What is carboxyhemoglobin, whole blood testing for in an arterial blood gas test, drawn from an arterial blood line? and what would an elevated count indicate?

If you mean “carbon-monoxyhemoglobin, it measures blood level of carbon monoxide

Carboxyhemoglobin is formed when carbon monoxide forms a stable bond with hemoglobin. Elevated levels may indicate exposure to carbon monoxide and exposure can be dangerous or fatal. Make sure that there is no exposure due to sources in the home or at work (malfunctioning heaters, engine exhaust, burning combustible materials). Carbon monoxide detectors are available and inexpensive.