WHO Functional Classification for Pulmonary Hypertension
The World Health Organization (WHO) Functional Classification for pulmonary hypertension categorizes patients into four classes based on symptom severity and physical activity limitations, which directly correlates with morbidity, mortality, and quality of life outcomes. 1
The Four WHO Functional Classes
Class I: Patients with pulmonary hypertension but without resulting limitation of physical activity. Ordinary physical activity does not cause undue dyspnea or fatigue, chest pain, or near syncope. 2, 1
Class II: Patients with pulmonary hypertension resulting in slight limitation of physical activity. They are comfortable at rest. Ordinary physical activity causes undue dyspnea or fatigue, chest pain, or near syncope. 2, 1
Class III: Patients with pulmonary hypertension resulting in marked limitation of physical activity. They are comfortable at rest. Less than ordinary activity causes undue dyspnea or fatigue, chest pain, or near syncope. 2, 1
Class IV: Patients with pulmonary hypertension with inability to carry out any physical activity without symptoms. These patients manifest signs of right heart failure. Dyspnea and/or fatigue may even be present at rest. Discomfort is increased by any physical activity. 2, 1
Clinical Significance and Prognostic Value
WHO functional class is one of the strongest predictors of survival in pulmonary arterial hypertension patients. 1, 3
Patients who improve from FC III to FC I/II have significantly better 3-year survival rates (84% ± 2%) compared to those who remain at FC III (66% ± 2%) or worsen to FC IV (29% ± 6%). 3
WHO-FC is a key determinant of prognosis, with Classes I and II associated with better outcomes compared to Classes III and IV. 2, 1
The functional classification directly influences medication choices and treatment intensity in pulmonary hypertension management. 1, 4
Monitoring and Assessment
WHO-FC should be assessed at baseline, every 3-6 months during stable disease, at initiation or changes in therapy, and in case of clinical worsening. 2, 1
Changes in functional class over time provide valuable information about disease progression or treatment response. 1, 3
Current guidelines recommend intravenous prostacyclin as first-line therapy for patients in FC IV, highlighting the importance of accurate classification. 5
For comprehensive patient evaluation, WHO-FC should be combined with other prognostic parameters such as exercise capacity (6-minute walk test), biomarkers (BNP/NT-proBNP), and hemodynamic measurements. 2, 1
Limitations and Considerations
The classification system can be subjective when assessed by clinicians, leading to potential variability in assessment. 6
Patients have reported challenges with the original WHO-FC terminology, including difficulty understanding clinical terms and overlapping descriptions between class II and III. 6
A patient self-reported version (PH-FC-SR) has been developed to allow patients to self-assess their functional status using more patient-friendly language. 6
Without appropriate treatment, PAH can rapidly deteriorate even in patients with less advanced disease states (WHO FC II). 4