Final answer:
To assess clotting factors in a dog with a bleeding disorder, blue top (citrate) tubes should be used, as they preserve clotting factors needed for laboratory analysis without initiating clots, unlike tubes with other additives.
Step-by-step explanation:
To assess clotting factors in a dog with a bleeding disorder, you would look at plasma samples from blue top (citrate) tubes. These tubes contain citrate, which acts as an anticoagulant by binding calcium, thereby preserving the clotting factors for laboratory analysis. The blue top tubes are specifically used for coagulation assays because they allow for the assessment of the coagulation system without the initiation of clotting. On the other hand, the green top (heparin) tubes contain heparin, which inhibits thrombin and prevents clotting, but is not the preferred choice for coagulation studies. Red top (serum) tubes would give you serum, not plasma, since the clotting factors would have been consumed during the formation of the clot. Purple top (EDTA) tubes prevent clotting by chelating calcium but are generally used for complete blood counts (CBC) and not for coagulation studies. Therefore, for accurate measurement of clotting factors such as fibrinogen and platelet function, blue top tubes are the appropriate choice.