Recent introduction of Antech's enhanced Preanesthetic Profile [SA050; PreOp/CBC] has raised several issues with respect to obtaining proper anticoagulated blood samples for the coagulation PT and PTT portion of this profile.

Discussion of some commonly asked questions about the diagnosis of bleeding diseases is also found in Antech News, February 2006.

The following information is intended to clarify this situation:

Collection of blood samples into a dry syringe can result in activation of the initial coagulation cascade with prolongation of the results, despite clean venipuncture and good blood flow. This problem is most often encountered when the animal being bled is very small, has slow blood flow, or is difficult to restrain for the collection.

A second common problem with coagulation samples is overcitration, which also prolongs results, because the BTT is inadequately filled to achieve the correct 1 in 10 final citrate: blood ratio. The BTT should ideally be completely full, but must be at least 2/3 rds full to avoid artifactual coagulation results due to overcitration. NOTE: Do not use expired BTT.

The preferred way to collect blood for coagulation assays is to preload the syringe with the appropriate amount of citrate anticoagulant. For example, if using the small 1.8 mL BTT, please draw all the citrate into the syringe and then collect enough blood to achieve a total of at least 1.5 - 1.8 mL of anticoagulated sample. Mix immediately and place the anticoagulated blood back into the original BTT. If using a larger BTT, one example would be to preload the syringe with 0.3 mL of citrate and draw up to at least 2 mLs (ideally 2.7 mLs) with blood. The advantage of this technique is that the blood is anticoagulated as soon as it enters the syringe. If a clean venipuncture is not obtained, the needle should be replaced with another, and a second venipuncture made (the same syringe can be used). Immediately after collecting the required amount of blood, the syringe should be gently mixed. If incomplete collection occurs, the needle can be withdrawn and syringe mixed; and then another needle can be attached to complete the collection.

If proper blood collection is obtained but the results of the PT and/or PTT are abnormal, the risk of the patient to bleed excessively during or following an operative procedure can be further assessed by performing the bleeding time. The toenail or cuticle bleeding time is preferred because it evaluates both primary and secondary hemostasis best simulates surgical severing of a blood vessel. The mucosal bleeding time, on the other hand, primarily assesses the platelet function of primary hemostasis, and does not evaluate secondary hemostasis and stabilization of the initial hemostatic plug.

With the animal in lateral recumbancy, either awake or anesthetized (sedatives and anesthetic agents will not significantly affect bleeding times), use a sharp, guillotine-type toe nail clipper to make a clean transection of the nail just into the quick (becomes reproducible with practice). Let the nail bleed freely undisturbed and time until bleeding stops.

Normal TNBTs are up to 5 1/2 mins in dogs and 3 1/2 mins in cats. A prolonged bleeding time or rebleeding after initial bleeding has stopped is considered abnormal.

Bleeding times measured by this transection technique are sensitive to defects in blood vessel contraction (vascultitis), platelet number and function, and coagulation. This test can be useful for:

• pre-surgical assessment of bleeding potential
  
• evaluation of response to therapy in bleeding animals
  
• determination of degree of bleeding risk (e.g., slight prolongation by1-3 mins may be manageable conservatively without transfusion; moderate to severe prolongation by 3 or more mins usually requires treatment before surgery or to alleviate clinical signs; bleeding times of over 10 mins are significantly prolonged and require treatment).