The primary object of performing the test is to identify alveolar capillary membrane thickness. We have to find ways to make corrections for other variables.

• Corrected diffusion: Correction made for Hemoglobin
• DL/VA: Correction made for alveolar surface area.
• V/Q mismatch: If patient is obstructed we can assume there is a mismatch
• Capillary bed: We dont routinely evaluate this. If the lung volumes and flow indices are normal one should suspect a low diffusion as being secondary to reduced pulmonary vascular bed.

  In our patient the low diffusion is not corrected by Hemoglobin, there is no obstruction to consider V/Q mismatch and diffusion is low even when expressed by DL/VA. Hence the low diffusion in this patient is due to alveolar capillary membrane thickness.