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Guidelines for multiple blood draws

Veterinary Recommendations for Multiple Blood Draws – Volumes and Frequency

In many protocols, multiple blood draws are an important part of collecting and analyzing data. To help prevent problems associated with multiple blood collections, guidelines have been developed regarding the amount and frequency of blood collection. The aim of these guidelines is to reduce the risk of research related anemia, etc. and the affects these can have on experimental results.

There are several references that suggest the maximum amount of blood that can safely be drawn at a single survival blood draw is 1% of the animal’s body weight. If kilograms are used for the calculation, the volume result will be in liters.   To convert to mls, multiply the final answer by 1000. For example, a 25kg baboon can safely have 0.25 liters (or 250mls) of blood drawn at a single blood draw (1% or 0.01 x 25 = 0.25). If grams are used for the calculation, the volume result will be in milliliters. For example, a 200 gram rat can safely have 2 mls of blood drawn at a single blood draw (200 x 0.01 = 2).

If the recommended maximum blood draw is performed, there are several published suggestions on how much time should elapse between blood draws ranging from 2 weeks to 4 weeks. It only takes about 24 hours for the blood volume to be restored, but it can take a lot longer for the erythrocytes, platelets, coagulation factors, etc. to be replenished.  If the maximum amount of blood is drawn on one occasion, we recommend waiting about 3 weeks between blood draws to reduce the risk of anemia or other abnormalities. For experiments that do not require the suggested maximum blood draw, blood can safely be drawn more frequently.  The opposite also applies. If an experiment requires that blood is drawn and analyzed at certain time points, the guidelines can help determine the safe amount of blood that can be drawn at each time point.

Below is a table with guidelines that have been developed to assist investigators in their experiments. These guidelines are based on the amount of blood that is drawn and the frequency of blood collection.  Remember, the blood volume calculation will be in liters or milliliters, depending on the units of weight that are used (kg = liters, gm = mls).

Max blood draw (body weight)

Recovery time


3 weeks


2 weeks


1 week



Regarding the daily blood draw, this is the safe maximum per day that can be drawn. So, if there are several draws within one day, the safe maximum total amount of blood drawn in a 24 hour period is 0.05% of body weight.  For example, for a 7kg rhesus, the maximum amount of blood that should be drawn within 24 hours is 3.5mls (0.05% x 7).  If you need to test the blood every 8 hours, 1.7 mls of blood can be drawn each time. This will result in 3.5 mls drawn within 24 hours.

Another way to calculate the amount of blood that can be drawn is to use circulating blood volume. Circulating blood volume (CBV) is approximately 60ml/kg or 6% of body weight in kilograms or grams. When using 6% of body weight, the final result will be in liters if kilograms are used. To get mls, multiply by 1000. If grams are used, the final result will be in mls.

If using circulating blood volume (CBV), the maximum amount of blood that can be safely drawn at a single survival blood draw is 15% of CBV.  For example, a 200 gram rat will have a circulating blood volume of about 12 mls (60ml/kg x 0.2kg) or (0.06 (6%) x 200). 15% of the circulating blood volume would be 0.15 (15%) x 12 = 1.8 mls. This is the amount of blood that can safely be drawn at a single time and there should be 3 weeks in between blood draws of this volume.  Below is a table using circulating blood volume:

Max blood draw (CBV)

Recovery time


3 weeks


2 weeks


1 week



All research related blood draws must be fully detailed in an approved protocol or amendment. 

If you have questions about this guideline, please contact one of the clinical veterinarians at 410-955-3273.


1Removal of blood from laboratory mammals and birds. First report of the BVA/FRAME/RSPCA/UFAW joint working group on refinement. Laboratory Animals (1993) 27, 1-22.

2McGuill MW, Rowan AN. Biological Effects of Blood Loss: Implications for Sampling Volumes and Techniques. ILAR Fall 1989: 31(4) 5-18.

3Hoff J. Methods of Blood Collection in the Mouse. Lab Animal Nov 2000: 29 (10) 47-53.

4NIH Guidelines for Survival Bleeding of Mice and Rats.


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