​​Why do doctors use Veins rather than Arteries to take blood samples?

Doctors can and do use arterial blood sampling but usually only when it is absolutely necessary ie. they need an arterial blood sample for arterial blood gas analysis (ABG) to find out how much oxygen and CO2 is in the arterial blood or when they cannot get venous access (for examples in trauma or otherwise seriously ill patients). Venous blood is preferred for number of reasons:

  • It is easier. Veins are superficial and there are lot of them. If you compress the arm proximally you can see and feel the veins running across the length of the upper limb. If you are taking arterial blood you usually go for the radial artery and you usually have to rely on the pulse you feel (or hear using doppler). Veins also tend to be more tethered if you pick the right spot ie the vein doesn’t wiggle away when you try inserting the needle and you don’t need to go fishing for it. Veins also have thinner walls which makes it easier to get a needle in. Novices (like myself) may need to use a bit more force to get into the artery and sometimes they push the needle right through the back wall in the process.

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