Page 323 - The Veterinary Laboratory and Field Manual 3rd Edition

292 Susan C. Cork and Roy Halliwell

column of red cells is expressed as a percentage breakage. Wipe the outside of the tube and seal
of the total volume of the blood in the tube. the ends using sealant (or seal the free end in a
After the tubes have been spun there will be flame). Make sure that the tubes are well sealed
three layers: to prevent leakage. Place the tubes in a micro-
haematocrit centrifuge opposite each other and
1 a bottom red layer of compacted red blood (where several samples are handled together)
cells take note of the position of the haematocrit
2 a middle whitish layer (the buffy coat) of tube(s). Most divisions in the haematocrit rotor
white blood cells and platelets will be numbered. If the tubes are not well posi-
3 a top clear to pale yellow layer containing the tioned or the rubber insulating material around
plasma (serum + clotting proteins). the inside edges of the haematocrit rotor is worn
the tubes may break so check this before secur-
From the PCV result using this method a rough ing the lid of the unit. Centrifuge the samples
estimate of other parameters can be made as at 12,000 g for 4 min. After centrifugation note
follows: that there are two obvious layers, the buffy coat
is less readily detected in this method than with
PCV = 45 % the Wintrobe method. Make sure that there is no
haemolysis or clotting of the sample. Measure
Normal Haemoglobin (Hb) = 1/3 PCV
(45%) = 15 g/dl the height of the red cell column using a hae-
matocrit reader (often provided on the lid of a
Normal erythrocyte count (TRCC) = 1/6 haematocrit centrifuge).

PCV × 10 = 7.5 × 10 /µl
6
6
Leukocytosis (high TWCC) = 1.5 mm or
greater in the Wintrobe tube determination of haemoglobin
content
Leukopaenia (low TWCC) = 0.5 mm or less
in the Wintrobe tube Haemoglobin is the red pigment contained in
red cells. This pigment is important in the trans-
Cloudy plasma = lipaemic (fatty blood)
fer of oxygen to body tissues. The measurement
Dark yellow plasma = jaundice (bile pig- of haemoglobin is usually recorded as grams
ments in the blood) per 100 ml of blood. There are various meth-
ods used to measure the haemoglobin level in
Note that a high PCV may indicate dehydration. blood samples and most depend on measuring
Dehydration can therefore mask anaemia. the intensity of colour produced by haemoglo-
bin. One of the simplest methods is Sahli’s acid
MIcroHaEMatocrIt MEtHod haematin method as it requires little equipment
For this method capillary tubes, sealant and a and is easy to perform.
microhaematocrit centrifuge (at 12,000 g) will This method is, however, subjective and has a
be required along with a calibrated reader (see high degree of error unless performed regularly
Figure 5.5). by the same person. If a colorimeter is available
Fill a pair of capillary tubes with the blood along with a haemoglobin standard the meth-
sample (use EDTA blood) using capillary attrac- ods outlined in the biochemistry section (see
tion until the tube is filled to two-thirds of its Chapter 7) are recommended. The advantage of
length. Paired samples are prepared in case of using a colorimeter is that the results are less

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