A coagulation panel before surgery answers 1 question: will this cat stop bleeding on the table? The printout carries 4 numbers, PT, aPTT, platelet count and fibrinogen, and they are read at 3 time points. Abnormal results fall into 2 patterns, not 20.
Healthy cats rarely need more than 1 baseline panel. The test earns its cost when there is a bleeding history, liver disease, or a planned biopsy of a well-vascularized organ.
The 4 lines that matter
PT tests the extrinsic and common pathway (factors VII, X, V, II, fibrinogen) and lands near 6.5 to 12.0 s on most feline analyzers. aPTT tests the intrinsic and common pathway (XII, XI, IX, VIII) and runs 10 to 18 s. Platelets sit at 200 to 600 x10⁹/L, fibrinogen at 100 to 400 mg/dL. Treat those as typical, not universal: the same plasma can read 8 s at 1 lab and 10 s at another.
1 range is not the range
Reagent, calcium source and analyzer optics shift PT by 1 to 3 s between laboratories. A printed range of 6.5 to 12.0 s at hospital A can be 7.5 to 13.5 s at hospital B for the same cat and the same plasma. Read the range printed on the report in front of you, not a textbook number, and not a range from a previous visit at a different clinic.
Pre-analytic error moves these numbers more than disease does. An underfilled citrate tube, below 90 percent of the draw volume, lengthens PT and aPTT by 1 to 2 s. Plasma left on the cells for 5 hours at room temperature loses factor V. A hemolyzed sample reads long. If 1 value is mildly off in a well cat, the first move is a clean redraw from a quiet vein.
Time point 1: 5 to 7 days before
This is the baseline, drawn once at the pre-anesthetic visit. It is the only sample that describes the cat before fasting, catheterization and anesthesia touch it. PT plus aPTT together cost 35 to 90 USD. If it comes back abnormal, the 5 to 7 days buy room for a repeat, a mixing study or a factor assay instead of a cancelled procedure.
Draw 1.0 to 1.8 mL into a 3.2 percent citrate tube, fill to the line, invert 3 to 4 times, and spin within 1 hour. No fasting is needed. Ask the lab to freeze a spare aliquot if the cat has bled before; that aliquot saves a second visit.
Time point 2: 24 to 48 hours before
Repeat only if the baseline was abnormal or the cat changed: a new drug in the last 7 days, vomiting for more than 24 hours, fever above 39.5 °C, or a liver enzyme that tripled. This draw catches interval change and it is the last window in which a surgical plan can still move. A stable cat with a normal baseline skips it.
Time point 3: 12 to 24 hours after
Not routine after a dental. Indicated after a liver or kidney biopsy, a splenectomy, more than 2 extractions, or any oozing at the incision. Check PCV, platelet count and the wound itself. A PCV drop of 5 points in 24 hours, a swelling that grows 2 cm, or fresh blood on the bandage at 6 hours turns the third time point into a same-day recheck.
Pattern 1: prolonged clotting times
Isolated PT prolongation points at factor VII, liver synthesis or vitamin K antagonism; rodenticide exposure is the classic, and indoor cats in houses with bait stations are exposed more often than owners think. Isolated aPTT prolongation points at factors VIII, IX, XI or XII, at heparin left in a catheter line, or at a traumatic draw. Both prolonged points below the common pathway: severe liver failure, disseminated intravascular coagulation, or rodenticide at day 3 to 5 of exposure.
A mixing study separates the 2: correct with normal plasma and a missing factor is the problem; stay long after mixing and an inhibitor or heparin is present. That interpretation belongs to the laboratory and the clinician, not to a number read off a page.
Pattern 2: normal times, abnormal cells
Platelets of 100 to 200 x10⁹/L are usually watched and rechecked in 3 to 5 days. A count of 50 to 100 postpones elective surgery, and under 50 postpones any extraction or biopsy. Fibrinogen under 100 mg/dL suggests consumption rather than poor synthesis; above 400 mg/dL it is inflammation, not a bleeding risk. A buccal mucosal bleeding time over 4 minutes flags a platelet function problem that a count cannot see.
The numbers, and what each one gates
| Measurement | Typical feline range | Action threshold | Result time |
|---|---|---|---|
| PT | 6.5 to 12.0 s | over 15 s defers surgery | 1 to 2 hours |
| aPTT | 10 to 18 s | over 25 s defers surgery | 1 to 2 hours |
| Platelets | 200 to 600 x10⁹/L | under 50 cancels extraction | 30 minutes |
| Fibrinogen | 100 to 400 mg/dL | under 100 flags DIC | 2 to 4 hours |
| Buccal bleeding time | 1 to 4 minutes | over 4 minutes flags function | 15 minutes |
| PCV after surgery | 30 to 45 percent | drop of 5 points rechecks | 5 minutes |
Six rows, and only 2 of them are clotting times in the strict sense. The other 4 explain most surprises: a cat with a normal PT and aPTT can still bleed from 40 x10⁹/L platelets or from platelets that do not stick.
When this stops being a lab question
Bleeding from 2 or more sites, a nosebleed that lasts 10 minutes, blood in the urine, a bruise wider than 3 cm appearing without trauma, or pale gums with a PCV under 20 percent. Those are emergency signs, and the panel is drawn on the way to treatment, not before it. A cat that has eaten rodenticide needs care within hours, not a scheduled recheck in 7 days.
5 steps before the appointment
- Ask for PT, aPTT, platelets and fibrinogen by name, and ask for the printed reference range on the same page.
- Book the baseline 5 to 7 days out, not 3 weeks, so an abnormal result still leaves time for a repeat.
- List every drug from the last 30 days, including NSAIDs, steroids and any supplement that contains fish oil or vitamin E.
- Write down any bleeding episode: how long, from where, and how it stopped. That history outranks 1 borderline value.
- If the cat is scheduled for a biopsy, ask whether the third time point is planned at 12 to 24 hours.
For how these clotting factors behave in the whole picture, the anatomy sits in the coagulation system guide, and if you are still choosing a cat, breed traits and inherited risks are covered in the breed quiz.
Terms mentioned in this article
Frequently asked
Does a normal PT and aPTT mean the cat cannot bleed?
No. The 2 tests cover the clotting factors, not platelet function or vessel wall. A cat with 40 x10⁹/L platelets, or with platelets that do not aggregate, can bleed with a perfectly normal PT and aPTT. Ask for a platelet count and a buccal mucosal bleeding time when there is a bleeding history.
Why does my cat need a repeat test 24 to 48 hours before surgery?
Because the first panel may be 5 to 7 days old and a lot can change: a new drug, a fever, vomiting, or a liver value that tripled. The repeat is only needed when the baseline was abnormal or the cat changed. A stable cat with a normal baseline skips that draw entirely.
Can I compare this result with one from another clinic?
Only loosely. Reagents and analyzers differ, so PT can move 1 to 3 s and aPTT 2 to 4 s between laboratories for the same plasma. Compare each result with the range printed on its own report, and bring the old report with you so the clinician can see both ranges side by side.