Total Lung Capacity (TLC)
- Sample Type
- Standard
- Fasting
- No
- Unit
- Liters
Total Lung Capacity (TLC) is the volume of air contained in the lungs at the end of a maximal inspiration. In a Pulmonary Function Test (PFT), TLC is the gold standard for diagnosing restrictive lung diseases. While spirometry (FVC/FEV1) suggests restriction, a measurement of TLC (via plethysmography or gas dilution) is required to confirm it. It helps differentiate between intrinsic lung diseases (like pulmonary fibrosis) and extrinsic factors (like chest wall deformities or obesity).
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Why Context Matters
TLC measurements are effort-dependent. If the patient does not perform a maximal inspiration, the TLC will be falsely low. Furthermore, in patients with severe airway obstruction (COPD), gas dilution methods may underestimate TLC compared to body plethysmography because they cannot measure 'trapped' air, potentially leading to an incorrect diagnosis.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Total Lung Capacity (TLC):
Official Sources
Research & Guidelines
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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