Cyanosis - if it existed - would be readily apparent even if they were not looking for it. It is a visible thing, hard to miss.
That being said, you don't get cyanosis from carbon monoxide poisoning.
Cyanosis is also observed when a chemical agent blocks the ability of hemoglobin to bind oxygen. For example, carbon monoxide, CO, a product of incomplete combustion, binds to hemoglobin approximately 200 times better than oxygen. Victims of carbon monoxide poisoning often have blue lips and fingernails.
The MSDS HyperGlossary: Cyanosis
Entry in the Material Safety Data Sheet HyperGlossary at ILPI.
www.ilpi.com