Microtainers are preferred for specimens of small volume. It is important to pay careful attention to handling and filling of the specimen tubes.

Tubes containing anticoagulant also have a small plastic bead or donut to aid in proper sample mixing. These must be at least ½ full to achieve a usable anticoagulant: blood ratio. Mix well by inversion (at least 5 times) immediately after collection to prevent clotting.

Tubes without anticoagulant are filled with the requisite volume and left for at least ½ hour at room temperature or until clotting is achieved.

If required, centrifuge the specimen and transfer plasma or serum to a plain red-top microtainer (unless a separator tube is used which eliminates the need for transfer).

Green Top Tube, Plain (without separator gel), contains heparin, and can be used for tests requiring heparinized plasma or whole blood.

Green Top Separator Tube also contains heparin plus an inert separator gel, and is the preferred specimen for tests requiring heparinized plasma.

Lavender Top Tube contains EDTA and is generally used as the specimen of choice for avian and small mammal CBC and other studies of blood cells. Certain tests also recommend EDTA plasma (see table).

Red Top Tube, Plain (without additives) is used for any test requiring serum. After the specimen has clotted, the serum should be separated from the blood cells promptly to obtain optimum results.

Brown Top Separator Tube contains an inert separator gel which eliminates the necessity of transferring the serum to another tube after centrifugation. These tubes should not be used for measuring drug levels.

Microhematocrit Tubes (plain or heparinized), 2 or more, also can be used for some tests (see table).