Buccal mucosal bleeding time (BMBT) in cats and dogs

What it shows

When a small vessel is cut, platelets stick to the wound with the help of von Willebrand factor and form the first plug — primary hemostasis. BMBT watches exactly this step. The upper lip is folded up and held with a gauze tie; a spring-loaded device makes one or two standard cuts, a few millimetres long and about 1 mm deep, above the premolars. Blood is blotted with filter paper held close to the cut but not touching it, and the stopwatch stops when the paper no longer picks up blood.

The test reflects platelet number and function, the amount and function of von Willebrand factor and, rarely, vessel-wall defects. When done properly it stays normal in disorders of clotting factors, such as hemophilia or anticoagulant rodenticide poisoning. If the dog is sedated or anaesthetised, this can mildly prolong the time.

A different test, the cuticle (toenail) bleeding time, also reacts to clotting-factor deficiencies; it is not the same as BMBT.

Higher than reference — what it may be a sign of

• Low platelet count — in dogs the time is prolonged with counts below 90,000/µL, so the test is meaningful only when the platelet count is adequate.
• von Willebrand disease — the most common cause of a prolonged BMBT with a normal platelet count. Usually it takes a moderate to severe deficiency, typically below 20% vWF antigen; in the most severe form (type 3) bleeding can last over 10 minutes or not stop on its own. Type 2 can prolong it at higher levels.
• Platelet function defects — inherited (for example Chédiak–Higashi syndrome in cats) or acquired (uremia, medicines that act on platelets). The test is insensitive to these: medicines that act on platelets may prolong it only mildly.
• Technique — pressing the device too hard, a tight gauze tie or paper touching the cut can all lengthen the time.

Lower than reference

A short bleeding time has no meaning — only prolongation is interpreted. A normal BMBT does not rule out a bleeding disorder: mild von Willebrand disease often gives a normal or inconsistent result, and the lip test does not reliably pick up clotting-factor deficiencies.

Look at together with

• Platelet count — checked first; a low count by itself prolongs BMBT.
• von Willebrand factor antigen — the lab test that actually measures the factor.
• PT, aPTT and ACT — clotting-factor tests that BMBT does not replace.
• Urea — uremia can disturb platelet function.

Units and conversion

BMBT is recorded in minutes (min); some references give seconds. One minute is 60 seconds, so 2 minutes equals 120 seconds. The app stores the result in minutes.

Reference range

The reference range is on your lab’s form — for BMBT that is the record of the clinic that did the test, because the result depends on the device, the person doing it and whether the animal was sedated. In dogs a normal BMBT is generally under 4 minutes; in one study of unsedated mixed-breed dogs it reached up to 3.2 minutes. Greyhounds have their own published interval (53–235 seconds with one device).

Repeatability is poor: in the same dog or cat the same person’s results varied by as much as 80–87 seconds. That is why the test is not used to predict bleeding during surgery, and a prolonged result is checked with more specific tests; a platelet function analyser is preferred where it is available.

Cats and dogs

Sources

1. eClinPath (Cornell University College of Veterinary Medicine). Hemostasis — Buccal mucosal bleeding time (BMBT).
2. Cornell University Animal Health Diagnostic Center, Comparative Coagulation Laboratory. Bleeding Time Tests (clinical topic).
3. McQuinn E. Overview of Hemostatic Disorders in Animals. Merck Veterinary Manual, full review February 2025.
4. McQuinn E. Platelet Disorders in Animals (von Willebrand disease). Merck Veterinary Manual, full review February 2025.