Influence of Milk on Exhaled Carbon Monoxide (CO) Measurement by Portable CO Monitors.

Background: A portable breath carbon monoxide (CO) monitor has a high cross-sensitivity to hydrogen (H₂). This study examined the influences of H₂ after consuming milk on the detected CO values using three types of portable CO monitors.

Materials and methods: Exhaled breath from seven participants (four healthy nonsmokers and three smokers with otherwise unknown comorbidities) was collected in sampling bags. The participants then consumed 200 mL of milk, and the exhaled breath of each was collected in separate bags every 30 minutes until 9 hours later. CO and H₂ in the bag were measured using a gas chromatograph as a reference analyzer, and CO was also measured using three types of portable CO monitors.

Results: After consuming milk, H₂ levels were significantly higher, and CO levels were not significantly elevated as measured by the reference analyzer. However, CO levels in monitors A and B were significantly elevated, even though participants did not smoke. The H₂ levels in the reference analyzer significantly increased and reached a maximum 4.5 hours after consuming milk. The difference in CO levels between the reference analyzer and each monitor increased significantly after 5 or 5.5 hours.

Conclusions: This study suggested that the breath CO monitors with a cross-sensitivity to H₂ responded to H₂ as CO in the exhaled gas and measured higher than actual values after milk consumption. The extent of the influence of H₂ differed depending on the type of CO monitor. It is necessary to consider milk consumption when assessing the smoking status of people using portable CO monitors.