Bluish skin is usually a sign of something serious. If normal color does not return when the skin is rubbed or warmed it is vital to seek the medical help.
Arterial Blood Gas Test: It measures the acidity and levels of carbon dioxide and oxygen in the blood.
Electrocardiogram: It is taken to completely the rule out the prevalence of cardiac abnormalities.
Chest X ray: It is taken to rule out the conditions like pneumonia, pulmonary infarction and cardiac failure.
Ventilation Perfusion Scan or Pulmonary Angiography: It is taken to rule out the pulmonary causes.
Echocardiography: It is used to look for the presence of any cardiac defects.
Haemoglobin Spectroscopy: The spectroscopy checks for the methemoglobinemia or sulfhemoglobinemia.
Digital Subtraction Angiography: It is done to completely rule out conditions like acute arterial occlusion.
Doppler or venography:
A duplex doppler or Venography can detect the prevalence of acute venous occlusion.