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Prediction equations for single breath diffusing capacity (Tlco) in a middle aged caucasian population
  1. B R Thompson1,2,
  2. D P Johns3,
  3. M Bailey4,
  4. J Raven1,4,
  5. E H Walters3,4,
  6. M J Abramson1,4
  1. 1
    Allergy, Immunology and Respiratory Medicine, The Alfred Hospital, Melbourne, Victoria, Australia
  2. 2
    Department of Physiology, Monash University, Victoria, Australia
  3. 3
    Respiratory Research Group, Menzies Research Institute, University of Tasmania, Tasmania, Australia
  4. 4
    Department of Epidemiology and Preventive Medicine, Monash University, Victoria, Australia
  1. Dr B Thompson, Lung Function Laboratory, Allergy Immunology and Respiratory Medicine, The Alfred Hospital, Commercial Rd, Melbourne 3004, Victoria, Australia; b.thompson{at}


Background: There are many reference equations for the measurement of single breath carbon monoxide diffusing capacity of the lung (Tlco). However, the testing methodologies vary and there are no well documented studies that have developed reference equations for Tlco and alveolar volume (Va) in middle aged and older populations.

Aims: (1) Develop reference equations for Tlco in a middle aged population using the current American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines; (2) compare the equations with those commonly used in laboratories around the world.

Methods: Healthy subjects (498 male and 474 female) aged 45–71 years were recruited as part of a larger epidemiological study. All participants completed a respiratory questionnaire and had spirometry and single breath Tlco (corrected for haemoglobin) measurements following ATS/ERS guidelines.

Results: Mean age was 58 years for males and 57 years for females. For males, factors that predicted Tlco were: height, age, age×height interaction and being an ex-smoker. For females, factors that predicted Tlco were: height, age, weight and an age×height interaction.

Conclusion: We have described new prediction equations for Tlco in a middle aged population that require validation in other populations.

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  • Funding: National Health and Medical Research Council grant.

  • Competing interests: None.

  • Ethics approval: The study was approved by the ethics committee at The Alfred, Melbourne, Australia.