Page 1421 - Small Animal Internal Medicine, 6th Edition

CHAPTER 87 Disorders of Hemostasis 1393

a simple, cage-side instrument for evaluating platelet adhe- BOX 87.3
sion and aggregation. This instrument is available in several
VetBooks.ir specialized clinical hemostasis laboratories and has been Congenital and Acquired Clotting Factor Defects
extensively evaluated in dogs. The PFA-100 is sensitive for
Congenital Clotting Factor Defects
the screening of vWD. The Thromboelastograph Hemosta-
sis Analyzer system (TEG; Haemonetics, Braintree, MA), Factor I, or hypofibrinogenemia and dysfibrinogenemia
also available in several specialized hemostasis laboratories, (Bichon Frise, Borzoi, Collie; DSH)
uses native or anticoagulated blood activated with a variety Factor II, or hypoprothrombinemia (Boxer, Otterhound,
of agonists. This instrument evaluates global hemostasis, English Cocker Spaniel)
including platelet adhesion and aggregation, fibrin forma- Factor VII, or hypoproconvertinemia (Alaskan Klee Kai,
Beagle, Malamute, Scottish Deerhound, Schnauzer; DSH)
tion, fibrinolysis, and clot retraction. The TEG is ideal to Factor VIII, or hemophilia A (many breeds but mainly
monitor response to blood component therapy in patients German Shepherd Dogs and Golden Retrievers; DSH)
with coagulopathies. I have found that it provides a wealth Factor IX, or hemophilia B (many breeds of dogs; DSH
of information in patients with hypercoagulability and those and many cat breeds)
with spontaneous bleeding and normal results of hemostasis Factor X, or Stuart-Prower trait (Cocker Spaniel, Jack
profiles. Platelet mapping is a new TEG-based method that Russell Terrier; DSH)
allows the titration of antiplatelet agents in humans; we have Factor XI, or hemophilia C (English Springer Spaniels,
found it to be very reliable in dogs. However, this analyzer Great Pyrenees, Kerry Blue Terriers; DSH)
requires a fresh (<2 hours) blood sample, so the patient Factor XII, or Hageman factor (Miniature Poodles, Shar
likely needs to be referred to the center where the tests will Pei; DSH, DLH, Siamese, Himalayan cats)
be conducted. Prekallikrein (Fletcher factor) deficiency (various dog
breeds)
As noted, if an unusual coagulopathy or specific clotting
factor deficiency is suspected, blood should be submitted to Acquired Clotting Factor Defects
a specialized veterinary coagulation laboratory. Congenital Liver disease
and acquired clotting factor deficiencies that occur in cats Decreased production of factors
and dogs are listed in Box 87.3. Qualitative disorders?
Thrombocytopenia can be caused by decreased produc- Cholestasis
tion or increased destruction, consumption, or sequestration Vitamin K antagonists (rodenticides)
of platelets; therefore a bone marrow aspiration for cytologic
evaluation is indicated in cats and dogs with thrombocyto- DIC
penia of unknown cause. Other tests can also be performed DIC, Disseminated intravascular coagulation; DLH, domestic
in thrombocytopenic cats and dogs, including determina- long-haired cat; DSH, domestic short-haired cat.
tions of titers or a polymerase chain reaction (PCR) assay for Modified from Brooks MB: Hereditary coagulopathies. In Weiss DJ,
vector-borne diseases, or evaluation for retrovirus infection Wardrop KJ, editors: Schalm’s veterinary hematology, ed 6, Ames,
(see Chapters 91 and 96). Iowa, 2010, Wiley-Blackwell, p 661.
Finally, clinicians occasionally encounter a patient with
abnormal results of hemostasis profiles but without sponta-
neous bleeding. The most common abnormality in the anticoagulants is to perform an aPTT after diluting the
hemostasis profile of a dog or cat without a tendency to bleed patient’s sample 50:50 with normal or pooled dog plasma
is a prolongation of the aPTT. Often the prolongation is (dilution assay). As noted, the aPTT becomes prolonged
marked (>50% above the control or upper limit of the refer- when the patient has less than 30% activity of an individual
ence range for the laboratory). If this abnormality is found factor. If the patient has factor XII deficiency, for example,
during a presurgical evaluation, the surgery may be delayed and 0% factor XII activity, mixing the sample 50:50 with
needlessly if the clinician is not familiar with some of the normal dog plasma (with a factor XII activity of 100%) will
following clinical conditions. As noted, dogs and cats with result in a final factor XII activity of 50% and thus the aPTT
factor XII deficiency do not bleed but have a prolonged will be normal. Circulating anticoagulants also inhibit the
aPTT; determination of factor XII activity will provide a clotting factors in normal dog plasma, so when the samples
diagnosis. Prekallikrein and HMWK are co-factors for the are mixed 50:50, the aPTT remains prolonged. Recently, the
contact activation of factor XII. Dogs with prekallikrein or presence of prolonged aPTT and antiphospholipid antibod-
HMWK deficiencies have prolonged aPTT but do not bleed; ies was documented in healthy Bernese Mountain dogs
incubation of the plasma samples for a few hours overrides (Nielsen et al., 2011a and b).
the factor deficiency and corrects the aPTT. Finally, the pres-
ence of circulating anticoagulants, also referred to as lupus MANAGEMENT OF THE
anticoagulants or antiphospholipid antibodies, results in BLEEDING PATIENT
prolongation of the aPTT without bleeding. A simple test to
determine whether the patient with a prolonged aPTT has a Several basic principles apply to the management of cats
clotting factor deficiency (e.g., factor XII) or circulating and dogs with spontaneous bleeding disorders. Specific