Decision tree

How much blood does a rat have?

On average, rats have around 64 ml of blood per kg of bodyweight.

A rat weighing 400 g would therefore have a total blood volume (TBV) of approximately 64 ml/kg x 0.4 kg = 25.6 ml.

How to decide on the most appropriate blood sampling technique for rats?

The two tables below are designed to assist in determining the amount of blood to sample from the animal, and depending on that volume, the most appropriate techniques to use.

1. Do you require more than one blood sample from the same rat?



Maximum <10% TBV (= 2.56 ml) on any single occasion AND <15% TBV (= 3.84 ml) in 28 days

Maximum <10% TBV (= 2.56 ml)

For repeat bleeds at short intervals, suggested limit <1% TBV (= 0.25 ml) in 24 hours AND consider cannulation

OR terminal sample under general anaesthesia (volume unrestricted)


2. How much blood do you require?

Total of <3.0 ml

Total of >3.0 ml

General anaesthesia required

General anaesthesia not used

General anaesthesia required; non recovery

Saphenous vein

Tail vein

Sublingual vein*


Sapenous vein

Tail vein / Temporary cannula

Jugluar vein

Blood vessel cannulation**

Cardiac puncture

Abdominal / thoracic blood vessel


Decapitation #

* Not widely used (Zeller et al. 1998)
**Cannulation surgery performed under general anaesthesia.
# Blood may be mixed with tissue fluid.