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Single draw

Multiple draws

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Guidelines for Collection of Blood from Experimental Animals

Guidelines for safe blood withdrawal for laboratory mammals takes into account the fact that each different species has a different blood volume in milliliters of blood to kilogram of body weight.  They also assume a 14-21 day cycle for red blood cell renewal.  These guidelines are for normal, healthy adult animals. Animals that are aged, stressed, have undergone experimental manipulations, or are suffering from cardiac or respiratory disease may not tolerate this amount of blood loss. 


Blood collection may be performed adequately in awake animals of some species using the appropriate restraint. Restraint is necessary to prevent movement that may result in laceration of a blood vessel or other organ and serious complications. 

Dogs, Cats, Sheep and Calves usually require only physical restraint to collect blood. Appropriate instruction can be obtained from RAR at 624-9100. 


Rabbits and Swine - may require only physical restraint if they have been trained to the procedure. 

Rabbits, Mice and Rats - may be placed in appropriate restraining devices. Contact RAR at 624-9100 for assistance in selecting a restraint device. 

Chemical Restraint - may be used prior to blood collection to minimize distress to the animal and to the person doing the blood collection. Contact RAR at 624-9100 or see the Animal Care and Use Manual for information on anesthesia. 

Anesthesia is required to perform blood collection from the orbital sinus or by cardiac puncture because of the pain involved in the procedure and the potential for complications (including cardiac tamponade and death, or injury to the eye), even if performed by experienced personnel. Cardiac puncture is only approved for terminal blood collections unless specifically approved by the IACUC.
Procedural Guidelines

A table of common blood collection sites is given below.  Some sites required anesthesia because the procedures is painful.


Collecting blood by lacerating ear or tail vessels is prohibited. There is always the potential that an artery will be lacerated rather than a vein, resulting in severe hemorrhage. In addition, these procedures are more painful than puncture with a needle because of the prolonged time for wound healing. Also, the site of the procedure is very susceptible to infection, hemorrhage and other complications. Investigators can receive training in other methods listed below by contacting RAR at 624-9100. 

Regardless of the method of collection used, an animal may not be returned to its cage until complete hemostasis has been achieved (there is no more blood coming from the collection site). Hemostasis should be achieved using gauze and direct pressure. Up to several minutes of pressure may be required following arterial puncture. 

Single Blood Draw, Not Repetitive

As a one time large volume blood draw with concomitant IV fluid replacement, a maximum 2% of the body weight of a healthy adult animal can be removed, as long as fluid replacement consists of warmed, isotonic fluids and both the fluid replacement and blood withdrawal are slow and steady.

Single Blood Draw Repeated Multiple Times

For multiple blood draws separated by a period of weeks, a maximum of 1% of the animal's body weight can be removed, i.e., 0.15 ml from a 15 gram mouse; 50 ml from a 5 kg cat; 400 ml from a 40 kg dog. A 14 day recovery period is needed for the average healthy adult animal to recover from this blood loss. Although the blood volume is restored within 24 hours after blood withdrawal, two weeks Is needed for all constituents of the blood to return to normal. If less than the maximum amount of blood is withdrawn the animal will replace blood constituents at the rate of 1 ml/kg/day.

Multiple Blood Draws

If blood must be drawn more frequently than once every two weeks, a total of 0.5% of the animal's body weight can be removed each week with this total volume being spread out over the entire week if needed. 


By monitoring the hematocrit (or packed cell volume-PCV) and/or hemoglobin of the animal, it is possible to evaluate whether the patient has sufficiently recovered from a single blood draw or multiple blood draws. After a sudden or acute blood loss, it takes up to 24 hours for the hematocrit and hemoglobin to reflect this loss. This means that after a 1% of body weight blood loss without fluid replacement, an animal's hematocrit will not show a measurable drop for several hours, and will not stabilize for 24 hours. After 24 hours although the blood volume will normalize, the number of red blood cells (hematocrit) will be measurably reduced. In general, if the animal's hematocrit is less than 35% or hemoglobin concentration is less than 10 g/dl it is not safe to remove the volume of blood listed above. 

Terminal Blood Withdrawal

Terminal bleeds are only allowed on animals under full general anesthesia, and the animal's death must be verified at the end of the bleed. An alternative euthanasia method is recommended after the blood withdrawal. 

As a general rule:


An animal's blood volume is 10% of its body weight, and only half of that can be recovered when the animal is bled out. Therefore, as a terminal bleed, 5% of an animal's body weight is the blood volume (in ml) that may be recovered. 

Table 1 Common Sites for Blood Collection


Site of collection and permitted conditions
Mouse Cardiac (terminal only), orbital sinus (general or local anesthesia required), tail vein [note: incisional method not permitted], saphenous vein, facial vein, tail prick with 22g needle (or smaller) to obtain single drop of blood.
Rat As with mouse except facial vein is not used in rats. Subclavian and sublingual vein blood collection may be used in rats
Guinea Pig Cardiac (anesthetized only), anterior vena cava/subclavian vein
Rabbit Cardiac (anesthetized only), marginal ear vein
Dog, Cat & Nonhuman Primate Cephalic, saphenous, femoral and jugular veins
Ruminants Jugular vein
Swine Jugular vein, anterior vena cava, ear veins [Link to blood collection techniques]
Chicken Brachial wing vein, right jugular vein, cardiac (anesthetized only)

Table 2 Normal Packed Cell Volume (PCV) for some Laboratory Animals (%)

(Low end of given range is normal in juveniles, but not in adults) 
Dog 29-55 Rabbit 30-50
Cat 25-41 Guinea Pig 37-48
Rhesus 26-48 Hamster 40-61
Baboon 33-43 Rat 36-54
Swine 32-50 Mouse 39-49
Cow 24-48 Gerbil 43-60
Sheep 24-45


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The information contained in this site is intended as a reference for University of Minnesota investigators, and animal husbandry and veterinary staff. Drug information and dosages are derived from a variety of sources and do not necessarily guarantee safety or efficacy. Information obtained through this site should not be relied upon as professional veterinary advice. Any medications administered or procedures performed on animals should only be performed by or under order of a qualified, licensed veterinarian.