Letters to the Editor e NON-INVASIVE PULSE CO-OXIMETERY: WHAT IS MEASURED? e To the Editor: I read with interest the article by Suner and colleagues describ- ing use of a non-invasive pulse CO-oximeter for rapid screening for “CO (carbon monoxide) toxicity” in a high-volume, urban emergency department (1). I com- mend the authors for the size of their clinical trial but contend that the study was actually using the SpCO mea- sured by the device to screen for elevated carboxyhemo- globin (COHb) levels. Although this may be an issue of semantics, it should be clarified that the device does not measure any index of actual toxicity from CO. Secondly, the finding of an unexpectedly elevated COHb level should not be automatically equated with occult CO toxicity or poisoning. In addition to elevation by exogenous exposure to the gas, endogenous production from hemoglobin degradation results in the low levels of COHb that are seen even in non-smokers, and accelerated turnover of hemoglobin, such as occurs in hemolysis, can also raise COHb ( 2). It is important to remember this when doing population screening in individuals without clinical suspicion for CO poisoning, as the incidence of such an alternate explanation for an abnormal measurement may be higher. Neil B. Hampson, MD Virginia Mason Medical Center Seattle, Washington doi:10.1016/j.jemermed.2008.03.048 REFERENCES 1. Suner S, Partridge R, Sucov A, et al. Non-invasive pulse CO- oximetry screening in the emergency department identifies occult carbon monoxide toxicity. J Emerg Med 2008;34:441–50. 2. Hampson NB. Carboxyhemoglobin elevation due to hemolytic ane- mia. J Emerg Med 2007;33:17–9. e REPLY: ELEVATED SpCO IS MOST COMMONLY FROM AN EXOGENOUS SOURCE OF CARBON MONOXIDE e To the Editor: We thank Dr. Hampson for his comments in his letter to the editor. Although in the overwhelming majority of cases that present to the emergency department, the elevated carboxyhemoglobin (COHb) is a result of ex- ogenous carbon monoxide (tobacco or otherwise), our title did not specify the source of carbon monoxide toxicity. In our cohort, the patients with elevated SpCO, which was confirmed with COHb measurements, all had exposure to CO (carbon monoxide). There were no cases of hemolysis or other endogenous sources of CO in this group. As Dr. Hampson points out, the differential diag- nosis of elevated COHb or SpCO levels should include endogenous as well as exposure to exogenous sources of CO. It also should be pointed out there is no established and verified index of actual toxicity from CO. It is well known that there are delayed manifestations of CO tox- icity in addition to acute signs and symptoms from CO exposure; therefore, any study that evaluates population screening for COHb will suffer from lack of an objective definition of CO toxicity. Selim Suner, MD, MS Department of Emergency Medicie Department of Surgery Warren Alpert Medical School at Brown University Providence, Rhode Island Department of Emergency Medicine Rhode Island Hospital Providence, Rhode Island Division of Engineering Brown University Providence, Rhode Island doi:10.1016/j.jemermed.2008.06.035 e SENSITIVITY OF SCREENING TESTS AND OTHER QUESTIONS e To the Editor: We were quite interested to read the results reported by Dr. Suner et al. regarding their use of a non-invasive carboxyhemoglobin detector (RAD-57, Masimo Corp., Irvine, CA), given that our experience with the device was very different from theirs (1). Dr. Suner and his colleagues describe the sensitivity of the carboxyhemoglobin detection device as 94%, but we believe this is incorrect. Although the authors en- rolled over 10,000 patients in the study, they actually The Journal of Emergency Medicine, Vol. 37, No. 3, pp. 310 –312, 2009 Copyright © 2009 Elsevier Inc. Printed in the USA. All rights reserved 0736-4679/09 $–see front matter 310