A transfusion in a cat is decided by 2 things read together: the PCV and what the cat is doing. A PCV of 14 percent in a cat that is eating and jumping is a recheck in 24 hours. A PCV of 19 percent in a cat breathing 50 times a minute with a 3-second gum refill is a transfusion tonight. Most clinics transfuse below 15 percent, transfuse at 15 to 20 percent only when signs are present, and almost never above 20 percent unless surgery with heavy expected loss is planned.
The two PCV lines
Below 15 percent, the decision is usually yes: oxygen delivery is roughly 30 percent below normal and the marrow needs 3 to 5 days to respond, which is longer than the cat has. From 15 to 20 percent, the trigger is a sign, not the number: breathing over 40 per minute at rest, heart rate over 220, gum refill over 2 seconds, lactate over 2.5 mmol/L, no food for 24 hours, or a cat that cannot walk 3 steps without sitting. Above 20 percent, transfuse only for planned surgery or active bleeding. As a rough conversion, 1 g/dL of hemoglobin is about 3 PCV points.
Speed of loss matters as much as volume. A cat that dropped from 30 to 18 percent in 6 hours has had no time to expand plasma volume, so it looks worse at 18 than a cat with immune-mediated anemia that has sat at 16 percent for 3 weeks. If you are not transfusing, recheck the PCV at 6 and 12 hours; a fall of 3 points in 6 hours means the bleeding is still going.
Type in 5 minutes
Cats carry type A, type B or, rarely, type AB. Type A covers more than 90 percent of domestic shorthairs in the US. Type B is uncommon overall but reaches 30 to 40 percent in British Shorthairs and Devon Rex, so breed is a hint and never a substitute for a test. A card agglutination test takes 1 to 5 minutes with 1 drop of cells and 1 drop of reagent, and a tube method backs it up in 15 to 30 minutes.
The reason for the 5-minute test is the size of the mistake. A type B cat given even 1 mL of type A blood can hemolyze inside 1 to 5 minutes, with a temperature spike, tremors and red-brown urine, and that reaction kills. The reverse, type A given type B, is mild and the cells simply survive 1 to 2 days instead of 30. The same mismatch explains neonatal isoerythrolysis, where kittens of a type A tom and a type B queen fade at 1 to 3 days on the first nursing.
Crossmatch: 15 to 30 minutes, worth it after 4 days
For a first transfusion, typing alone is accepted in most practices. For a second transfusion more than 4 days after the first, a crossmatch is standard, because antibodies appear within 4 to 7 days of exposure. A major crossmatch pairs recipient serum with donor cells, incubates at 37 C for 15 to 30 minutes, and is read for agglutination or hemolysis; a minor crossmatch reverses the pairing and takes the same time. When the PCV is 10 percent and the cat is collapsing, type and start while the crossmatch runs.
Rate: 10 to 15 mL/kg over 3 to 4 hours
One mL per kg of whole blood raises PCV about 1 point. A 4 kg cat at 12 percent, with a target of 20, needs about 8 x 4 = 32 mL, and a single dose is capped at 10 to 15 mL/kg, which is 40 to 60 mL here. The first 15 minutes run at 0.5 to 1 mL/kg — 2 to 4 mL — so a reaction shows up while the volume is still small. The rest goes over 3 to 4 hours, about 10 mL per hour for that cat, through an 18 to 20 micron filter on a fresh line. No drug goes into the same line, and no calcium-containing fluid meets citrated blood, because citrate binds the calcium.
Donors are 4 to 6 kg, indoor, PCV above 35 percent, negative for FeLV and FIV, and vaccinated; a draw of 10 to 15 mL/kg every 3 to 4 weeks is the usual limit. A unit is used within 4 hours of leaving the fridge.
Monitoring: the first 15 minutes carry the risk
| Minute | Temp limit | HR limit | Action if exceeded |
|---|---|---|---|
| 0 | 39.5 C | 240 /min | Delay 30 min, repeat PCV |
| 5 | +0.5 C | +20 /min | Halve the rate |
| 15 | +1.0 C | +20 /min | Stop, keep line with saline |
| 30 | +1.0 C | +20 /min | Stop, oxygen 40 % |
| 60 | +1.0 C | +20 /min | Stop, recheck PCV at 60 min |
| 180 | +1.0 C | +20 /min | Stop, save the unit |
Reaction signs to write down: temperature rise of 1.0 C or more, heart rate up 20 beats, hives 0.5 to 2 cm, vomiting, tremors, and red-brown urine, the earliest sign of a hemolytic mismatch, which is why urine colour is checked at 15 and 180 minutes. Stop the line, keep the catheter flushed with saline, and keep the bag for retyping and culture. Most reactions appear inside the first 15 minutes, which is why that window runs slow.
When blood is not the answer
Iron-deficiency anemia at 18 to 22 percent with small pale cells needs iron, not a transfusion, and the marrow answers in 2 to 3 weeks. Anemia of chronic kidney disease is handled with darbepoetin and a target PCV of 25 to 30 percent, not with repeated units. Immune-mediated hemolysis at 20 percent with a stable cat is treated with steroids first, and transfusing too early can shorten the survival of the cells you give. A cat with a PCV of 30 percent before elective surgery has no transfusion indication at all — the pre-op panel described in anesthesia for senior cats is the place that number comes from.
Before the next visit
- Ask for the PCV and total protein from today, not just a description, so tomorrow's number has a baseline.
- If a transfusion is planned, ask for the type card result in writing and the crossmatch time.
- Book the 24-hour PCV recheck; a rise of 4 to 6 points that holds at 24 hours is a success.
- Keep the cat indoors and quiet for 48 hours, and watch the urine colour for 24 hours.
- Note the cat's age in human terms with the cat age calculator; an older cat with a PCV of 19 needs a search for the cause, not only blood.
Terms mentioned in this article
Frequently asked
My cat's PCV is 18 percent. Does it need a transfusion?
Not from the number alone. Between 15 and 20 percent the trigger is a clinical sign: resting breathing over 40 per minute, heart rate over 220, gum refill over 2 seconds, lactate over 2.5 mmol/L, or a cat that cannot walk 3 steps without sitting. A bright cat eating normally at 18 percent usually gets a recheck at 6 and 12 hours instead, and a fall of 3 points in 6 hours changes the plan.
Why test blood type if most cats are type A?
Because the mismatch is fatal and the test takes 1 to 5 minutes. Type B is rare overall but reaches 30 to 40 percent in British Shorthairs and Devon Rex, and a type B cat given 1 mL of type A blood can hemolyze within 1 to 5 minutes. Breed is a hint, never a substitute, so every cat gets a card test before the first unit is hung.
How fast should a cat transfusion run?
The first 15 minutes run at 0.5 to 1 mL/kg, which is 2 to 4 mL for a 4 kg cat, so a reaction shows while the volume is small. The remainder goes at a total of 10 to 15 mL/kg over 3 to 4 hours, about 10 mL per hour for that cat, through an 18 to 20 micron filter. No drugs go in the same line, and no calcium-containing fluid meets citrated blood.