Collection Tube Order

Following an order of blood draw ensures the integrity of the specimens by avoiding cross-contamination of additives between tubes. For example, even small amounts of EDTA can interfere with several of the chemistry results. EDTA prevents coagulation by chelating calcium, and will also chelate other divalent anions (e.g. magnesium and iron). Cross-contamination of plain tubes for chemistry panels with EDTA will therefore cause false hypocalcemia and hypomagnesemia, and false decreases in iron. Potassium-EDTA will also cause a false hyperkalemia.

The Clinical Laboratory Standards Institute (CLSI) has established a recommended order of draw to prevent such errors.1 These recommendations can be applied for veterinary specimens. The order is the same whether the blood is collected by vacutainers, syringe, or a winged collection set.

  • Blood culture tubes should always be drawn first. The VDL uses the Signal blood culture system where the media in the bottle is specially formulated to encourage growth of aerobic, microaerophilic, and anaerobic organisms. After collection of this specimen, the recommended order is:
EU Colour Code Type of Tube US Colour Code
Sodium citrate tubes
Serum tubes (with or without clot activator or gel)
Heparin tubes
EDTA tubes
Sodium fluoride/potassium oxalate with antiglycolytic inhibitor

Collection Tube Type

The submitting veterinarian should be aware which type of tube is the appropriate one for a designated test. Briefly, complete blood counts (CBCs) should be evaluated on samples collected into EDTA tubes and alternatively heparin. Some disadvantages of heparin are that heparin will increase platelet clumping, which will falsely decrease the platelet count. Additionally, after exposure to heparin, cells will not stain normally (they will stain with a pinkish hue that makes difficult the evaluation of cell morphology). In some species of birds and reptiles however, the preferred anticoagulant is heparin, as blood will hemolyze after exposure to EDTA. Either serum or plasma from a sample collected into a plain (without anticoagulant) or heparin tube, respectively, are adequate specimens for a chemistry panel. For the reasons previously mentioned, chemistry panels should not be done on plasma from blood collected into EDTA. Sodium citrate tubes are generally used for hemostasis testing.

Feel free to contact the VDL at 3442-4849 if you have questions about what tube to use!