Which of the following are necessary to ensure a valid single-breath diffusing capacity of the lungs (DLCO) test result?

1. Two or more acceptable tests should be averaged.
2. Breath-hold time should be between 3 and 5 sec.
3. Corrections for hemoglobin (Hb) and COHb should be included.
4. The maneuvers should be reproducible to within 10%.
a. 1, 2, and 3 only
b. 2 and 4 only
c. 1, 3, and 4 only
d. 1, 2, 3, and 4

ANS: C
The mean of two acceptable tests is the DLCO that meet the repeatability requirement of either being within 3 ml of CO (STPD)/min/mm Hg of each other or within 10% of the highest value.