CURB-65 Score
Calculate the five-item CURB-65 score for adults with clinically diagnosed community-acquired pneumonia using confusion, urea or BUN, respiratory rate, blood pressure and age.
Content updated: View sources
QuickMedCalc is developed and maintained by an independent developer. Medical content is not independently reviewed by a physician.
Formula and medical content are based on the references listed on this page. See sources, About, and Sources and Review Process.
CURB-65 score
—
A population risk-stratification reference; not a diagnosis or treatment instruction.
NICE hospital mortality-risk group
—
Population band, not an individual prediction or automatic action.
About
CURB-65 is a five-item short-term mortality-risk stratification reference for adults with a clinical diagnosis of community-acquired pneumonia at an initial acute-care assessment. The original model was derived from hospital presentation data; current NICE NG250 uses CURB-65 as an adult hospital CAP risk assessment alongside clinical judgment. It is not a pneumonia diagnosis, a pathogen test, or an individual mortality probability. [1, 2]
This page calculates only values that the user submits: confusion, urea or BUN, respiratory rate, blood pressure, and completed age. It cannot verify the diagnosis, examination, oxygenation, radiograph, comorbidity, or treatment response, and it does not select antibiotics, discharge, admission, ICU care, or another intervention. PSI is a separate model, and ATS/IDSA severe CAP criteria are a different severity framework. [3, 4, 5, 6]
Formula
Interpretation
| CURB-65 score | NICE hospital group | Current NICE population band | Required boundary |
|---|---|---|---|
| 0–1 | Low | less than 3% 30-day mortality risk | not proof that outpatient care is appropriate |
| 2 | Intermediate | 3% to 15% | not an automatic admission rule |
| 3–5 | High | more than 15% | not an automatic ICU or treatment rule |
These are current NICE population risk bands for hospital adults with CAP, not precise probabilities for an individual. The page does not dynamically output location, treatment, escalation, or a mortality prediction. NICE places CURB-65 in clinical context; ATS/IDSA recommends PSI with clinical judgment for hospitalization decisions, while severe CAP criteria answer a different question. [2, 3]
CURB-65 criteria, boundaries, and clinical context
Five CURB-65 criteria
Each criterion contributes one point only. New confusion means an abbreviated Mental Test Score of 8 or less or new disorientation in person, place, or time; stable chronic cognitive impairment without a new change does not automatically score. The BP item is one OR condition, so even when both pressure thresholds are met it contributes only one point. [1, 2]
| Criterion | One-point threshold | Submitted input used | Important boundary or limitation |
|---|---|---|---|
| Confusion | AMTS ≤8 or new disorientation | Yes / No | A stable previous impairment is not automatically new confusion. |
| Urea | >7 mmol/L | Urea mmol/L or BUN mg/dL | Strictly greater than 7; exactly 7 scores 0. |
| Respiratory rate | ≥30 breaths/min | Breaths/min | 29.9 scores 0; 30 scores 1. |
| Blood pressure | SBP <90 or DBP ≤60 mmHg | SBP and DBP in mmHg | One OR item, one point maximum; SBP 90 is not low. |
| Age | ≥65 completed years | Completed years | Age 64 scores 0; age 65 scores 1. |
Urea and BUN handling
The original criterion is urea in mmol/L, and the strict >7 threshold comes from the model and current NICE context. [1, 2] This page accepts BUN in mg/dL and applies BUN ÷ 2.80112 without rounding the normalized value before comparison. A public laboratory conversion table expresses the relationship as 0.357 mmol/L per mg/dL BUN; the implementation uses 1 ÷ 0.357 ≈ 2.80112 as a fixed software convention to preserve the audited boundary and unrounded flow. It does not claim extra measurement precision, and displayed digits do not increase the effective precision of the laboratory result. [7] A unit label must match the entered value; renal function, dehydration, and other non-pneumonia factors can affect urea, so that point cannot be interpreted outside the clinical context.
What the calculator actually does
- Confirms the adult, clinically diagnosed CAP entry.
- Reads the five values from the initial assessment.
- Normalizes BUN when needed.
- Applies the five fixed thresholds.
- Adds zero or one for each criterion and reports the validated total, NICE group, and audit.
It does not read records, confirm a chest image or pathogen, assess oxygenation, diagnose sepsis, shock or respiratory failure, calculate PSI or ATS/IDSA severe CAP criteria, or choose antibiotics, discharge, admission, ICU care, or another treatment.
CURB-65 and related CAP tools
NICE uses CRB-65 for adult primary/community assessment because it does not require urea, while CURB-65 is used in hospital adult CAP contexts. PSI/PORT is an independent multi-variable prognosis model; ATS/IDSA severe CAP criteria provide a different severe-CAP/ICU-support framework. None can be converted from the five inputs on this page. [2, 3, 4, 5]
| Tool | Intended context | Main inputs | Why it is not interchangeable |
|---|---|---|---|
| CURB-65 | Hospital adult CAP | Confusion, urea, RR, BP, age | This page calculates only the five-item model. |
| CRB-65 | Adult primary/community CAP | Confusion, RR, BP, age; no urea | It is a different four-item model; missing urea is not silently substituted. |
| PSI/PORT | Adult CAP prognosis and site-of-care support | Many demographic, comorbidity, examination and laboratory variables | It is an independent model and cannot be converted from CURB-65. |
| ATS/IDSA severe CAP criteria | Severe CAP/ICU-support assessment | Major and minor criteria with clinical judgment | This is not a five-point mortality-risk score and is not calculated here. |
Worked examples
- Score 0: no confusion, urea 7.0 mmol/L, RR 29.9/min, SBP 90 mmHg, DBP 60.1 mmHg, age 64 → Low. The strict boundaries are not outpatient or treatment instructions.
- Score 2: confusion Yes (+1) and BUN 19.7 mg/dL (normalized above 7, +1), with other criteria below threshold → Intermediate. BUN 19.6 mg/dL remains below the threshold under the exact conversion.
- Score 3: RR 30/min, DBP 60 mmHg, and age 65 → High. SBP/DBP together still contribute only one BP point.
The 19.6/19.7 mg/dL boundary uses the same published relationship—0.357 mmol/L per mg/dL BUN—while this implementation applies its reciprocal as 1 ÷ 0.357 ≈ 2.80112. This is a fixed software convention for the tested, unrounded comparison, not extra laboratory precision. [7]
These examples demonstrate frozen arithmetic and boundary behavior, not a patient-level probability, diagnosis, disposition, or treatment recommendation. [1, 2, 6]
Important limitations
CURB-65 does not include oxygen saturation or oxygen requirement, sepsis, shock, respiratory failure, rapid deterioration, multilobar disease, pleural complications, major comorbidity, frailty, functional status, social support, ability to take oral medication, pregnancy context, immunosuppression, or treatment response. Children need a pediatric pathway; HAP, VAP, COVID-19-specific pneumonia, and severe immunosuppression are not automatic page populations. A clinically unstable or urgent presentation should not wait for an online score. A low score does not exclude serious disease, and a high score does not automatically decide ICU or treatment. [2, 3, 6]
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. PMID 12728155. PMCID PMC1746657. DOI 10.1136/thorax.58.5.377.
- NICE NG250. Pneumonia: diagnosis and management. Published 2 September 2025; current recommendations page includes subsequent minor updates.
- Metlay JP, Waterer GW, Long AC, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. Am J Respir Crit Care Med. 2019;200(7):e45–e67. PMID 31573350. PMCID PMC6812437. DOI 10.1164/rccm.201908-1581ST.
- 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;336:243–250. PMID 8995086. DOI 10.1056/NEJM199701233360402.
- Aujesky D, Auble TE, Yealy DM, et al. Prospective comparison of three validated prediction rules for prognosis in community-acquired pneumonia. Am J Med. 2005;118(4):384–392. PMID 15808136. DOI 10.1016/j.amjmed.2005.01.006.
- Capelastegui A, España PP, Quintana JM, et al. Validation of a predictive rule for the management of community-acquired pneumonia. Eur Respir J. 2006;27(1):151–157. PMID 16387948. DOI 10.1183/09031936.06.00062505.
- Labcorp. SI Unit Conversion Table. Blood urea nitrogen (BUN): conventional mg/dL to SI mmol/L factor 0.357; SI to conventional factor 2.80.
FAQ
The original criterion is urea greater than 7 mmol/L. A public laboratory conversion table lists 0.357 mmol/L per mg/dL BUN; this implementation uses its reciprocal, 1 ÷ 0.357 ≈ 2.80112, as a fixed software convention before applying the original threshold without intermediate rounding. The convention preserves the tested boundary but does not claim extra laboratory precision or make displayed digits more exact.
No. The original threshold is strictly greater than 7 mmol/L.
Sources: [1]
NICE NG250 describes 0–1 as low, 2 as intermediate, and 3–5 as high hospital mortality-risk groups. They are population strata, not personal probabilities or automatic actions.
Sources: [2]
Related Calculators
PSI / PORT
Calculate the formal Fine 1997 two-step adult PSI/PORT class for established community-acquired pneumonia, with complete item and guideline limitations.
A–a Gradient
Calculate estimated alveolar oxygen tension and the alveolar–arterial oxygen gradient from FiO₂, arterial PaO₂ and PaCO₂, barometric pressure, and R.
Wells PE
Calculate the weighted Wells PE pretest-probability score with two-level and three-level classifications.
Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.