Page 325 - The Veterinary Laboratory and Field Manual 3rd Edition

294 Susan C. Cork and Roy Halliwell

brown). Compare the colour to that produced Generally, because of mechanical factors, a high
by a titrated preparation of the standard. PCV is associated with a low ESR. Equally a low
PCV may be associated with an elevated ESR.
cyanMEtHaEMoGLobIn MEtHod
For this method a colorimeter is required along Method
with a standard haemoglobin solution and
Drabkin’s reagent. Fill a Wintrobe haematocrit tube with blood to
the top of the 100 mm scale and place in a verti-
Drabkin’s reagent: cal position at room temperature. The level to
which the top of the RBC column falls in exactly
Potassium cyanide (KCN) 0.05 g
one hour is recorded as the observed ESR.
Potassium ferricyanide (K Fe (CN) ) 0.20 g
2 6
Distilled water 1000 ml (1 l). Interpretation ](simplified)
The rate of settling is influenced by: (1) species;
This reagent is stable for 1 month. Store in a (2) the number of red cells (that is, PCV); (3)
stoppered bottle and label. Note that cyanide the concentration and composition of plasma
compounds are toxic so handle with care. proteins, that is, the ESR is often high in chronic
Add 0.02 ml of blood to 4 ml of Drabkin’s disease due to the increased amount of fibrino-
reagent in a stoppered bottle. Mix by inver- gen and gamma globulins; (4) the maturity of the
sion two or three times and allow to stand erythrocytes, that is, reticulocytes and immature
for 10 min. Compare against a commercially red cells exhibit a greater tendency to clump or
available standard in a colorimeter. Most haemo- form chains (rouleaux formation) than mature
globin standards have a concentration of 12.0 g or red cells; and (5) physical factors such as cleanli-
16.0 g/100 ml (12 g/dl or 12%). If available, mod- ness of pipettes, the position of the ESR tubes,
ern colorimetric techniques can also be used, for vibrations, ambient temperature and so on.
example the Diaspect Tm handheld haemogobi-
nometer described in Chapter 2 (Figure 2.45).
5.5 Collection and examination of
smears from bone marrow
Erythrocyte sedimentation rate
The primary function of bone marrow is the
The rate at which RBC settle in a set time is production of red blood cells, granulocytes
known as the erythrocyte sedimentation rate (neutrophils, basophils and eosinophils),
(ESR). The ESR is influenced by a number of fac- agranulocytes and the precursors of thrombo-
tors, for example, the number of immature red cytes (platelets). Active bone marrow is red
cells present, rouleaux formation, the presence and resting marrow is yellow in colour. In new-
of abnormal cells and so on. In some species it is born animals, most of the bone marrow tissue
used as a guide to the effectiveness of long-term is red marrow and is actively producing blood
therapy, for example, in cases of inflammatory cells. In adults, yellow marrow fills much of the
disease. In order to fully evaluate the signifi- bone cavity space in the long bones (those of
cance of the ESR it is important to consider it the limbs) but this may convert to red marrow if
in reference to the PCV and the species (for the demand for red cell production increases as
example, horses tend to have a higher ESR). in blood loss and chronic anaemia. The flat bones

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