Page 1418 - Small Animal Internal Medicine, 6th Edition

1390 PART XIII Hematology

platelet clumping commonly results in pseudothrombo- As mentioned earlier, evaluation of the RBC dot plots in
cytopenia. Next the oil immersion lens should be used a LaserCyte or ProCyte Dx Hematology Analyzer (IDEXX
VetBooks.ir to examine several representative monolayer fields (i.e., Laboratories, Westbrook, ME) also provides valuable infor-
mation on platelet numbers and clumping. For a discussion
where approximately 50% of the red blood cells [RBCs]
touch each other), and the number of platelets in five fields
The second set of point-of-care tests of hemostatic func-
should be averaged. In dogs, 12 to 15 platelets should be of dot plot evaluation, see Fig. 87.1.
present in each oil immersion field; in normal cats, 10 to tion are the ACT, OSPT, and aPTT. For the aPTT, 2 mL of
12 platelets per field should be seen. As a general rule, whole fresh blood (WFB) is added to a tube containing dia-
each platelet in an oil immersion field represents 12,000 to tomaceous earth; this activates the contact phase of coagula-
15,000 platelets/µL (the number of platelets/oil immersion tion, thus assessing the integrity of the intrinsic and common
field × 15,000 = platelets/µL). Cats and dogs with plate- pathways (factors I, II, V, VIII, and IX to XII; see Fig. 87.2).
let counts of >30,000/µL and normal platelet function do If the activity of individual clotting factors involved in these
not bleed spontaneously. Therefore the cause of bleed- pathways has decreased by more than 70% to 75%, the ACT
ing is usually not thrombocytopenia if more than two or is prolonged (normal, 60-90 seconds). Common coagulopa-
three platelets are visualized in each oil immersion field. thies associated with prolongation of the ACT are listed in
The evaluation of platelet numbers should also include Table 87.2. This test is rarely done today because of the avail-
evaluation of the morphology of individual platelets be- ability of simple point-of-care instruments.
cause abnormal platelet morphology may reflect impaired We routinely use a point-of-care instrument in dogs
platelet function. and cats (Coag Dx Analyzer, IDEXX Laboratories). This

NORMAL RBC RUN (Canine)

Size Size

DOT PLOT LEGEND
RBC_FRAG WBC
RETICS PLT
RBC
A Fluorescence B Fluorescence
NORMAL WBC RUN (Canine)

Fluorescence Fluorescence

DOT PLOT LEGEND
URBC NEU
LYM BASO
C Granularity D Granularity MONO EOS

FIG 87.1
Dotplots from a dog with pseudothrombocytopenia (A and C), and the same dog after
obtaining a new blood sample (B and D) obtained with a ProCyteDx hematology
analyzer. In the red blood cell graphics, note the lower density of platelet (blue circle) in
panel A, compared with B (new blood sample). In the leukocyte graphics please note the
curvilinear “cloud” (orange arrows) in panel C that represents platelet clumping and is no
longer present in panel D (new sample). Normal RBC and WBC graphics are provided in
the right. BASO, Basophils; EOS; eosinophils; LYM, lymphocytes; MONO, monocytes;
NEU, neutrophils; PLT, platelets; RBC, red blood cells; RBC_FRAG, red blood cell
fragments; RETICS, reticulocytes; URBC, unlysed red blood cells; WBC, white blood cells.