Why can't blood samples be taken from the legs/ankles as well arms/wrists?

Question

This is a genuine question, which so far I've been unable to find an answer to.

Some time ago when my wife was pregnant, she seemed to be constantly needing to have samples taken for various tests etc. My wife is very petite, and it was an enduring problem for them to find a suitable vein to take the sample.

On one such occasion, after having watched my wife endure jab after jab from the nurse trying to find a vein that was big enough, I asked...

"Is it possible to take the sample from a different place, like her ankles?"

The veins on the ankles are larger, and more prominent, and it seemed a perfectly logical choice to me.

The nurse gave me an almost horrified look as she quickly answered "No!". She didn't give any kind of reason as to why this was not possible. It was almost like she was embarrassed that I'd even asked such an (apparently) absurd question.

So my question is, is there some actual reason why the ankles are not a suitable location? Some thoughts I've had...

• Perhaps it effects the quality of the sample. I figured blood was blood, but I could be wrong.

• Perhaps it could cause extra bleeding afterwards. This certainly seems like it could be possible, but should be easy enough to manage, by applying the cotton bud more firmly, keeping the patient lying down for longer etc.

• Perhaps it's more painful? I can't imagine why though, I'm fairly sure that ankles are no more sensitive than wrists.

Answer 1

Blood is not always drawn from the veins depending on the medical need and situation. In most of the cases and for general tests, however, blood is drawn from veins which is known as Venipuncture. (Why draw blood from veins rather than arteries?

The integrity of the sample taken is dependent on using good technique, drawing from an appropriate site, and avoiding hemolysis or contamination of a sample.Link

Site selection for venipuncture

Factors to be considered for site selection:

1. Condition of the Superficial Veins
2. Relationship of the Vein to other Anatomic Structures
3. Duration of the Venipuncture
4. Clinical Status of the Patient
5. Age (Size) of the Patient

Characteristics of good veins for venipuncture include bouncy, soft, refills when depressed, has a large lumen, straight, visible and is well supported.

Veins to avoid during venipuncture

• Veins that may be irritated from previous use
• Veins in lower extremities
• Areas of joint flexion
• Veins close to arteries and deeper-lying vessels

The antecubital area of the arm is usually the first choice for routine venipuncture. This area contains the three vessels primarily used by the phlebotomist to obtain venous blood specimens: the median cubital, the cephalic and the basilic veins. Although the veins located in the antecubital area should be considered first for vein selection, there are alternate sites available for venipuncture. These include the top of the hand, the side of the wrist, and the forearm. These sites should only be considered after determining that the veins of the antecubital area cannot be accessed or cannot be used.Link

In practice, the usual preference is the arm, with the leg used when arm veins are inadequate or in emergency situations in which the arm may be unavailable or unsuitable for use.

Use of the leg for venipuncture is usually reserved for the infant or child, in whom arm veins are smaller and less superficial than in the adult, or the adult with a disability, in whom a venipuncture site in the foot may be more easily secured than one on the arm.

Advantages of the foot or ankle for venipuncture include the following:

1. Superficial vessels
2. Relatively large vessels
3. Anatomically safe
4. No need to immobilize the venipuncture site

Disadvantages of the foot and ankle as a venipuncture site include the following:

1. Accessibility is more limited than with the upper limb.
2. Veins roll when contacted by the needle.Link

In the case of difficult venipuncture, an individual may make a maximum of two attempts before having someone else try. A third stick is allowable if a partial sample has been obtained and you as the drawer feel reasonably confident that you can obtain the specimen on the next try.Link