Anticoagulant rodenticide screen in cats and dogs
Anticoagulant rodenticides are rat and mouse poisons that stop the blood from clotting properly. The screen looks for the poison itself in serum, plasma or tissue, while clotting tests show its effect on the blood. Clotting times change only after a delay of days, so both kinds of test are read together with the history of possible exposure.
What it shows
These poisons block vitamin K recycling in the liver. Without it, the liver cannot finish making clotting factors II, VII, IX and X. Factors already in the blood keep working for a while, then run out.
Two different kinds of test answer two different questions:
- Rodenticide screen — a toxicology test that measures the poison itself by chromatography (for example liquid chromatography with mass spectrometry). It is done in a specialised laboratory, not in the clinic. One laboratory panel lists ten compounds, including warfarin, brodifacoum, bromadiolone, diphacinone and chlorophacinone, and its turnaround is about ten business days. Such screens are rarely performed in everyday practice; they confirm exposure and show which compound was involved.
- Clotting tests — PT and APTT show whether the blood is actually clotting more slowly. They do not show the cause: a long PT can have other reasons.
Why PT is not prolonged at once: the affected factors have half-lives of roughly 6–16.5 hours, and the circulating supply is used up 24–64 hours after a toxic amount is eaten. Clotting test results therefore change 2–5 days after ingestion, and bleeding is typically noticed 3–7 days after. Factor VII has the shortest half-life, so in cats and dogs PT lengthens first and APTT shortly after.
Higher than reference — what it may be a sign of
- Positive (anticoagulant detected) — the animal has been exposed to an anticoagulant rodenticide, directly from bait or by eating a poisoned rodent. The name of the compound matters: compounds differ in how long they act — from days to weeks — and identifying it helps the vet plan how long care continues.
- Positive together with a long PT — the poison is present and is already affecting clotting. By the time bleeding is seen, both PT and APTT are usually prolonged.
- Signs that may go with it — weakness, lethargy, poor appetite, nosebleeds and breathing difficulty; less typical signs such as joint pain or seizures depend on where the bleeding is.
If poisoning is suspected — go to the vet straight away, do not wait for a test result.
Lower than reference
A negative screen means none of the compounds on that laboratory’s list was found in the sample. The panel looks only for the compounds it lists, so the result is read together with the history and the clotting tests. A normal PT soon after a possible exposure does not rule poisoning out either: clotting times change only after the factors already in the blood are used up, which is why vets may recheck PT about 48 hours later.
Look at together with
- PT and APTT — show the effect of the poison on clotting; PT changes first.
- Platelets — normal in many cases, mildly to moderately low after marked blood loss.
- Hematocrit and total protein — anaemia is usually mild to moderate when signs are first noticed, but can be severe.
- Other causes of a long PT — vitamin K shortage from fat malabsorption or blocked bile flow, long antibiotic courses, liver disease, DIC and inherited factor deficiencies. So it is the screen, not PT alone, that confirms a rodenticide.
Units and conversion
The screen has no unit in the app. The result is recorded as text: whether an anticoagulant was detected or not detected, often with the name of the compound. Clotting tests are separate rows with their own units (PT and APTT in seconds).
Reference range
The reference range is on your lab’s form; for this test the expected result in a healthy animal is “not detected”. A positive result confirms exposure. What it means for the animal right now the vet decides together with the clotting tests, blood count and the animal’s condition.
Cats and dogs
Rodenticide-related clotting problems are somewhat less common in cats than in dogs. Cats can be poisoned not only by bait but also indirectly, by eating poisoned rodents. As in dogs, PT lengthens first and APTT shortly after.
In dogs rodenticide-related clotting problems are fairly common. A dog may look well for several days after eating bait: clotting tests change 2–5 days after ingestion and bleeding is typically noticed 3–7 days after. Bleeding can be hidden — into the chest, lungs, abdomen or joints — so signs vary.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Merck Veterinary Manual — Anticoagulant rodenticide poisoning in animals
- eClinPath (Cornell) — Vitamin K: anticoagulant rodenticide toxicosis
- Kansas State Veterinary Diagnostic Laboratory — Rodenticide poisoning in companion animals
- Texas A&M Veterinary Medical Diagnostic Laboratory — Anticoagulant rodenticides (LC/MS)
- Merck Veterinary Manual (Pet Owners) — Rodenticide poisoning
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.