Light's Criteria

Light's criteria are a set of laboratory rules doctors use to tell what kind of fluid has built up around the lungs. By comparing protein and an enzyme called LDH in the fluid against levels in the blood, they classify a pleural effusion as either an exudate, from inflammation, infection, or cancer, or a transudate, from pressure imbalances like heart failure. An exudate points toward more serious local causes that need further investigation.

Origin

Named for Dr. Richard W. Light, the American pulmonologist who published the criteria in 1972. They remain the standard first step in evaluating pleural fluid worldwide.

Significance in Asbestos Context

When fluid collects around the lung in someone with possible asbestos disease, Light's criteria help sort out whether the cause is likely serious, such as mesothelioma. An exudative result prompts further testing, including cytology and often biopsy, to look for cancer cells. The classification is recorded in the medical chart and marks the diagnostic path that led to a mesothelioma finding. Ask whether your effusion was exudative and what follow-up testing was done.

Example Sentence

Her pleural fluid met Light's criteria for an exudate, prompting the cytology and biopsy that revealed mesothelioma.

Related Terms

Pleural Effusion, Thoracentesis, Exudate, Pleural Fluid Cytology, Malignant Pleural Effusion

Notes

• Ask whether your pleural fluid was classified as an exudate or a transudate, and why.
• An exudative effusion warrants cytology and often biopsy; ask what follow-up is planned.
• Keep the pleural fluid lab reports; they document the diagnostic workup.