A transfusion reaction can start within 3 minutes of the first milliliter, and by minute 15 the cat has usually shown you everything you need. Cats hide the classic signs: no dramatic rash, no obvious swelling, just a temperature climbing from 38.6 to 39.7 °C, a heart rate going from 160 to 195, and a cat that stops grooming and stares at the wall. Monitoring has to be numeric, written down, and compared against a baseline taken before the line went in. When a number crosses a threshold, the line stops. It does not slow down.
Why minute 15 decides more than hour 3
Most severe reactions are early. Acute hemolysis from a mismatched unit, bacterial contamination in a bag stored past 35 days, and anaphylaxis to donor plasma protein all declare themselves while the volume given is still small. A 4 kg cat at 10 mL/kg receives about 40 mL of packed red cells over 3 to 4 hours, close to 0.2 mL per minute, which is the replacement volume for a measured blood loss of roughly 10 mL/kg. At minute 15 only 3 mL has gone in. Stopping there wastes 3 mL of product. Stopping at minute 90 wastes 18 mL and adds 75 minutes of circulating antigen. There is no prize for finishing the bag.
Five numbers before the first drop
Record these before the line is connected: rectal temperature to one decimal, heart rate, respiratory rate, body weight, and packed cell volume. Temperature is the number people skip and the one that catches grade 2 reactions first. Use a rectal thermometer, not an ear thermometer: ear readings drift by 0.5 °C or more in cats and will hide the 1 °C rise you are hunting. A calm cat runs 140 to 220 beats per minute, so write the actual figure down. A cat that was 160 and is now 195 has risen 22 %, past the 20 % line before any swelling appears.
The four grades and the numbers behind them
| Grade | What you see | Temp rise | Heart rate rise | Action |
|---|---|---|---|---|
| 1 | Mild hives, restlessness, one vomit | under 0.5 °C | under 10 % | Halve the rate, recheck at 5 minutes |
| 2 | Facial swelling, salivation, 2 vomits | 0.5 to 1.0 °C | 10 to 20 % | Pause 5 minutes, call the vet, restart only if resolved |
| 3 | Dyspnea, weak pulse, red-brown urine | over 1.0 °C | over 20 % | Stop for good, keep the catheter, treat |
| 4 | Collapse, gasping, arrest | over 1.5 °C | over 30 % | Stop, resuscitate, no restart |
Grade 1 is common and often settles in 5 to 10 minutes at half rate. Grade 2 needs a decision inside 10 minutes, because it can become full anaphylaxis before the next reading. Grade 3 means that unit never goes back in, even if the cat looks normal again at minute 20, because the next 5 mL will reproduce the reaction faster and harder.
Grade 3 signals that arrive before the label
Watch four things between minute 0 and minute 30: red-brown urine in the litter box or the line, a resting respiratory rate above 40 per minute, systolic pressure under 90 mmHg where a Doppler is available, and a cat that will not lift its head. Any 2 of those 4, with or without a temperature change, is handled as grade 3. One vomit is grade 1 territory. Three vomits in 10 minutes is not.
On-site handling while the line is still running
Clamp first, then call. Do not pull the catheter: you may need it for fluids and a bleeding site on a hypotensive cat is one more problem. Flush with saline at the volume already prescribed rather than disconnecting. Leave the bag attached and labelled, because the unit number, collection time and donor ID are what the clinic needs to file a report. If the cat is dyspneic, keep it sternal, never on its back, and hold the room at 25 to 28 °C. Recheck temperature and heart rate at minute 2 and minute 5 after clamping, since some reactions peak 10 minutes after the antigen load stops rising.
Vet thresholds in minutes
0 minutes: collapse, open-mouth breathing or a seizure. Carry the cat out, leave the bag. 5 minutes: grade 2 signs that have not improved after a 5-minute pause. 15 minutes: any 1 °C rise or any 20 % heart rate rise, even in a cat that looks comfortable. 30 minutes: hives, a single vomit, or a 0.5 °C rise that holds on a second reading 10 minutes later. 60 minutes: any cat that reacted at all is seen the same day. Delayed hemolysis can surface at 3 to 7 days with jaundice, a falling PCV and dark urine, and it is the reason a reaction gets written into the record.
Carrying and warming on the road
Double-bag the unit and its label, and keep it off the seat where it can roll. Bring the last 3 temperature and heart rate readings on paper or a phone note; a clinic triages a trend faster than a single number. Warm the carrier to 28 to 30 °C with a covered pack along one wall, never underneath the cat, and test the pack against your wrist every 15 minutes. A cat in shock loses heat quickly, and a 1 °C fall in core temperature worsens clotting and slows drug clearance. No food, no water, and no antihistamine from the home cabinet: it flattens the hives without touching the reaction and blunts the clinic's read.
After the reaction: 72 hours of watching
Ask for the unit number and the grade in writing. Expect a PCV and bilirubin check at 24 hours, and a second at 72 hours if the first was off. Watch urine color for 3 days; cola-colored urine means a call, not a wait. Ask for a cross-match before any future transfusion and have the note put on the file, because a second exposure to the same antigen moves faster than the first and needs less volume to do it.
- Write a baseline temperature, heart rate and respiratory rate before the line goes in.
- Stay at the table for the first 15 minutes with a thermometer and a timer.
- Stop at 1 °C or 20 %, not at the end of the bag.
- Keep the bag, the label and the trend, and hand all 3 to the vet.
- Recheck PCV at 24 and 72 hours and record the grade in the chart.
Terms mentioned in this article
Frequently asked
What is usually the first sign of a transfusion reaction in a cat?
A rise in rectal temperature, often 0.5 to 1 C above the baseline taken before the line went in. Hives and facial swelling are less reliable in cats, so temperature and heart rate are the two numbers worth writing down at minute 0, 15 and 30.
Should I stop the transfusion on my own?
Clamp the line at 1 C of temperature rise or a 20 percent jump in heart rate, then call the clinic before restarting anything. Stopping early costs a few milliliters of product; pushing through a grade 3 reaction costs the cat its life.
How long after a reaction should the cat be watched?
At least 72 hours. Delayed hemolysis can appear 3 to 7 days later as jaundice, dark urine and a falling packed cell volume, which is why the unit number and the reaction grade belong in the written record.