Page 201 - Basic Monitoring in Canine and Feline Emergency Patients

Table 9.2. Interpretation of the relative degrees of PT and PTT prolongation.

VetBooks.ir PT aPTT Interpretation
Suggests extrinsic arm of the coagulation cascade (see Fig. 9.1)
Normal or
Prolonged >2–2.5
times the high end of
<2 times the high
the normal range prolongation primarily affected
• Anticoagulant rodenticide intoxication, relatively early in
end of the normal course of disease a
range • Liver failure, relatively early in course of disease a
Factor VII deficiency
Normal or prolongation Prolonged >2–2.5 Suggests intrinsic arm of the coagulation cascade (see Fig. 9.1)
<2 times the high times the high end primarily affected
end of the normal of the normal range • Factor XII deficiency
range • Factor XI deficiency
• Factor IX deficiency
• Factor VIII deficiency
Disseminated intravascular coagulation (multiple factors)
Prolonged >2–2.5 Prolonged >2–2.5 Suggests intrinsic and extrinsic arms of the coagulation cascade
times the high end of times the high end (see Fig. 9.1) both affected b
the normal range of the normal range • Anticoagulant rodenticide intoxication (usually PT
prolongation is still a greater magnitude than aPTT due to
short half-life of factor VII)
• Liver failure (usually PT prolongation greater magnitude
than aPTT due to short half-life of factor VII)
Disseminated intravascular coagulation (usually aPTT
prolongation greater magnitude than PT due to consumption
of clotting factors involved in amplication/propagation [VIII, IX]
more than those involved in initiation [factor VII and TF])
aPTT, activated partial thromboplastin time; PT, prothrombin time; TF, tissue factor.
a Factor VII has the shortest half-life of all the coagulation factors and is found in the extrinsic arm of the coagulation cascade.
Therefore, early in the course of disease, PT prolongations occur first.
b When both values are greatly prolonged, especially when PT alone or both PT/aPTT are off the analyzer’s scale, the animal has
anticoagulant rodenticide intoxication until proven otherwise.

these precautions, platelets (especially in cats) may While most blood samples for platelet/CBC analy-
clump regardless, making a manual review of all sis are collected into EDTA anticoagulant, citrated
blood smears in all species necessary to assess for samples can also be used. However, the larger liquid
this artifact. Rough manual estimates made during volume of the citrate will cause minor dilution of the
slide review can be interpreted as a minimum plate- blood compared to the reference intervals calcu-
let count (see Section 9.2), although the actual lated from EDTA samples. Multiplying the platelet
platelet count may exceed that range. concentration measured on the CBC by 1.1 will
Large platelets (such as those commonly seen correct for the dilution. Heparinized samples are not
in Cavalier King Charles Spaniels) may exceed recommended for platelet counts as platelet clump-
the upper size threshold for platelets on some ing is expected with this anticoagulant.
impedance analyzers and therefore may be mis- Some breeds of dogs such as Greyhounds and
counted as other cells. Similarly, excessive plate- Cavalier King Charles Spaniels have a lower
let clumping may be misinterpreted by automated platelet count naturally. Unless these patients also
analyzers; the platelet clumps may be counted as have clinical signs of a primary hemostatic disor-
neutrophils, basophils, or eosinophils. The misin- der (see Section 9.3) or significantly low platelet
terpretation of platelet clumps is less of an issue counts (<50,000/μL), clinicians should make sure
in most modern analyzers which recognize sus- they are using breed-specific cutoffs for thrombo-
pected clumping and flag the results for the opera- cytopenia before initiating a significant diagnos-
tor to review. tic workup.

Coagulation 193