Synopsis of the diffusing capacity of the lung for carbon monoxide (DLCO) skills workshop

Calibration, QC and settingsTechnical aspectsStandardisation of test performanceReporting and interpretation
  • Check ambient conditions (use a reliable barometer and thermometer)

  • Ensure the correct system settings for dead space, pressure range, volume, and BTPS correction

  • Accurate calibration for volume and pressure

  • Check volume accuracy ±75 mL

  • 0–90% response time ≤150 ms

  • Linearity: ≤0.5% of full scale

  • Accuracy: ±1% of full scale

  • Adjust for lag and response time

  • QC using regular biological controls

  • Quality assurance using syringe or DLCO gas simulator

  • Interference from 5% CO2 or 5% water vapour ≤10 ppm error in CO

  • Drift for CO ≤10 ppm over 30 s

  • Drift for tracer gas ≤0.5% of full scale over 30 s

  • BHT 10±2 s

  • Maximum time for unforced exhalation to RV is ≤12 s

  • Vinsp target of ≥90% of largest VC in same lung function testing session

  • Vinsp ≥85% of VC is acceptable if VA is within 200 mL or 5% of highest VA from acceptable DLCO trial

  • Vinsp must be <4 s, longer Vinsp must be noted on report

  • Exhalation post-BHT past sample collection on classic systems <4 s

  • Exhalation to RV post BHT on RGA systems can be up to 12 s

  • Between test wait time: 4 min, 10 min for patient with severe airflow obstruction (on RGA, check tracer gas concentration at end-exhalation ≤2% of the inspired concentration)

  • Must remain seated during wait time

  • Recommended to check end-exhalation CO levels prior to inhalation of test gas; this can be used to adjust to the test for CO back-pressure and calculate COHb; allows compensation for water vapour and CO2 effects

  • Repeatability requirement: there must be at least two acceptable manoeuvres that are within 2 mL·min−1·mmHg−1 (0.67 mmol·min−1·kPa−1) of each other

  • Record when last cigarette was smoked

  • Always use DLCO corrected for Hb and COHb where applicable

  • Clearly state if no recent Hb is available

  • Report the grading of the DLCO manoeuvres

  • Record altitude

QC: quality control; BTPS: body temperature and pressure, saturated; BHT: breath-holding time; RV: residual volume; Vinsp: inspiratory volume; VC: vital capacity; VA: alveolar volume; RGA: rapid gas analyser; COHb: carboxyhaemoglobin; Hb: haemoglobin.