Question 1

What factors determine which blood withdrawal method to use in mice and rats?

Accepted Answer

Blood withdrawal method selection depends on four key factors: the volume of blood needed, frequency of sampling, the animal's health status, and the technician's skill level. These considerations ensure the procedure is safe, effective, and appropriate for the specific research requirements. Different methods—retro-orbital, tail snip, and intracardiac—suit different experimental needs.

Question 2

What is the difference between plasma and serum in blood samples?

Accepted Answer

Plasma is collected from whole blood with anticoagulant and contains fibrinogen and clotting factors. Serum is collected from whole blood without anticoagulant; after clotting, the top layer lacks fibrinogen and clotting factors. The choice depends on experimental requirements, as each sample type has distinct biochemical properties and applications.

Question 3

Why is needle selection important for blood collection in rodents?

Accepted Answer

Needle selection depends on animal size and venipuncture site. Large bore needles cause less blood cell damage and enable rapid collection but risk vessel damage. Needle length matters too—if too long, blood may clot inside the needle. Appropriate sizes range from 18 to 29 gauge and 0.5 to 1.5 inches, with specific sizes recommended for each collection method.

Question 4

How is the retro-orbital bleeding technique performed in mice?

Accepted Answer

After anesthetizing the animal with inhalation anesthetic, place it in lateral recumbency. Pull skin back along the jaw to induce eye protrusion. Insert a micro-hematocrit tube into the medial canthus at 30-45 degrees, rotating gently to rupture the ocular sinus. Blood flows by capillary action. Release skin to stop bleeding and allow minimum 10 days between repeated collections for tissue healing.

Question 5

What are the main complications associated with retro-orbital bleeding?

Accepted Answer

Complications include excessive swelling causing eye protrusion and corneal drying, improper tube placement severing the optic nerve causing blindness, eyeball displacement, orbital bone fracturing, eye globe penetration, and hematoma formation. Despite these risks, when performed by a skilled technician on a fully anesthetized animal, retro-orbital bleeding remains an effective collection method.

Question 6

How does tail snip collection differ from tail vessel nick collection?

Accepted Answer

Tail snip uses a sterile scalpel to cut the tail tip, allowing serial collections by disrupting the original scab. Tail vessel nick is less invasive, making a small cut over the lateral tail vein two-thirds from the rump. Both methods may contain tissue product contamination. Tail snips produce arterial and venous blood, while nicks target venous blood specifically.

Question 7

What is the procedure for intracardiac blood collection and how much blood can be collected?

Accepted Answer

After euthanizing with carbon dioxide, hold the rodent by the scruff with body hanging vertically. Insert the needle bevel-up into the chest at the notch left of the xiphoid, parallel to the spine. Apply slight backpressure; blood flows if needle is in heart. Approximately half the total blood volume can be collected—about 1 mL from mice and 10 mL from rats using anesthesia induction and maintenance protocols.

Blood Withdrawal I - Assessment Quiz