Page 1033 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1008 CHAPTER 9

VetBooks.ir Evaluation of coagulation functional proteins of the tissue factor (extrinsic)
and common pathways of the coagulation cascade
Citrated plasma is used for routine functional assess-
ments of coagulation (Fig. 9.6). Prothrombin time
(PT) and activated partial thromboplastin time to form an in-vitro clot. A normal APTT indicates
the presence of adequate functional proteins of the
(APTT) are the most common tests performed. contact activation (intrinsic) and common path-
A normal PT indicates the presence of adequate ways to form an in-vitro clot. Other assays include
fibrinogen quantitation, thrombin clotting time and
indicators of fibrinolysis, such as fibrin degradation
9.6 products (FDPs) and d-dimers.
Intrinsic pathway Extrinsic pathway
(platelet factors) (tissue factors)
Immunohaematology
XI VII A crossmatch is a laboratory procedure that deter-
XII III III mines the compatibility of donor and recipient cells.
IX Crossmatching is most often performed for horses
requiring a transfusion of RBCs because of severe
Prothrombin time (PT)
Activated clotting time VIII anaemia. A major crossmatch determines whether the
(ACT) recipient has naturally occurring serum antibodies to
X antigens on the donor’s RBCs. Antibody binding is
Partial thromboplastin indicated by agglutination (Fig. 9.7), haemolysis or a
time (APTT)
Coombs test. A minor crossmatch assesses whether
V
Common pathway II Thrombin time (TT) donor’s serum and is not often performed.
the recipient’s erythrocytes form complexes with the
Blood typing is an assessment of the antigens pres-
ent or absent on the surface of an individual’s RBCs
I or lymphocytes. There are several RBC groups (or
systems) in the horse that define alloantigens for this
species, including A, C, D, K, P, Q and U. Blood
typing is used for predicting the occurrence of neo-
natal isoerythrolysis (NI), analysing pedigree and
Fibrin clot
identifying animals.
Fig. 9.6 Diagram of the coagulation pathways, clotting The Coombs test is performed to confirm
factors and routine tests used to assess the system. the presence of antibody on the surface of RBCs
(Fig. 9.8). The Coombs reagent is composed of
9.7 antibodies to species-specific immunoglobulins and
complement C3. A positive test can be observed in
animals with immune-mediated haemolytic anaemia
(IMHA), NI and equine infectious anaemia (EIA)
virus infection. The test is performed on EDTA
anticoagulated blood.

Protein determination
Total protein concentration or a more detailed
assessment of individual proteins can be deter-
mined by various methods. Total plasma protein
Fig. 9.7 Major crossmatch. The upper test tube is determination by refractometry is the simplest
the negative control (no agglutination) and the lower method available and provides a reasonable estimate
test tube is a strongly positive result (agglutination of all the proteins in a clear specimen (Fig. 9.9).
present), indicating an incompatible crossmatch. Excess turbidity or lipaemia may interfere with the