Drawing blood from rodents is necessary for a large number of both in vitro and in vivo studies. Sites of blood draws are numerous in rodents: retro-orbital sinus, jugular vein, maxillary vein, saphenous vein, heart. Each technique has its advantages and disadvantages, and some are not approved any more in some countries (e.g., retro-orbital draws in Holland). A discussion of different techniques for drawing blood are available 1-3 . Here, we present two techniques for drawing blood from rats, each with its specific applications.
Blood draw from the saphenous vein, provided it is done properly, induces minimal distress in animals and does not require anesthesia. This technique allows repeated draws of small amounts of blood, such as needed for pharmacokinetic studies 4,5 , determining plasma chemistry, or blood counts 6 .
Cardiac puncture allows the collection of large amounts of blood from a single animal (up to 10 ml of blood can be drawn from a 150 g rat). This technique is therefore very useful as a terminal procedure when drawing blood from the saphenous would not provide a large enough sample. We use cardiac puncture when we need sufficient amounts of serum from a specific strain of rats to grow T lymphocyte lines in vitro 4-9 .
Download video file. (29M, mp4)Note: All procedures must be approved by your institute's animal care and use committee.
This procedure is performed without anesthesia and requires two persons, one who handles the rat, and one who performs the draw.
Make a cone out of a towel or hold the rat with rodent handling gloves, leaving one hind limb exposed.
Shave the back of the leg with an electric trimmer until the saphenous vein is visible. Shave a large enough area, so that no hair will come in contact with the puncture site. Use a small amount of non-fragrant hand lotion to keep the non-shaved hair away from the puncture site.
Make a compression point at the base of the leg to make the saphenous vein bulge out (similar to using a tourniquet when drawing blood from a human or a large animal). Puncture the vein using a 20G needle and scoop the blood as it comes out using a microvette. Pumping with the leg will help draw more blood. When you have collected enough blood, hold a clean compress on the puncture site to stop bleeding.
This procedure requires anesthesia and is terminal. Animals must immediately be euthanized at the end of a cardiac puncture.
Prepare a 5 ml syringe with a 23G1 needle.Deeply anesthesize the rat and check for anesthesia by lack of spontaneous movement, slow breathing rate, and lack of response to stimuli (such as pinching a toe). To ensure prolonged anesthesia, place a syringe barrel containing paper towel soaked in volatile anesthetic on the rat's nose during the procedure.
Place the rat on its back, facing away from you.If you are right-handed, place your left index finger at the level of the lowest ribs, without applying any pressure. The heart will be located ~ 1 cm above this point, slightly to the right.
Holding your syringe at a 45-degree angle, insert the needle between two ribs and watch for a drop of blood to come into the needle. This is an indication that you are in the heart. Without moving your syringe, pull on the plunger to fill the syringe. Once the syringe is full, carefully disconnect it from the needle and empty it into a tube. The syringe can then be re-attached to the needle for drawing more blood. It should be possible to draw 5-10 ml of blood from a 120-180 g rat.
Immediately euthanize the rat.Drawing blood from the saphenous vein is a convenient way to get small amounts of blood without anesthesia. If repeated sampling is required, check regulations to ensure you do not draw too much blood from one rat.
Drawing blood by cardiac puncture is a convenient way to get large amounts of blood but this is a terminal procedure. The animal must be euthanized at the end of the blood draw.
These techniques (as all techniques on live animals) should be first done in the presence of a veterinarian or a veterinary technician who will be able to assess that animals are handled properly and are not subjected to unnecessary pain and/or distress.
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