Blood oxygen level?

There are several different ways. You could do a pulmonary function test with DLCO to calculate how well oxygen crosses from the lungs to the blood. You will blow in and out on a machine/computer.

They may do a pulse ox check. This is a probe on your finger what will estimate the % of oxygen on your blood. No blood is drawn.

They may do an ABG, a arterial blood gas will accurately show the pressure of oxygen in your blood. They will need to take some blood from an artery, usually from the wrist.

Or they may do all three.

Everyone here has been discussing oxygen saturation which should normally be more than 90%. However your friend may be referring to PaO2 or the partial pressure of oxygen in the blood which is a direct measure of oxygen in the blood taken from a sample of arterial blood. The normal level of PaO2 is 60-80 so 67 is right there. I don't think this 67% is referring to oxygen saturation because this would be a dangerously low level which would require intubation and mechanical ventilation. Your friend should speak to the doctor and find out exactly what this result means in the context of his case.

If you have venous insufficiendy, then that is a test they perform a doppler on your legs (a sonogram) of the veins. It is not a blood test. If they want to check your blood level, they can order a blood gas which will check you oxygen level specifically or a saturation which is another test they put a special transducer on your finger. The blood gas requires a needlestick to draw a small sample of blood.

all he will do is take a sample and analyse it in the lab, absolutely nothing to worry about!