A cutting-edge measurement method, pulse oximetry, allows oxygen saturation levels to be measured without having to take blood samples. Conclusions about oxygen saturation levels can be made on the basis of the colour of the blood:
Light red: high oxygen saturation
Dark red: low oxygen saturation
In pulse oximetry, two light sources with different wavelengths are used to determine the oxygen saturation in arterial blood. Coloured nail varnish may interfere with the oxygen saturation measurement as the light sources may be unable to penetrate the varnish.