Pseudoelevation of carboxyhemoglobin levels in firefighters

Carbon monoxide is a common and potentially lethal exposure documented by an elevated carboxyhemoglobin (COHb) level. We conducted an investigation of unexpectedly high carboxyhemoglobin levels in a group of firefighters. Twelve of 34 (35%) nonsmokers tested had levels greater than 4% COHb and 9 of 34 (26%) had levels of 10% or higher. Quadruplicate blood samples from hospital staff and firefighters were sent in duplicate to the original laboratory, which used manual spectrophotometry, and to a second reference facility using a cooximeter. Cooximeter results were lower and also more reproducible. By cooximetry, all 24 nonsmoking firefighters retested had COHb levels less than 3%. Cooximetry is widely available and is the most suitable methodology in clinical situations. Spurious results despite the use of a large reference laboratory argue for the standardization of analytic methods for COHb among laboratories.