Finger tip<unk> yhemoglobin saturation monitor (SpCO%). Note: This is not the same as a pulse oximeter (SpO2%), although some models (such as this one) do measure both the oxygen and<unk><unk>  saturation. Breath CO monitor displaying<unk><unk>  concentration of an exhaled breath sample (in ppm) with its corresponding percent concentration of<unk> yhemoglobin. As many symptoms of<unk>  also occur with many other types of poisonings and infections (such as the flu), the diagnosis is often difficult. A history of potential<unk><unk>  exposure, such as being exposed to a residential fire, may suggest poisoning, but the diagnosis is confirmed by measuring the levels of<unk><unk>  in the blood. This can be determined by measuring the amount of<unk> yhemoglobin compared to the amount of hemoglobin in the blood. The ratio of<unk> yhemoglobin to hemoglobin molecules in an average person may be up to 5%, although cigarette smokers who smoke two packs per day may have levels up to 9%. In symptomatic poisoned people they are often in the 10–30% range, while persons who die may have postmortem blood levels of 30–90%. As people may continue to experience significant symptoms of CO poisoning long after their blood<unk> yhemoglobin concentration has returned to normal, presenting to examination with a normal<unk> yhemoglobin level (which may happen in late states of poisoning) does not rule out poisoning. Measuring<unk><unk>  may be quantitated in blood using spectrophotometric methods or chromatographic techniques in order to confirm a diagnosis of poisoning in a person or to assist in the forensic investigation of a case of fatal exposure. A CO-oximeter can be used to determine<unk> yhemoglobin levels. Pulse CO-oximeters estimate<unk> yhemoglobin with a non-invasive finger clip similar to a pulse oximeter. These devices function by passing various wavelengths of light through the fingertip and measuring the light absorption of the different types of hemoglobin in the capillaries. The use of a regular pulse oximeter is not effective in the diagnosis of<unk>  as these devices may be unable to distinguish<unk> yhemoglobin from oxyhemoglobin. Breath CO monitoring offers an alternative to pulse CO-oximetry.<unk> yhemoglobin levels have been shown to have a strong correlation with breath CO concentration. However, many of these devices require the user to inhale deeply and hold their breath to allow the CO in the blood to escape into the lung before the measurement can be made. As this is not possible in people who are unresponsive, these devices may not appropriate for use in on-scene emergency care detection of CO poisoning. Differential diagnosis There are many conditions to be considered in the differential diagnosis of<unk> . The earliest symptoms, especially from low level exposures, are often non-specific and readily confused with other illnesses, typically flu-like viral syndromes, depression, chronic fatigue syndrome, chest pain, and migraine or other headaches.<unk><unk>  has been called a "great mimicker" due to the presentation of poisoning being diverse and nonspecific. Other conditions included in the differential diagnosis include acute respiratory distress syndrome, altitude sickness, lactic acidosis, diabetic ketoacidosis, meningitis, methemoglobinemia, or opioid or toxic alcohol poisoning.
Carbon monoxide poisoning
Cyanide poisoning
Nitrogen dioxide poisoning
Upper respiratory tract infection
Chlorine gas poisoning
Alcoholic ketoacidosis
Salicylate poisoning
Theobromine poisoning