Butterfly needle technique refines drawing blood

7 years ago

In the Central Laboratory Animal Research Facility (GDL) of Utrecht University and the University Medical Centre Utrecht, an animal technician and a researcher together have developed a new technique for drawing blood from adult rats, using a butterfly needle instead of the usual abbocath (catheter and needle). As a result, the animals experience less discomfort.

The technique is described step by step below. Note that it may only be done by someone legally authorised to do it!

  1. The following items are laid out:
    1. a disposable washcloth
    2. 2 strong clothespins
    3. a 1-ml-syringe with 0.2 ml air in it
    4. a butterfly needle, 25G with tube, affixed to the 1-ml syringe
    5. an incubator (small box with a heating pad)
    6. temperature recording system incl. sensor (for in the incubator)
  2. The rat spends 10 to 15 minutes in the incubator to make its blood vessels clearly visible. The starting time is set to prevent errors. The temperature must be monitored constantly.
  3. The rat is laid in a disposable washcloth, with its tail sticking out. The edge of the washcloth next to the tail is rolled up tightly and secured using the clothespins. The rat can breathe through the thin washcloth.
  4. The tail is punctured with the butterfly needle and blood is drawn. This requires some practice, and it is best done when the rat is still warm.
  5. The clothespins are removed, after which the washcloth is taken from the rat and the rat is set back in its cage.


This method has several advantages. The most important is that the technique requires fewer procedures for the rat than using the abbocath (where the needle is removed and the catheter is pushed into the blood vessel). This limited handling requires no anaesthesia. In addition, with the butterfly needle it is immediately clear whether or not the right vessel has been hit, and blood flows into the tube even when it has only been inserted 1-2 mm. Furthermore, there is no ‘dead volume’ (the extra blood that needs to be drawn in order to keep a given quantity) as there is with the abbocath. Although wrapping the animal in the washcloth does produce some stress, it causes less discomfort than anaesthesia, especially after the procedure. The rat is generally calm again right away, while with anaesthesia it is uncomfortable for some time. The technique can be used on both females and males.

The new technique is specifically an improvement for experiments where blood must be drawn several times a day. The advantages with incidental use are less pronounced, and will partly depend on the experience of the person performing it. For this reason, the GDL uses both techniques concurrently.