Blood Collection
General policy
The volume of blood removed and the time course over which that blood is removed are critical factors in determining acceptable blood collection regimens that minimize the effect of blood loss on the animal.
The volume of blood that can be collected without serious side effects is determined by the animals total blood volume. Most healthy animals can tolerate losing up to 15% of their total blood volume over a two-week period. Collection of volumes within this range will minimize hypovolemia and allow the animal to regenerate adequate numbers of erythrocytes before the next collection. Because fluid and electrolyte shifts between the intravascular and extravascular compartments occur fairly rapidly, fluid replacement is generally unnecessary as long as animals have free access to water and are able to drink easily.
Excessive frequency of blood collection may cause anemia or even hypovolemic shock. Calculation of total blood taken must include any blood that is not captured (i.e., additional uncollected drops) or remains in the needle or syringe.
The easiest way to determine the total blood volume for an animal is to follow the general principle that total blood volume is equivalent to 6% of the animals body weight
TOTAL BLOOD VOLUME (mls) = BODY WEIGHT (grams) X 0.06
For example, if 10 blood collection time points in a 300-gram rat were needed over a 24-hour period with 250 ul of blood to be taken per time point, the equation would be:
10 X 250 ul = 2500 ul or 2.5 ml blood needed
300 gms X 0.06 = 18 mls total blood volume 2.5/18 X 100 = 13.9% of total blood volume (acceptable amount)
For larger species, the same formula can be provided as:
TOTAL BLOOD VOLUME (liters) = BODY WEIGHT (kilograms) X 0.06
If the amount taken exceeds 15% for non-murine species or 25% for mice, additional justification is required. This may include a review of the literature documenting that adverse effects were not found when greater volumes were collected in this specific species and strain, under the same experimental conditions. Alternatively, a scientific justification may require higher volumes but include the provision of additional veterinary care, including close monitoring for signs of pain/distress and specific supportive care. Hematocrit (Packed Cell Volume) measurements should be taken at the end of blood collection when volumes above 15% are removed and the provision of intravenous fluids and iron injections should be considered.
Additional factors to consider in minimizing effects of blood loss include age, health status, genetic traits, and nutritional restrictions (e.g., low iron diet) or other components of the protocol (e.g., irradiation or pharmacological treatment) that may retard hematopoiesis. Such factors may require that less blood is taken at longer intervals than stated above or that parenteral fluids may be indicated immediately following blood collection to minimize the consequences of blood collection on the animals welfare.