Page 520 - Problem-Based Feline Medicine

512 PART 7 SICK CAT WITH SPECIFIC SIGNS

hours of collection and stored for < 1 year), or 2 units Transmission
cryoprecipitate.
Factor VIII deficiency is a heritable single-gene defect
● By definition, fresh products are those used
that is X-linked recessive.
within 8 hours of collection. Factor VIII levels
begin to decline after 8 hours of refrigeration, and Based on classical mendelian inheritance, where “X”
in humans only 50% of factor VIII activity is pres- and “Y” are sex-chromosomes, “H” is the normal fac-
ent after 24 hours, but in dogs 85% of activity tor VIII gene, “h” is the abnormal factor VIII gene, and
remains. Some factor VIII activity is probably pres- approximately half the litter are males and half females:
ent in both up to two weeks. The stability of feline ● Breeding an unaffected male (X ,Y) to a normal
H
factor VIII is not known. While ideally fresh blood female (X ,X ), will result in all normal males and
H
H
products should be used, blood or plasma that is all normal females, i.e. none in litter are bleeders.
more than 8 hours old is still likely be beneficial to This is, of course, the normal situation.
H
a hemophiliac. ● Breeding an unaffected male (X ,Y) to a carrier
H
● If plasma products are used, 25–70 ml packed red female (X ,X ), will result in 50% of the males in
h
cells may also be needed. the litter being affected, and 50% of the females
● Transfusion may be used during a bleeding episode being carriers, i.e. approximately 25% of the litter
or prophylactically before a procedure. (all males) are bleeders. This is the most likely nat-
● Collect sufficient blood samples for hemostatic ural scenario in the random appearance of hemo-
testing prior to transfusion. philia.
H
● A single transfusion may stop active bleeding in a ● Breeding an unaffected male (X ,Y) to an affected
h
cat if there is no underlying injury or inflammatory female (X ,X ), will result in all males being
h
disorder. affected and all females being carriers, i.e. approxi-
● Half-life of factor VIII post-transfusion is probably mately 50% of litter are bleeders (all males).
only 8–12 hours, so repetitive transfusions every ● Breeding an affected male (X ,Y) to a normal
h
H
12–24 hours may be necessary. female (X ,X ), will result in all males being nor-
H
● Cats with absolute factor VIII deficiency may theo- mal and all females being carries, i.e. none in litter
retically become refractory to transfused factor VIII are bleeders.
h
because of antibody formation. ● Breeding an affected male (X ,Y) to a carrier
H
h
female (X ,X ), will result in 50% of the males
Treatment with vitamin K1 is of no benefit, except as a
being affected, and 50% of the females being
diagnostic test to rule out vitamin K antagonist poison-
affected females, i.e. 50% of litter are bleeders (half
ing.
male, half female).
h
Treatments in dogs and/or humans not evaluated in cats ● Breeding affected male (X ,Y) to an affected
h
include desmopressin, lyophilized factor VIII, recombi- female (X ,X ), will result in all males being
h
nant human factor VIII, recombinant factor VIIa, affected and 50% all females being affected, i.e.
inhibitors of fibrinolysis (e.g. aminocaproic acid), liver 75% in litter are bleeders (all male, half female).
transplantation, and gene therapy. This is the least likely naturally occurring situation.
Prognosis
Prevention
In most cases spontaneous bleeding is minimal or
Parents and littermates may be tested for factor
mild.
VIII:C to identify affected cats (males and homozy-
Prognosis is good for cats kept in an environment gous females) and carriers (heterozygous females).
that minimizes trauma and exuberant exercise. ● Normal cats have normal factor VIII:C levels.
● In most species, carrier females have ≈ 40–60%
Bleeding tendency appears to be less in mature cats
normal factor VIII:C, but the upper range may
compared to juveniles. An explanation for this may be
overlap with the lower range of normal. One con-
factor VIII levels increasing with age, as has been seen
firmed carrier had a factor VIII:C of 69%. Breeding
in normal cats.