Cooximetry

Cooximetry is a laboratory technique that measures the concentrations of different forms of hemoglobin in blood using multiwavelength spectrophotometry. A co-oximeter analyzes a blood sample at multiple light wavelengths and applies algorithms to separate the overlapping spectra of oxyhemoglobin (HbO2), deoxyhemoglobin (HHb), carboxyhemoglobin (HbCO), and methemoglobin (MetHb), and sometimes sulfhemoglobin. Results are reported as fractional concentrations and percentages of total hemoglobin, and oxygen saturation is calculated from HbO2 relative to total Hb.

Specimens are typically arterial or venous blood that is heparinized and analyzed promptly to minimize changes in hemoglobin species. Cooximetry is often integrated into blood gas analyzers or used as a dedicated instrument in hospital laboratories and some point-of-care devices.

Clinical use and interpretation: Cooximetry is essential for diagnosing and monitoring conditions that alter hemoglobin species, such as carbon monoxide poisoning (HbCO), methemoglobinemia (MetHb), and sulfhemoglobinemia (sulfhemoglobin). It also provides information on total hemoglobin and helps assess oxygen delivery and the adequacy of treatment in critical care settings.

Limitations: Accuracy can be affected by dyshemoglobins beyond HbCO and MetHb, sulfhemoglobinemia, bilirubin, lipids, or hemoglobin variants. Sample quality, instrument calibration, and maintenance influence results. Cooximetry complements pulse oximetry, which cannot distinguish HbCO or MetHb, whereas co-oximetry provides specific measurements of these species.