Most pneumonia cases can be treated at home with oral antibiotics, but roughly 20% to 30% of adults with community-acquired pneumonia need hospital care. The decision hinges on a combination of vital signs, blood work, age, and practical factors like whether you can keep medication down. Doctors use structured scoring systems to make this call, but certain red flags on their own can tip the balance toward admission.
How Doctors Score Pneumonia Severity
Emergency departments don’t rely on gut instinct to decide who stays and who goes home. Two validated scoring tools guide the decision: the CURB-65 score and the Pneumonia Severity Index (PSI).
The CURB-65 is the simpler of the two. It assigns one point for each of five factors: new confusion or disorientation, elevated blood urea nitrogen (a kidney function marker above roughly 20 mg/dL), a breathing rate of 30 or more breaths per minute, low blood pressure (systolic below 90 or diastolic at or below 60), and age 65 or older. The maximum score is 5, and each point dramatically changes the picture. A score of 0 or 1 carries about a 1.5% chance of dying within 30 days, and outpatient treatment is usually safe. A score of 2 bumps 30-day mortality to around 9%, putting you in a gray zone where a short hospital stay or close observation makes sense. At 3 or higher, the mortality risk reaches 22%, and inpatient admission is strongly recommended, with ICU-level care considered for scores of 4 or 5.
The Pneumonia Severity Index is more complex, factoring in age, sex, nursing home residence, coexisting illnesses, and lab results to sort patients into five risk classes. Classes I and II (30-day mortality under 1%) can safely go home. Class III (mortality up to about 2.8%) falls in a gray zone. Classes IV and V, with mortality rates of 4 to 10% and around 27% respectively, call for hospital admission.
Vital Signs That Trigger Admission
Certain numbers on a monitor can override even a low severity score. Oxygen saturation is the most watched. Patients whose blood oxygen dips below 90% are almost always admitted, but research shows that a threshold of 92% is safer and better justified. In a large population-based study, patients discharged with oxygen levels below 90% had a 6% mortality rate within 30 days compared to 1% for those with higher readings, and their rate of bouncing back to the hospital nearly tripled. Even patients who otherwise score as low-risk on the PSI should be admitted if they’re hypoxic, as an added margin of safety.
A breathing rate at or above 30 breaths per minute in adults is a standalone warning sign that appears in both the CURB-65 and the formal criteria for severe pneumonia. For context, a normal resting rate for adults is 12 to 20 breaths per minute, so 30 represents a significant jump that signals the lungs are struggling to keep up.
Low blood pressure requiring aggressive fluid resuscitation, a core body temperature below 36°C (96.8°F), and signs of confusion or disorientation also weigh heavily toward admission on their own.
When Pneumonia Qualifies as Severe
The American Thoracic Society and Infectious Diseases Society of America define severe community-acquired pneumonia using a specific checklist. Meeting even one major criterion, either septic shock requiring blood pressure medications or respiratory failure requiring mechanical ventilation, means ICU admission. Meeting three or more minor criteria also qualifies. The minor criteria include rapid breathing, low oxygen levels relative to supplemental oxygen, infection in multiple lung lobes, confusion, elevated kidney waste products, low white blood cell count (from the infection itself), low platelet count, abnormally low body temperature, and blood pressure that drops despite fluids.
This distinction matters because severe pneumonia isn’t just “worse pneumonia.” It’s a different clinical situation with different treatment timelines, a higher chance of complications like lung abscesses or fluid around the lungs, and often a need for IV antibiotics that can’t be given at home.
Age and Chronic Conditions Lower the Bar
Being 65 or older automatically adds a point on the CURB-65, but age alone isn’t the full story. Older adults often have conditions that make pneumonia harder to survive and more likely to spiral. In a large retrospective study of elderly pneumonia hospitalizations, cardiovascular disease (including heart failure and stroke history) was present in nearly 30% of cases. Diabetes appeared in about 11%, and chronic obstructive pulmonary disease in roughly 10%. Moderate to severe chronic kidney disease showed up in nearly 7%. Each of these conditions independently increases the risk of clinical deterioration once pneumonia takes hold.
Older adults also present differently. They’re less likely to spike a high fever and more likely to show confusion as the first or only obvious symptom. That atypical presentation can delay recognition, which is one reason clinicians tend to have a lower threshold for admitting elderly patients even when their initial numbers look borderline.
Children Have Different Thresholds
Pediatric pneumonia uses age-adjusted criteria because normal breathing rates vary dramatically by age. For infants aged 2 to 11 months, a breathing rate above 50 per minute is concerning. For children 1 to 5, the threshold drops to above 40. By age 5 and older, 30 breaths per minute in a child with fever raises a flag.
Hospitalization for children is generally recommended when oxygen saturation falls below 92%, when breathing rates exceed 70 in infants or 50 in older children, or when grunting, pauses in breathing, or nasal flaring are visible. Infants who can’t feed or who show grunting or apnea need inpatient care. Doctors also factor in whether caregivers at home can reliably monitor for worsening respiratory distress, a practical consideration that can be just as decisive as the clinical numbers.
Practical Factors That Affect the Decision
Sometimes the reason for admission has little to do with severity scores. If you can’t keep oral antibiotics down because of vomiting, you need IV medication, which means a hospital stay. Cognitive or functional impairment that would make it hard to take medications on schedule or recognize worsening symptoms also tilts the decision. Substance use disorders, homelessness, or living far from a medical facility all reduce the safety net that outpatient treatment depends on. These aren’t minor footnotes in the decision process. A technically treatable-at-home pneumonia becomes dangerous if the conditions for safe home care don’t exist.
Dehydration compounds the problem. Pneumonia increases fluid loss through rapid breathing and fever, and if you’re already unable to drink adequately, the combination can cause kidney stress and worsen the infection’s trajectory faster than antibiotics can work.
What Borderline Cases Look Like
The hardest calls involve patients who fall in the gray zone: a CURB-65 score of 2, a PSI class III, or someone whose numbers are technically okay but trending in the wrong direction. In these situations, many hospitals use observation units where you’re monitored for 12 to 24 hours, receive the first doses of antibiotics intravenously, and get reassessed. If your oxygen stays stable, you’re eating and drinking, and your breathing rate normalizes, you may go home with close follow-up.
If you’re evaluated for pneumonia and sent home, the signs worth watching for include worsening shortness of breath, persistent fever after 48 to 72 hours of antibiotics, inability to keep fluids down, chest pain that gets sharper with breathing, or new confusion. Any of these suggests the initial assessment may need revisiting.