End-expired air technic for determining occupational carbon monoxide exposure.

Fluctuating carbon monoxide (CO) levels in the ambient air and recent smoking can lower the accuracy of the end-expired air sampling technic in COHB estimation, which involves the calculation of a regression equation relating measured carboxyhemoglobin (COHb) levels to CO levels in end-expired air after breathholding. Data collected under both laboratory and field conditions using this technic are presented in this study to suggest that, for increased accuracy of COHb estimation, researches should allow volunteers who have just smoked or are working in an atmosphere of fluctuating ambient CO levels to breathe a low CO atmosphere (less than 10 ppm) for at least two minutes before sampling, preferably an atmosphere close in CO level to that in which originally the blood and breath samples were collected to establish the regression equation.