With the animal standing quietly, make a cut about 1.5 cm long on the inside surface of the lower lip. Use a fresh scalpel blade wrapped with adhesive tape to expose about 3 mm of the blade tip. Hold the blade between thumb and forefinger at the level of the tape to control the depth of incision. Incise with steady pressure. Let bleed freely and time until bleeding stops. Normal values are up to 8 or 9 minutes. Prolonged bleeding or rebleeding once it has stopped is abnormal. Bleeding times measured with this template-type technique are primarily sensitive to defects of platelet function (quantitative and/or qualitative).

The basic coagulation profile evaluates intrinsic (APTT) and extrinsic (PT) coagulation activity and the presence of DIC (fibrinogen and FDP tests). It will not diagnose cases of vWD. Coagulation laboratories have historically used the thrombin time test to screen for the presence of fibrinogen-fibrin degradation products. However, the thrombin reagents used today are insensitive to the presence of FDP based on a thorough evaluation recently performed at Antech. These reagents are useful, however, for determining fibrinogen concentration based on the thrombin clottability technique. Consequently, Antech will no longer offer the thrombin time test but will replace it with a fibrinogen activity assay and FDP measurements (D-dimer test).

Special coagulation factor assays can be performed on a send-out basis, if the basic coagulation profile results and clinical or family history so warrant. Please contact the laboratory for specific instructions to prepare and submit these samples, as they need to be sent frozen with dry ice. The most common problems encountered with samples submitted for coagulation evaluation are as follows:

• Clotted or hemolyzed specimens. Clots of any size and moderate to significant hemolysis will invalidate coagulation and vWD tests.
  
• Wrong anticoagulant – EDTA (LTT) or heparin (GTT) instead of citrate (BTT).
  
• No anticoagulant – clotted serum tube or FDP tube used instead of BTT.
  
• Improperly filled Vacutainer tube. Sample tubes filled to only half or less are overdiluted with citrate and will likely produce invalid (prolonged) results.
  
• Incomplete or missing patient descriptors (e.g., species, age, sex, breed, neutered or intact).
  
• Specimens held too long prior to pick up or mailed- in with more than a 24-hour receiving delay can produce erroneous coagulation results. In such cases we prefer that BTT samples be spun down soon after collection, and the plasma removed and placed into an empty plastic or silicone-coated glass tube prior to submission. A LTT sample is still required for the CBC/platelet count portion of this profile.

The most important points in obtaining valid specimens for coagulation assays are a clean venipuncture with rapid blood flow into the collection syringe or Vacutainer tube, and the correct volume of blood to fill the tube.

A recent clinical case illustrates the value of coagulation testing. A one-year-old spayed female cat was admitted to an emergency clinic for evaluation of severe anemia (PCV 7%). She was FIA positive for hemobartonellosis. A routine coagulation profile revealed: PT 14.0 sec (normal range 9-12 sec).

APTT > 60 sec (18-22 sec)

Thrombin time 5.5 sec (5-9 sec)

Platelet count 33,000/pl (200-500,000/pl)

Fibrinogen < 100 mg/dl (100-400 mg/dl)

Three weeks later after treatment for the hemobartonella, followup testing showed PCV had risen to 17%, 16 nucleated RBC/100 WBC, FIA was negative but the coagulation profile remained abnormal:

PT 10.1 sec. APTT > 60 sec.

Thrombin time 6.6 sec.

Platelet count 130,000/pl

Fibrinogen 319 mg/dl

Because there was no overt bleeding tendency observed in this patient and it was a cat with persistently long APTT, the presumptive diagnosis of the coagulopathy was Hageman trait (factor XII deficiency). This condition is relatively common in cats, and is usually an incidental finding not associated with excessive bleeding unless some other hemostatic defect coexists (e.g., thrombocytopenia). Citrated plasma was submitted in dry ice to the Comparative Coagulation Section at Cornell University’s Diagnostic Laboratory and revealed a factor XII level of 1.5% (normal range 60-150%). This confirmed the diagnosis as Hageman trait.