Page 1030 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

CHAPTER 9

HAEMOLYMPHATIC SYSTEM
VetBooks.ir Darren Wood and Sonya Keller 1005

Diseases or abnormalities of the haemolym- should be obtained, as the ratio of anticoagulant to
phatic system are often encountered in equine blood is important for valid results.
medicine. Evaluation of the blood-forming Samples for a complete blood count (CBC)
organs and lymphatic tissues can provide infor- should be analysed as quickly as possible and
mation as diverse as bone marrow integrity, refrigerated at 4°C if a delay beyond 2 hours is
cellular response to infection, haemostasis com- expected. Blood smears should be made immedi-
petency and immune system status. A thorough ately and submitted with the remaining blood on
evaluation of the system using blood and tissue cold packs for automated analysis. Refrigerated
samples may result in a definitive diagnosis or blood should be analysed within 24 hours. After
give useful therapeutic and prognostic guidance collection, tubes of equine blood that are allowed
for systemic diseases secondarily affecting these to sit for any length of time quickly separate and
tissues. red blood cells (RBCs) sediment to the bottom of
the tube. This is due to the marked rouleaux for-
DIAGNOSTIC TESTS mation in horses. Samples should be thoroughly
mixed by inverting the tube gently several times
Blood collection prior to analysis.
The large size of blood vessels in the horse makes
collection of blood samples relatively easy, even in
foals. The jugular vein is most commonly used. 9.1
Other veins that may be accessed include the saphe-
nous, lateral thoracic and cephalic veins. Blood
should be taken only when the animal is calm, as
excitement may induce physiological alterations in
cell counts.
Anticoagulated whole blood is required for evalu-
ation of the haematological system. Blood for this
purpose is most commonly collected in evacuated
tubes containing ethylenediaminetetraacetic acid
(EDTA) that binds calcium, making it unavail-
able for the blood clotting process. Citrate, which
is also a calcium-chelating agent, is the preferred
anticoagulant for coagulation assays. Heparin may
also be used to collect whole blood and can be used
for blood-gas analysis and some biochemical assays.
Heparinised blood is not suitable for haematologi-
cal analysis since platelets frequently clump and the Fig. 9.1 Three blood tubes. From left to right: purple
morphology of leucocytes is altered (Fig. 9.1). With top tube (EDTA), red top tube (no anticoagulant), blue
any collection tube, the appropriate volume of blood top tube (citrate).