if S ≤ 1Moderate risk if S = 2High risk if S ≥ 3

Mortality percentages per score level are derived from the original validation cohort (Lim WS, et al. Thorax 2003;58:377-382, n = 1068).

Reference Data

CURB-65 Score	Risk Group	30-Day Mortality	Recommended Disposition	Clinical Action
0	Low	0.6%	Outpatient	Consider home treatment with oral antibiotics
1	Low	2.7%	Outpatient	Home treatment or short-stay observation
2	Moderate	6.8%	Hospital admission	Supervised inpatient care, IV antibiotics
3	High	14.0%	Hospital admission	Urgent admission, consider ICU assessment
4	High	27.8%	ICU consideration	ICU referral, aggressive supportive care
5	High	57.0%	ICU admission	Immediate ICU, vasopressors/ventilation likely
Criterion Thresholds
C - Confusion		AMT score ≤ 8 or new disorientation (person, place, time)
U - Urea		Blood urea nitrogen > 7 mmol/L (> 19.6 mg/dL)
R - Respiratory Rate		≥ 30 breaths/min
B - Blood Pressure		Systolic < 90 mmHg or Diastolic ≤ 60 mmHg
65 - Age		≥ 65 years
Comparison: CURB-65 vs CRB-65 vs PSI
CURB-65		5 criteria, requires lab (urea). Hospital and ED setting.
CRB-65		4 criteria, no lab needed. Primary care / GP setting.
PSI/PORT		20 variables, complex. More sensitive for low-risk identification.
Common CAP Pathogens by Setting
Outpatient (Low)		S. pneumoniae, M. pneumoniae, C. pneumoniae, respiratory viruses
Inpatient (Moderate)		S. pneumoniae, H. influenzae, Legionella spp., mixed flora
ICU (High)		S. pneumoniae, S. aureus, Legionella, Gram-negative bacilli

Frequently Asked Questions

CRB-65 omits the U (urea) criterion, reducing it to 4 variables scored 0 - 4. It was designed for primary care settings where blood tests are not immediately available. The trade-off is reduced discriminatory power: CRB-65 tends to over-triage borderline patients into higher risk groups. If urea results are available, CURB-65 provides better calibration.

No. CURB-65 was derived and validated exclusively on community-acquired pneumonia cohorts. Hospital-acquired pneumonia involves different pathogen spectra (MRSA, Pseudomonas) and baseline patient acuity. For HAP, use clinical pulmonary infection scores (CPIS) or institution-specific sepsis protocols instead.

The AMT is a 10-point bedside cognitive screen. A score ≤ 8 indicates confusion. In practice, many clinicians use the simpler assessment of new disorientation to person, place, or time. The original CURB-65 derivation accepted either method. If formal AMT is impractical, document the basis for your confusion assessment.

PSI uses 20 variables including laboratory values, imaging, and co-morbidities. It is more sensitive for identifying truly low-risk patients (PSI Class I-II) but is cumbersome to compute at the bedside. CURB-65 is preferred when rapid triage is needed (e.g., emergency department). BTS guidelines recommend CURB-65. ATS/IDSA guidelines accept either. Neither score replaces clinical assessment of hypoxemia, multilobar disease, or pleural effusion.

The original criterion uses > 7 mmol/L. The conversion factor is: BUN (mg/dL) = Urea (mmol/L) × 2.8. Therefore the equivalent threshold is BUN > 19.6 mg/dL, typically rounded to > 20 mg/dL in US practice.

No. CURB-65 addresses 30-day mortality risk only. It does not account for hypoxemia (SpO₂ < 92%), bilateral or multilobar infiltrates, significant co-morbidities (e.g., immunosuppression, unstable cardiac disease), inability to take oral medications, or inadequate home support. A score of 0 with any of these factors may still warrant admission. Always pair the score with clinical context.

The age criterion is a binary step function at 65. A 64-year-old and a 20-year-old receive the same 0 for this criterion, despite different baseline risks. This is a known limitation of the scoring system. For patients aged 50 - 64 with significant co-morbidities, consider using PSI which weights age continuously.