CURB-65 Calculator
Score confusion, elevated urea, respiratory rate, blood pressure, and age for an adult already diagnosed with community-acquired pneumonia. Every point is exposed, U.S. BUN units are converted transparently, and emergency concerns sit outside the score as an override.
Complete all five checkpoints
CURB-65 result
Continue clinical assessment. A score never replaces evaluation of oxygenation, work of breathing, sepsis, organ dysfunction, or safe follow-up.
For adults with diagnosed CAP, 2019 ATS/IDSA guidance prefers the Pneumonia Severity Index over CURB-65 as an adjunct to clinical judgment when considering hospitalization. This result does not issue a disposition or antibiotic recommendation.
What CURB-65 is designed to do
CURB-65 is a five-item prognostic score developed for adults with community-acquired pneumonia. It compresses bedside and laboratory findings into a total from zero through five. The name is an acronym: Confusion, Urea, Respiratory rate, Blood pressure, and age 65 or older. Each criterion contributes one point; none is weighted more heavily.
The tool estimates severity at a population level after pneumonia has been identified. It does not diagnose pneumonia, distinguish bacterial from viral infection, select an antibiotic, identify sepsis, or determine whether a patient is safe at home. Chest imaging, oxygen saturation, history, examination, laboratory data, comorbidities, functional status, pregnancy, ability to take oral medication, and social support can all change a disposition decision.
Current U.S. ATS/IDSA community-acquired pneumonia guidance recommends a validated prediction rule plus clinical judgment for hospitalization decisions and preferentially recommends the Pneumonia Severity Index over CURB-65. CURB-65 remains simpler, which explains its common use, but simplicity is not evidence that its total is sufficient on its own.
The five exact checkpoints
Confusion
New disorientation to person, place, or time, or another defined mental-test abnormality. Chronic baseline cognitive impairment requires careful comparison with usual status.
Urea
Blood urea greater than 7 mmol/L. In U.S. BUN reporting, this is commonly represented as greater than about 19 mg/dL.
Respiration
Respiratory rate at least 30 breaths per minute. Count at rest rather than copying an unverified estimate.
Blood pressure
Systolic below 90 mm Hg or diastolic 60 mm Hg or lower. Either branch produces one point, not two.
Age
Age 65 years or older. Age contributes one point but does not capture frailty or physiologic reserve.
The BUN/urea distinction is a frequent U.S. data-entry problem. Many international studies report urea in mmol/L, while U.S. chemistry panels report blood urea nitrogen in mg/dL. This calculator divides BUN by 2.801 to show a urea equivalent and uses a BUN threshold greater than 19 mg/dL. Do not enter creatinine in the urea field.
Worked score of 3
Confirm purpose
A 72-year-old adult has clinician-diagnosed community-acquired pneumonia. The score is being used as one prognosis input.
Measure
There is no new confusion. BUN is 24 mg/dL, respiratory rate is 32, and blood pressure is 118/70.
Assign
Urea, respiratory rate, and age are positive. Confusion and blood pressure are negative. Total: 3.
Integrate
The higher score prompts urgent clinician-led assessment, but does not dictate an ICU bed, ward admission, or treatment.
The BUN converts to approximately 8.6 mmol/L urea, above the 7-mmol/L criterion. Respiratory rate 32 is at least 30. Age 72 is at least 65. Systolic pressure is not below 90 and diastolic is not 60 or lower, so the pressure criterion is zero.
This calculator deliberately does not attach a fixed mortality percentage to the score. Rates vary with cohort, care setting, inclusion criteria, treatment era, and calibration. A personalized percentage implied by a small integer would be misleading. The actionable message is to use a validated tool within a complete assessment.
Score bands are prompts, not placement orders
| Total | Educational interpretation | Required guardrail |
|---|---|---|
| 0–1 | Fewer CURB-65 risk features. | Does not prove outpatient care is safe; examine oxygenation, comorbidity, oral intake, follow-up, and red flags. |
| 2 | Intermediate number of risk features. | Needs prompt clinician-led site-of-care assessment; the score alone cannot choose observation or admission. |
| 3–5 | Higher number of risk features. | Urgent assessment and consideration of severe illness; use broader severe-CAP and organ-support criteria. |
A person can be critically ill with a low total. For example, severe hypoxemia is not a CURB-65 component. Neither are multilobar infiltrates, leukopenia, thrombocytopenia, hypothermia, fluid-requiring hypotension, mechanical ventilation, or vasopressor need. ATS/IDSA severe-CAP criteria and sepsis evaluation address different questions.
What the five checkpoints leave out
Oxygen and breathing work
Oxygen saturation, blood gas, baseline lung disease, accessory-muscle use, fatigue, and the amount of oxygen support are not in the total. Severe breathing difficulty warrants urgent care regardless of score.
Comorbid illness
Heart, lung, kidney, liver, neurologic, cancer, immune, and substance-use conditions can change risk and treatment. CURB-65 does not enumerate them.
Safe outpatient conditions
Ability to drink, take medicine, obtain prescriptions, understand instructions, return for worsening symptoms, and access follow-up can make outpatient management unsafe even with few points.
Diagnosis and etiology
The score does not confirm an infiltrate, identify influenza or COVID-19, detect pulmonary embolism, or decide whether antibiotics are indicated. Those require separate evaluation.
Data-quality and safety checklist
Use values from the same initial clinical assessment when possible. Repeat vital signs after stabilization are clinically valuable, but mixing a pretreatment BUN with a later respiratory rate can produce a score that never existed at one time. Record the time and whether oxygen, fluids, fever treatment, or other interventions occurred.
Confusion must be new or relevant to the acute illness. Baseline dementia, language barriers, hearing impairment, sedation, intoxication, and delirium from another cause complicate classification. Blood pressure needs an appropriate cuff and confirmation when unexpectedly low. Respiratory rate should be counted rather than estimated from appearance.
This module is limited to adults. Pediatric pneumonia uses different age-specific physiology and assessment. It is also not validated as a self-screening questionnaire for someone with a cough. If pneumonia is suspected, obtain medical evaluation rather than using a score to decide whether the illness exists.
Why a clinician may calculate PSI as well
The Pneumonia Severity Index collects more variables than CURB-65, including demographics, nursing-home residence, comorbid conditions, examination findings, laboratory data, and radiographic information. That longer input burden is one reason CURB-65 feels convenient, but the broader PSI evidence base is why ATS/IDSA preferentially recommends it when a prediction rule supports the hospitalization decision.
Neither rule replaces judgment. PSI can classify some older adults as higher risk largely because of age, while a young person with a dangerous feature outside CURB-65 can appear deceptively low. A responsible workflow first identifies immediate instability, then confirms diagnosis and severity information, applies a validated rule consistently, and finally tests whether outpatient care would be medically and practically safe.
Do not average CURB-65 and PSI totals or convert one into the other. They were derived differently and have different variables and classes. If the tools point in different directions, that disagreement is information for the treating clinician to resolve, not a reason to select the more reassuring score.
Frequently asked questions
Can CURB-65 diagnose pneumonia?
No. It is a prognostic rule for adults already diagnosed with community-acquired pneumonia. Symptoms, examination, imaging, and clinical judgment establish the diagnosis and evaluate alternatives.
Is BUN the same as urea?
No. BUN measures the nitrogen portion of urea and is commonly reported in U.S. mg/dL. The original criterion is urea greater than 7 mmol/L, often mapped to BUN greater than about 19 mg/dL.
Does a score of zero mean home treatment is safe?
No. Hypoxemia, comorbidities, inability to take oral treatment, rapid deterioration, social factors, or another diagnosis can require urgent or inpatient care despite zero points.
Why does U.S. guidance prefer PSI?
The 2019 ATS/IDSA guideline found stronger evidence for the Pneumonia Severity Index as an adjunct for hospitalization decisions. CURB-65 is simpler, but has less evidence for effectiveness and safety in that decision.
Does each low blood-pressure value add a point?
No. Systolic below 90 or diastolic 60 or lower together form one B criterion. Even if both are abnormal, the blood-pressure component contributes one point.
Can the score choose an antibiotic?
No. Antibiotic selection depends on diagnosis, severity, allergies, comorbidities, recent antibiotics, local resistance, microbiology, and current guidelines. CURB-65 contains none of that prescribing detail.
Related planning context
federal tax estimate. It has no role in determining pneumonia care or medical-expense eligibility.
References
- ATS/IDSA Guideline for Diagnosis and Treatment of Adults with Community-Acquired Pneumonia
- ATS/IDSA Community-Acquired Pneumonia Executive Summary
- Lim et al.: Defining community acquired pneumonia severity on presentation to hospital
- CURB-65 pneumonia severity assessment adapted for electronic decision support
Educational use only. Guidelines and local pathways change; use current clinician and institutional guidance.