RESUMO
BACKGROUND: Methemoglobinemia and carbon monoxide poisoning are potentially life-threatening conditions that can present with nonspecific clinical features. This lack of specificity increases the probability of misdiagnosis or avoidable delays in diagnosis and management. These conditions are both treatable with antidotes of methylene blue and oxygen, respectively. Modern blood gas analyzers have the ability to measure carboxyhemoglobin (COHb) and methemoglobin (MetHb) levels without any additional resources. However, these results, although readily available from the machine used to perform the analysis, are not fully reported by some hospital clinical laboratories. CASE REPORT: A 49-year-old male presented with shortness of breath and cyanosis after inhaling cocaine via a nasal route ("snorting"). Methemoglobinemia was not initially considered in the differential diagnosis. However, the diagnosis of methemoglobinemia was made once newly routinely reported laboratory results revealed an elevated MetHb level. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Routinely reporting MetHb and COHb levels with arterial and venous blood gas results will facilitate making the diagnoses of these infrequently diagnosed causes of hypoxia more quickly so that early treatment of these uncommon but potentially lethal conditions can be initiated promptly.