Veterinary Coagulation Panel Interpretation Reference
Interpret PT, aPTT, platelet count, BMBT, fibrinogen, and D-dimer patterns to narrow the differential for a bleeding or clotting disorder in dogs and cats.
Individual tests
| Test | What it means |
|---|---|
| PT (Prothrombin Time) | Tests the extrinsic + common pathway (factors VII, X, V, II/prothrombin, fibrinogen). Factor VII has the shortest half-life of the coagulation factors, so PT is typically the FIRST value to prolong in early anticoagulant rodenticide toxicity and in early liver synthetic failure. |
| aPTT (activated Partial Thromboplastin Time) | Tests the intrinsic + common pathway (factors XII, XI, IX, VIII, X, V, II, fibrinogen). Prolonged in hemophilia A (factor VIII deficiency) and hemophilia B (factor IX deficiency), heparin therapy, DIC, and more advanced liver disease or rodenticide toxicity. |
| Platelet count | Thrombocytopenia causes include immune-mediated thrombocytopenia (ITP), DIC, bone marrow disease, and tick-borne infections (e.g. Ehrlichia). Spontaneous bleeding risk (petechiae, ecchymoses) becomes a concern below roughly 30,000-50,000/µL; count below ~10,000-20,000/µL carries risk of spontaneous serious hemorrhage. |
| Buccal Mucosal Bleeding Time (BMBT) | Screens PRIMARY hemostasis (platelet function and von Willebrand factor activity) - useful when platelet COUNT is normal but a bleeding tendency is still suspected. Normal is approximately 1.7-4.2 minutes in dogs. |
| Fibrinogen | Decreased with consumption (DIC) or severe liver failure; increased as a nonspecific acute-phase reactant with inflammation. |
| D-dimer / Fibrin Degradation Products (FDPs) | Elevated with DIC and thromboembolic disease. |
Pattern interpretation
| Pattern | Likely cause(s) |
|---|---|
| Prolonged PT, normal aPTT | Early anticoagulant rodenticide toxicity, mild/early liver synthetic dysfunction, isolated factor VII deficiency (rare). |
| Prolonged PT AND aPTT | More advanced anticoagulant rodenticide toxicity, DIC, severe liver failure, vitamin K deficiency/malabsorption. |
| Prolonged aPTT, normal PT | Hemophilia A or B, heparin therapy, factor XII deficiency (usually clinically silent). |
| Normal PT/aPTT with active bleeding or petechiae | Check platelet count and BMBT - suspect thrombocytopenia or a primary hemostatic disorder (platelet dysfunction, von Willebrand disease) rather than a coagulation factor problem. |
| Low platelets + prolonged PT/aPTT + elevated D-dimer | Classic DIC picture (consumption of both platelets and clotting factors). |
These are general interpretive patterns, not a substitute for clinical judgment - always correlate with history (rodenticide exposure, hepatic disease, breed-associated hemophilia), physical exam findings, and other bloodwork.
Frequently asked questions
Why does PT prolong before aPTT in early rodenticide toxicity?
Factor VII, part of the extrinsic pathway that PT measures, has the shortest half-life of the vitamin K-dependent factors. It depletes and prolongs PT first, before the intrinsic-pathway factors measured by aPTT are affected.
What does a normal PT/aPTT with active bleeding mean?
It points away from a coagulation factor problem and toward a primary hemostatic issue - check platelet count, and if that's normal too, run a BMBT to screen for platelet function defects or von Willebrand disease.
What is the classic DIC coagulation picture?
Thrombocytopenia, prolonged PT and aPTT, low fibrinogen from consumption, and elevated D-dimer/FDPs - reflecting simultaneous clot formation and factor/platelet consumption.
What is BMBT used for?
Screening primary hemostasis - platelet function and von Willebrand factor - specifically when the platelet count itself is normal but a bleeding tendency is suspected, since count alone doesn't assess platelet function.