Reference — Pulmonary Diseases
Pulmonary Disease Severity Classifications
The staging systems an RT is expected to recognize across the common pulmonary diseases — COPD GOLD grades, asthma severity and control, the ARDS Berlin definition, and CURB-65 for pneumonia — gathered in one scannable reference.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
Each major pulmonary disease has its own severity language, and the cutoffs come up on board exams and on rounds. They are not interchangeable: COPD is graded by spirometry, asthma by both intrinsic severity and current control, ARDS by an oxygenation ratio measured under a defined PEEP, and community-acquired pneumonia by a simple point score that drives disposition. These same thresholds underlie the comparison charts elsewhere on the site.
COPD — GOLD Spirometric Grades
| Grade | Post-bronchodilator FEV₁ | Severity |
|---|---|---|
| GOLD 1 | ≥80% predicted | Mild |
| GOLD 2 | 50–79% predicted | Moderate |
| GOLD 3 | 30–49% predicted | Severe |
| GOLD 4 | <30% predicted | Very severe |
Grades apply only once a post-bronchodilator FEV₁/FVC <0.70 confirms persistent airflow limitation. The GOLD grade (airflow) and the A/B/E group (symptoms and exacerbation risk) are separate axes — the group, not the grade, drives the drug regimen.
Asthma — Severity & Control
| Severity | Typical Pattern |
|---|---|
| Intermittent | Symptoms ≤2 days/week; no interference with activity; rare night waking |
| Mild persistent | Symptoms >2 days/week but not daily; minor limitation |
| Moderate persistent | Daily symptoms; daily reliever use; some activity limitation |
| Severe persistent | Symptoms throughout the day; frequent night waking; activity is limited |
| Control Level | GINA Criteria (past 4 weeks) |
|---|---|
| Well controlled | None of the four control features present |
| Partly controlled | 1–2 control features present |
| Uncontrolled | 3–4 control features present |
The four GINA control features (past 4 weeks): daytime symptoms more than twice/week, any night waking from asthma, reliever needed more than twice/week, and any activity limitation. Severity is judged retrospectively by the treatment required to maintain control.
ARDS — Berlin Severity
| Severity | PaO₂/FiO₂ (on PEEP/CPAP ≥5 cm H₂O) |
|---|---|
| Mild | 200 < PaO₂/FiO₂ ≤ 300 |
| Moderate | 100 < PaO₂/FiO₂ ≤ 200 |
| Severe | PaO₂/FiO₂ ≤ 100 |
All categories also require onset within one week of a known insult, bilateral opacities not fully explained by effusion/collapse/nodules, and respiratory failure not fully explained by cardiac failure or fluid overload. The 2023 global definition broadens recognition to include patients on high-flow nasal oxygen (≥30 L/min) and an SpO₂/FiO₂ ratio, extending the syndrome beyond intubated ICU patients.
Pneumonia — CURB-65
| Criterion (1 point each) | Threshold |
|---|---|
| Confusion | New disorientation in person, place, or time |
| Urea | BUN >19 mg/dL (urea >7 mmol/L) |
| Respiratory rate | ≥30 breaths/min |
| Blood pressure | SBP <90 mm Hg or DBP ≤60 mm Hg |
| Age | ≥65 years |
Disposition by total score: 0–1 low risk (usually outpatient), 2 consider short-stay admission, 3–5 severe — assess for ICU care. CURB-65 grades severity; it does not replace clinical judgment or oxygenation assessment.
Clinical Notes
- COPD is graded post-bronchodilator. Grade the airflow limitation on spirometry after a bronchodilator, and keep the GOLD grade separate from the A/B/E group that actually sets therapy.
- Asthma severity and control are different questions. Severity is the intrinsic disease (judged by the treatment needed); control is how the patient is doing right now. Both are tracked, and they can diverge.
- ARDS P/F is meaningful only at PEEP ≥5. The same ratio measured at low or zero PEEP overstates severity; always read the PaO₂/FiO₂ together with the set PEEP.
- These cutoffs feed the comparison charts. The COPD-vs-asthma, obstructive-vs-restrictive, and ARDS-vs-cardiogenic-edema charts all rest on the thresholds collected here.
Related Resources
Sources
- Global Initiative for Chronic Obstructive Lung Disease. Global Strategy for Prevention, Diagnosis and Management of Chronic Obstructive Pulmonary Disease (current annual report). GOLD.
- Global Initiative for Asthma. Global Strategy for Asthma Management and Prevention (current annual report). GINA.
- ARDS Definition Task Force; Ranieri VM, Rubenfeld GD, Thompson BT, et al. Acute respiratory distress syndrome: the Berlin definition. JAMA. 2012;307(23):2526-2533.
- 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 (CURB-65). Thorax. 2003;58(5):377-382.
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.