What Staff Should Know About Blood Typing And Cross-matching

by Veterinary Practice News Editors | April 17, 2009 4:06 pm

Canine Blood Types
DEA System (Dog Erythrocyte Antigen)

Dogs currently have 13 known erythrocyte antigens, nine of which are listed below. Dogs do not have naturally occurring antibodies to DEA 1.1, and 1.2, the most antigenic subgroup, but studies do show they do have naturally occurring antibodies to 3, 5, and 7.

Because of the lack of antibodies to DEA 1.1 or 1.2 it is often said that the “first transfusion is safe no matter the type,” but this practice should be abandoned as typing materials are inexpensive and readily available, and the patient may require additional transfusion later in his lifetime.

Antigen Incidence of positive in Population   Reaction Seen w/ Mismatch
DEA 1.1 33%-45%  Acute Hemolytic Rxn
DEA 1.2 7%-20% Acute Hemolytic Rxn
DEA 1.3 Unknown   Delayed Hemolytic Rxn
DEA 3 5%-10%   Delayed Rxn, RBC removal
DEA 4 87%-98% None
DEA 5 12%-22% Delayed Rxn, RBC removal
DEA 6 99% Unknown
DEA 7 8%-45% Delayed Rxn, RBC removal
DEA 8 40% Unknown

Current blood typing identifies the six most significant antigens: 1.1, 1.2, 3, 4, 5, and 7.

A universal donor is one that is negative for DEA 1.1, 1.2, 3, 5, and 7 and is positive to DEA 4. 

DEA 1 system is the most antigenic and the group that causes the most severe reactions. DEA 1 has three allelic subtypes; 1.1, 1.2, and 1.3. The chart below helps explain the allelic system. DEA 1.1 positive dogs are always negative for 1.2 and 1.3. DEA 1.1 negative dogs can either be 1.2 negative or positive.

If the dog types DEA 1.1: It will type 1.2: It will type 1.3: 


Negative or Positive 

Negative or Positive 




Canine Blood Typing

Commercial blood typing kits are made available for in-house typing. These card tests type for DEA 1.1 only.

There are some limitations to these tests including false negative results, and hard to interpret results from auto-agglutination or extremely low hematocrit (>10%). In the cases where a blood type cannot be determined, universal blood should be given. Dogs that type positive for DEA 1.1 should receive positive or universally negative blood. Dogs that type negative for DEA 1.1 should only receive negative blood.

Full blood typing can be done through local laboratories or through national blood services like Midwest Animal Blood Services in Stockbridge, Mich.,or Stormont Laboratories in Woodland, Calif. These labs are able to test out to DEA 7.

There is much debate on the necessity of complete blood typing, but most transfusion specialists recommend using universal blood especially in IMHA (immune-mediated hemolytic anemia) animals where cross-matching may be difficult and multiple transfusions may be needed.

Feline Blood Types

There are three known feline blood types: A, B and AB. Type A blood is the most common, occurring in 95 percent to 97 percent of the general cat population. Type B occurs in approx 2 percent to 5 percent of the feline population and is more common in exotic breed cats (devon rex, British shorthair, cornish rex, exotic shorthair, and Scottish folds). Type AB occurs in less than 1 percent of the population and is considered extremely rare.

Type A cats may have weak anti-B alloantibodies, however Type B cats have very strong anti-A antibodies and can have a fatal reaction if given A blood. Even 1ml of A blood to a B can be fatal. Type AB cats have no alloantibodies to either type A or B. They should, however, receive type AB blood if available or Type A blood.

Feline Blood Typing

As with the canine, commercial feline blood-typing cards are available for in-house testing.

Another quick and affordable way to type cats is a typing procedure using known Type B serum. Because Type B cats have such strong antibodies to Type A blood, one drop of Type B serum can be added to one drop of the patient’s blood to determine blood type status.

If the patient is Type A you will see immediate gross agglutination. If the patient is Type B you will see no agglutination. The slide should be checked under a microscope to confirm the results.


The cross-match is used to determine incompatibility between donor and recipient. It can recognize antibodies to either known or unknown antigens.

The major cross-match is between the donor cells and the recipients plasma while the minor cross-match is between the donor plasma and the recipient cells.

Incompatibility in the major cross-match means a reaction is likely and the donor should not be used. While it’s better to use blood that is compatible on the minor cross-match, it is less important because the donor’s plasma is a small volume and will become diluted in the recipient’s body.

Cross-matching should always be done if:

Animals can still have reactions even with a compatible cross-match because of reactions from white blood cells, platelets and other proteins.

Cross-match Procedure

  1. Obtain an anticoagulated (EDTA) sample from both patient and donor.
  2. Centrifuge and separate plasma from red blood cells at standard blood speed.
  3. Remove plasma from the red cells and place in red-top tube that is clearly marked plasma.
  4. Remove remaining packed red cells from the bottom of tube and place in an additional red-top tube clearly marked red cells.
  5. Fill the tube ¾ full with sterile saline. Mix gently and centrifuge for one minute.
  6. Decant the saline and repeat step 5 three more times. This is known as cell washing and helps to free the cells of proteinaceous debris.
  7. After the last wash, decant the supernatant.
  8. Re-suspend the cells with saline to give a 2 percent to 4 percent suspension of RBC. It should look like “weak” tomato juice.  
  9. Make the following mixtures by adding the RBC suspension and plasma to new red- top tubes. 
                            Major Crossmatch Minor Crossmatch Control  
    Patient 2 drops plasma  1 drop 2-4% RBC 1 drop
    Patient   Suspension 2-4% with RBC suspension with 2 drops
    Donor 1 drop 2-4% RBC 2 drops plasma patient
    Plasma Suspension    
  10. Incubate tubes for 20 to 30 minutes at 37 degrees C.
  11. Centrifuge for 15 seconds. 

Interpreting the Results

Macroscopic. Examine the tubes for hemolysis by gently rolling the tubes between your fingers and observing cells for hemagglutination as they come off the “button” in the bottom of the tube.

Microscopic. Place a drop on a slide with a coverslip and look under the microscope at 10x and 40x for agglutination.

One common mistake in the microscopic exam is confusing the presence of Rouleaux for agglutination.

Rouleaux is normal in some animals and appears as stacked coins; the red cells are stacked on top of each other–this is not agglutination. True agglutination appears as “grape clusters”–the red cells are sticking to each other in clumps in an unorganized fashion.

Rouleaux should disperse as saline is added to the slide, and true agglutination will remain.

For related stories, click on any of the following:

Vet Blood Banking Endures Growing Pains[1]

Oxyglobin Buys Time While Awaiting Blood[2]

Blood Typing and Cross-matching[3]

Veterinary Blood Banks Keep Supplies Flowing[4]


Author’s note: New information is out on feline blood types. Type AB is rare but more common than thought in the past.  If you have a cat that is possibly a type AB, you can give type A blood. Type AB is so new that you can’t by AB blood from a commercial veterinary blood bank yet and getting a confirmed blood type test done at a lab for Type AB is not yet possible.


  1. Davidow, Beth. Transfusion Medicine. ACCES, Seattle, WA. 2003.
  2. Day, M, Mackin A, Littlewood, J. Manual of Canine and Feline Haematology and Transfusion Medicine. BSAVA, 2000.
  3. Giger U. Recent Advances in Canine Transfusion Medicine: Blood Typing and Crossmatching to Ensure Compatible Transfusions. Proceedings IVECCS VI; 1998: 191-193.
  4. Oakley DA, Giger U. Veterinary Blood Banking: Can we meet the standards? Proceedings IVECCS VI; 1998: 194-197.
  5. Wardrup KJ, Hale AS. New developments in canine and feline transfusion medicine: blood typing and crossmatching. Proceedings 16th ACVIM Forum 1998: 589-591.
  1. Vet Blood Banking Endures Growing Pains: /April-2009/Vet-Blood-Banking-Endures-Growing-Pains/
  2. Oxyglobin Buys Time While Awaiting Blood: /April-2009/Oxyglobin-Buys-Time-While-Awaiting-Blood/
  3. Blood Typing and Cross-matching: /April-2009/Blood-Typing-And-Cross-matching/
  4. Veterinary Blood Banks Keep Supplies Flowing: /April-2009/Veterinary-Blood-Banks-Keep-Supplies-Flowing/

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