Massive hemoptysis, also called life-threatening hemoptysis, means coughing up blood from the lower respiratory tract in an amount or at a rate that threatens life, mainly by blocking the airways and causing respiratory failure or asphyxiation.

There is no single universal volume cutoff. Published thresholds range from about 100 to 1,000 mL in 24 hours. A commonly cited definition is 500 mL of expectorated blood within 24 hours, but the practical definition is more important:

It is a medical emergency. Death is often due to blood filling the airways rather than blood loss alone. Common causes include bronchiectasis, tuberculosis or other severe infection, lung cancer, and less commonly vascular or clotting disorders. The immediate priorities are protecting the airway, maintaining oxygenation, localizing the bleeding source, and often bronchial artery embolization.

Murray & Nadel's Textbook of Respiratory Medicine notes 500 mL/24 hours as a commonly used criterion. Recent reviews also emphasize a functional, life-threatening definition rather than relying only on volume. A 2025 systematic review of bronchial artery embolization is indexed as PMID 41286932.