What is the difference between reading oxygen levels on an Oximeter and via an ABG blood test? Which is the best test or the best indication for INOCA patients?

The Oximeter reads the Oxygen saturation of circulating haemoglobin, that is the percentage of Hb bound to oxygen. ABG blood test provides much more detailed information on circulation arterial blood gases, including oxygen and Carbon dioxide concentrations, pH, Hb etc etc