J Vet Intern Med 2013;27:1136–1142
Hypercoagulability and ACTH-Dependent Hyperadrenocorticism in
Dogs
F.M. Park, S.L. Blois, A.C.G. Abrams-Ogg, R.D. Wood, D.G. Allen, S.G. Nykamp, and A. Downie
Background: Dogs with hyperadrenocorticism are at risk of thromboembolic disease, which might be caused by an
underlying hypercoagulable state.
Hypothesis/Objectives: To assess hemostatic function in dogs with ACTH-dependent hyperadrenocorticism (ADHAC)
before and after treatment.
Animals: Nineteen dogs with ADHAC and 40 normal dogs.
Methods: Prospective, observational study. Dogs with ADHAC were recruited from the referral hospital patient population; normal dogs were recruited from staff and students at the study’s institution. Hemostasis was assessed before and at 3 and
6 months after treatment with trilostane (T0, T3, T6) by kaolin-activated thrombelastography with platelet mapping (TEGPM), prothrombin time, activated partial thromboplastin time, fibrinogen concentration, and antithrombin activity (AT).
Results: Dogs with ADHAC had statistically significantly increased a-angle (P < .01) and maximum amplitude
(MA)thrombin (P < .01) on TEG-PM, and significantly decreased j (P < .005) at T0, T3, and T6. Platelet count (P < .001)
and fibrinogen concentration (P < .001), but not AT activity, were increased in dogs with ADHAC at T0, T3, and T6.
Conclusions and Clinical Importance: Dogs with ADHAC have thrombelastographic evidence of hypercoagulability and
remained hypercoagulable during treatment. AT deficiency does not appear to be involved in the pathogenesis of hypercoagulability in this population.
Key words: Cushing’s disease; Hemostasis; Platelet; Thrombelastography; Thromboembolism.
CTH-dependent hyperadrenocorticism (ADHAC)
is characterized by chronic hypercortisolemia
secondary to an ACTH-secreting pituitary tumor.1
Hyperadrenocorticism in dogs has been associated with
thromboembolic disease, and thrombi occur in pulmonary veins, splenic veins, aorta, and iliac arteries of
dogs with hyperadrenocorticism.2–6 The exact incidence and risk of thromboembolic disease in dogs with
hyperadrenocorticism have not been defined and the
pathogenesis of thromboembolic disease is incompletely understood. These patients might be hypercoagulable.7 Thrombelastography (TEG) is a point-of-care
test that has been validated in dogs7 and has the
advantage of being able to detect dogs who are hypercoagulable.8–16 However, thrombin generated by standard TEG assays might obscure the contribution of
individual and potentially weaker platelet agonists to
thrombus formation. A modification in TEG, platelet
mapping (TEG-PM), has been developed to separately
analyze the contributions of thrombin, fibrin, and
platelets to clot formation. The contribution of the
platelet agonists adenosine diphosphate (ADP) and
A
From the Departments of Clinical Studies (Park, Blois, Abrams-Ogg,
Allen, Nykamp) and Pathobiology (Wood), and Health Sciences
Center (Downie), Ontario Veterinary College, University of Guelph,
Guelph, ON; and Dr Park is presently affiliated with Animal Referral
Hospital, Homebush, NSW. This study was presented in part at the
2012 American College of Veterinary Internal Medicine Forum, New
Orleans, LA.
Corresponding author: S.L. Blois, DVM, DVSc, DACVIM.
Department of Clinical Studies, Ontario Veterinary College,
University of Guelph, Guelph, ON, N1H 2B2; e-mail: sblois@
uoguelph.ca.
Submitted January 18, 2013; Revised May 23, 2013;
Accepted July 16, 2013.
Copyright © 2013 by the American College of Veterinary Internal
Medicine
10.1111/jvim.12162
Abbreviations:
AA
ADHAC
ADP
aPTT
AT
CL30
G
LDDST
MA
PT
R value
SBP
TEG-PM
TEG
UPCR
arachidonic acid
ACTH-dependent hyperadrenocorticism
adenosine diphosphate
activated partial thromboplastin time
antithrombin
clot lysis at 30 minutes
global clot strength
low-dose dexamethasone suppression test
maximum amplitude
prothrombin time
reaction value
systolic blood pressure
thrombelastography platelet mapping
thrombelastography
urinary protein-to-creatinine ratio
arachidonic acid (AA) to platelet activation can be
individually assessed with results reported as maximum
amplitude (MA)ADP and MAAA. Fibrin clot strength
in the absence of platelet activation is assessed as a
baseline (MAfibrin). A standard kaolin-activated TEG
assay assesses the maximum clot strength for that
patient (MAthrombin).17 In healthy dogs receiving
clopidogrel treatment, MAADP correlated with ADPinduced platelet aggregation measured by impedance
aggregometry.18
The objective of this prospective longitudinal study
was to assess dogs with ADHAC for evidence of
hypercoagulability before and after treatment with trilostane, using TEG-PM as well as conventional hemostatic tests including prothrombin time (PT), activated
partial thromboplastin time (aPTT), and fibrinogen
concentration. In addition, urinary protein-to-creatinine ratio (UPCR), plasma antithrombin (AT) activity,
and systolic blood pressure (SBP) were evaluated
ACTH-Dependent Hyperadrenocorticism
to examine the possible relationship between urinary
protein loss and hypertension with coagulation status.
Materials and Methods
Animals and Study Design
This study was performed at the University of Guelph between
November 2009 and October 2011, in accordance with the standards of the Canadian Council on Animal Care and the Ontario
Animals for Research Act. Informed consent was obtained from
all dog owners and the study was approved by the University of
Guelph Animal Care Committee.
Forty healthy control dogs, between the ages of 1 and
11 years, were recruited to determine reference intervals and used
as a control group. The dogs were deemed healthy on the basis
of physical examination, complete blood count (CBC), serum
biochemical profile, and urinalysis. The dogs had not received
any medications, excluding heartworm and flea prophylaxis, in
the preceding 6 weeks.
Nineteen client-owned dogs with ADHAC that had not
received previous treatment for hypercortisolism were included in
the study. Exclusion criteria included a previous diagnosis of
chronic kidney disease, diabetes mellitus, malignant neoplasia,
hepatic insufficiency or congestive heart failure, and treatment
with nonsteroidal anti-inflammatory agents or anticoagulant
medications in the previous 6 weeks. Hyperadrenocorticism was
suspected on the basis of consistent clinical signs, history, and
physical examination features, as well as if patients displayed at
least 3 of the following 5 clinicopathological findings: elevated
alkaline phosphatase, elevated alanine aminotransferase, elevated
cholesterol, urine specific gravity <1.020, and positive urine bacterial culture. Hyperadrenocorticism was diagnosed if at least 1
of the after 2 screening tests was positive: a supportive low-dose
dexamethasone suppression test (LDDST, 8-hour cortisol
≥1.4 lg/dL [38 nmol/L])19 and ACTH stimulation test (postACTH cortisol concentration >22 lg/dL [600 nmol/L]).20–22
ADHAC was diagnosed if at least one of the following 2 tests
was positive: a supportive LDDST result (4-hour sample
<1.4 mg/dL [38 nmol/L]) or ≤50% of the baseline, or an 8-hour
sample ≤50% of the baseline, but ≥1.4 mg/dL [38 nmol/L]),1,23
and ultrasound showing adrenal glands that were bilaterally
normal or enlarged,24 or in cases of asymmetrical enlargement,
the smaller (contralateral) gland dorsoventral thickness was
>0.5 cm.25 All dogs had adrenal ultrasonography performed by a
board-certified veterinary radiologist (SGN); adrenal glands were
considered to be of normal size if the width was ≤0.75 cm.24
Blood sample collection for evaluation of hemostasis was performed the day before trilostanea administration was started
(T0). The initial trilostane dose was 2–5 mg/kg PO q24h;
response to treatment was assessed after 10–14 days and at
1 month, 3 months (T3), and 6 months (T6). At each recheck, a
physical examination and ACTH stimulation test (2.2 units/kg
ACTH gelb IM, pre-ACTH and 2 hours post-ACTH samples)
were performed. At T0, T3, and T6, CBC, serum biochemistry
profile, PT, aPTT, fibrinogen concentration, TEG-PM, SBP, AT
activity, and UPCR were also obtained. ADHAC was considered
adequately controlled if clinical signs of hypercortisolism had
resolved and post-ACTH cortisol concentration was within the
target interval of 1.4 and 5.4 lg/dL (40–200 nmol/L).
1137
jugular vein was used. Immediately after venipuncture, the
needle was removed from the syringe and blood was transferred
into two 1.8 mL sodium citrate (3.2% citrate [1 volume 0.109 M
citrate to 9 volumes blood] blood collection tubesc ) and one
4 mL heparin (17 IU heparin/mL blood collection tubec) blood
collection tube without vacuum assistance. The SBP was calculated as the mean of 3 readings obtained by the Dopplerd
method as per the American College of Veterinary Internal
Medicine consensus statement26; hypertension was defined as
mean SBP ≥160 mmHg.26 Urine was collected by free catch27 or
cystocentesis.
Laboratory Methods
Prothrombin time, aPTT, and fibrinogen concentratione testing were performed on citrated plasma. The citrated kaolin TEG
and MAfibrin assays (TEG 5000 Thrombelastograph Hemostasis
Analyzerf ) were initiated after sample equilibration for 30 minutes at room temperature.7 For the citrated kaolin TEG assay,
1.0 mL of citrated whole blood was added to a kaolin-coated
vial,f then 340 lL of this sample was added to a TEG cup containing 20 lL of 0.2 M calcium chloride.f Data collected from
citrated kaolin TEG analysis included reaction (R) time, a-angle,
kappa (j), MA, and clot lysis at 30 minutes (CL30). To analyze
MAfibrin, 10 lL of Activator F reagentf was added to a TEG
cup, followed by 340 lL of heparinized blood. After completion
of these 2 assays (approximately 90 minutes after venipuncture),
the MAADP and MAAA assays were initiated. To analyze
MAADP, 10 lL of the Activator F reagent was added to a TEG
cup, followed by 10 lL of the ADP reagent,f then 340 lL of heparinized blood, for a final ADP concentration of 2 lM. A similar
procedure was used to analyze MAAA, with the exception of adding 10 lL of the AA reagent,f giving a final AA concentration of
1 mM. For all assays, TEG cups were prewarmed to 37°C. AT
activity testing was performed by an automated chromogenic
assay, utilizing bovine factor Xa and the chromogenic substrate
S-2765.g Chemistry strip analysis,h specific gravity, sediment
examination, and UPCR were performed on urine samples. Samples were excluded from UPCR measurement when there was
hematuria, pyuria (>5 red or white blood cells per high power
field), or bacteriuria, or if there was a positive urine bacterial
culture.27 UPCR ≥0.5 was considered to represent significant
proteinuria.28
Statistical Analysis
Statistical analysis was performed by statistical software.i To
evaluate whether a standard normal distribution was present, a
Shapiro–Wilk test and examination of the residuals were performed. A general linear mixed model including time and group
as fixed effects, and dog as a random effect, was used to determine if the parameters of interest changed over time or between
groups. Repeated measures made over time on the same animal
were accounted for by fitting different autocorrelation structures.
Posthoc tests were performed when the global testing indicated
differences between groups or time points, and were adjusted by
Tukey’s method. Level of significance was set at P < .05. Correlations were calculated by Spearman’s correlation coefficient.
Data from all time points were included.
Sampling Procedures
Results
Jugular venipuncture was performed with a 20-gauge needle
and 12-mL dry syringe. If the 1st venipuncture did not result in
adequate blood flow, the needle was withdrawn and the opposite
The age of the normal dogs was 4 years (median,
range 1–11 years) and for the ADHAC group at T0, it
was 11 years (range 5–14 years, P < .0001). Four of 19
1138
Park et al
dogs were confirmed to have hyperadrenocorticism by
an ACTH stimulation test and 15/19 dogs by a
LDDST. Two of 19 dogs had both an ACTH stimulation test and a LDDST performed. Seven of 19 dogs
had LDDST results consistent with ADHAC. Eleven
of 19 dogs had sonographically normal adrenal glands,
5/19 had bilaterally symmetrical adrenal enlargement,
and 3/19 had asymmetrical adrenal enlargement with
the smaller gland diameter >0.5 cm.25
Fifteen of 19 dogs with ADHAC were followed up
for the duration of the study and underwent the final
evaluation at T6. Reasons for withdrawal of the other
4 dogs from the study included development of permanent hypoadrenocorticism (1), development of concurrent diabetes mellitus (1), administration of meloxicam
(1), and owner withdrawal (1). No dog was diagnosed
with thromboembolic disease during the study period.
At T3, all of the dogs’ clinical signs had resolved and
13/16 had ACTH stimulation test results within the
target interval. Two dogs required a dosage increase
and 1 dog required a dosage decrease at T3. At T6,
11/15 dogs had ACTH stimulation test results within
the target interval; 1 dog required a dosage increase
and 3 dogs required a dosage decrease. The dose of
trilostane was 2.9 1.1 mg/kg/day (mean SD) at
T0, 3.0 1.2 mg/kg/day at T3, and 3.3 1.4 mg/kg/
day at T6; all dosing was performed once a day.
The dogs with ADHAC had a significantly shorter
PT compared with the normal dogs at all time points
(T0/T3/T6: P < .001; Table 1). The PT did not change
significantly over time in the dogs with ADHAC
(Table 1). At all time points, the dogs with ADHAC
had significantly higher fibrinogen concentration than
the normal dogs (T0/T3/T6: P < .001; Table 1).
Fibrinogen concentration decreased significantly during
treatment of ADHAC (T0–T3: P = .023, T0–T6:
P = .037). The dogs with ADHAC had significantly
higher platelet counts at all time points compared with
the normal dogs (T0/T3/T6: P < .001); platelet numbers did not change significantly over time (Table 1).
Compared with the normal dogs, the citrated kaolin
TEG variables that were significantly different for
ADHAC dogs at all time points included: shorter j
(T0: P = .0022, T3/T6: P < .001), higher a-angle (T0:
P = .0069, T3: P = .0033, T6: P = .0014), and higher
MAthrombin (T0: P < .001, T3: P = .0053, T6: P =
.0025; Table 1). MAthrombin was the only one of these
parameters that significantly changed (decreased) during treatment of ADHAC (T0–T3: P = .020, T0–T6:
P = .042; Table 1). Compared with the normal dogs,
the TEG-PM variables that were significantly different
for ADHAC dogs included: higher MAfibrin at all
time points (T0/T3: P < .001, T6: P = .011), higher
MAADP at T3 (P = .029), and higher MAAA at T0
(P = .019; Table 1). None of these parameters significantly changed during treatment of ADHAC
(Table 1).
Proteinuria was noted in 9/12 ADHAC dogs at T0,
5/9 dogs at T3, and 4/13 dogs at T6; UPCR significantly decreased during treatment of ADHAC (T0–T3:
P = .015, T0–T6: P = .031; Table 1). The UPCR data
were not reported for 6 dogs at T0 and 1 dog at T3
because of the presence of a bacterial urinary tract
infection, an active urine sediment, or both; 1 urine
sample at T3 was misplaced in the laboratory; 5 dogs
at T3 and 2 dogs at T6 did not have urine obtained by
free catch or cystocentesis. Plasma AT activity levels
were measured in 8/19 dogs with ADHAC at T0, in
8/16 dogs at T3, and in 5/15 dogs at T6 (Table 1);
samples were not obtained or sufficient sample volume
Table 1. Selected values for control dogs and ADHAC dogs before treatment (T0) and after 3 and 6 months of
trilostane treatment (T3, T6).
Control
Platelet count (9109/L)
PT (seconds)
aPTT (seconds)
Fibrinogen (g/L)
R (minutes)
Kappa (minutes)
a-angle (°)
MAthrombin (mm)
CL30 (%)
MAfibrin (mm)
MAADP (mm)
MAAA (mm)
UPCR
AT activity (%)
SBP (mmHg)
243
7.6
13.7
1.9
2.9
1.9
64.7
54.4
98.5
5.5
43.1
51.2
(122–487)
(6.0–9.4)
(9.4–43.7)
(1.3–4.4)
(1.7–6.9)
(0.9–3.2)
(50–76.5)
(42.6–71.5)
(88.4–100)
(2.3–68.7)
(3.2–66.2)
(7.4–66.9)
—
—
—
ADHAC T0
464
6.6
14.0
3.9
3.2
1.3
71.2
67.1
100
61.4
58.1
62.8
1.3
93
160
(161–663)a
(5.8–7.2)a
(10.1–35.1)
(2.1–7.0)a
(1.2–8.2)
(0.8–2.0)
(57.0–78.2)a
(50.4–73.3)a
(92.9–100)
(2.7–83.0)a
(7.5–79.1)
(25.1–84.9)a
(0.2–7.1)
(81–114)
(110–227)
ADHAC T3
470
7.0
15.8
3.4
3.2
1.3
72.6
61.0
98.9
62.5
61.7
57.0
0.6
102
140
(90–708)a
(5.6–7.7)a
(11.5–40.3)
(2.0–4.9)a,b
(2.0–4.6)
(0.9–1.8)a
(65.0–76.6)a
(44.8–70.7)a,b
(86.2–100)
(2.5–75.6)a
(5.2–79.6)a
(29.8–70.1)
(0.0–4.7)b
(82–114)
(100–180)
ADHAC T6
401
6.7
16.5
2.9
3.2
1.2
72.9
63.0
98.6
43.6
60.7
56.3
0.25
97
150
(234–881)a
(5.6–7.6)a
(11.7–47.6)
(1.9–5.0)a,b
(1.9–4.2)
(0.8–4.2)a
(48.0–78.4)a
(44.7–70.8)a,b
(85.4–100)
(3.6–67.5)a
(7.3–80.2)
(24.1–70.2)
(0.1–3.9)b
(90–111)
(85–180)
ADHAC, ACTH-dependent hyperadrenocorticism; PT, prothrombin time; aPTT, activated partial thromboplastin time; R, reaction
value; MA, maximum amplitude; CL30, clot lysis at 30 minutes; UPCR, urine protein-to-creatinine ratio; AT, antithrombin; SBP,
systolic blood pressure.
Median (range).
a
Indicates a significant difference to the control group (P < .05).
b
Indicates ADHAC groups at T3 or T6 with a significant difference to T0 (P < .05).
ACTH-Dependent Hyperadrenocorticism
was not stored for the remainder of dogs. Plasma AT
activity was within the laboratory reference interval
with the exception of 1 dog at T3 (114%, RI
75–112%). Plasma AT activity did not change during
treatment of ADHAC (Table 1). Blood pressure was
measured in all dogs at all time points, and hypertension was documented in 10/19 ADHAC dogs at T0,
5/16 dogs at T3, and 6/15 dogs at T6; blood pressure
did not change during treatment of ADHAC
(Table 1).
A moderate positive correlation was identified
between fibrinogen concentration and MAthrombin
(rs = 0.59, P < .0001) in ADHAC dogs. There was a
weak positive correlation between MAfibrin and fibrinogen in ADHAC dogs (rs = 0.38, P = .007) and in
normal dogs (rs = 0.43, P = .006).
Discussion
In this study, dogs with ADHAC had several TEG
variables that were consistent with hypercoagulability,
including increased MAthrombin, decreased j, and
increased a-angle. Dogs with ADHAC remained
hypercoagulable during treatment.
These findings are consistent with previous studies
of iatrogenic hyperadrenocorticism in dogs in which
there were increases in MAthrombin, decreased j, and
increased a-angle29 or increases in MAthrombin alone.30
In contrast with this study, another recent study found
that dogs with hyperadrenocorticism did not have significantly different TEG variables compared with dogs
with nonadrenal illness.31 However, many dogs in the
nonadrenal illness population of that study were
hypercoagulable compared with their institutional
reference intervals.31
Hypercoagulability did not resolve with medical
treatment of ADHAC in this study, in agreement with
a recent study.31 Persistence of hypercoagulability
might explain why thromboembolic disease has been
reported in dogs with controlled hyperadrenocorticism.32 Similarly, resolution of hypercoagulability does
not consistently occur in humans after treatment of
hyperadrenocorticism.33,34 The mean duration of
action of trilostane in dogs is 18 hours,35 meaning that
in dogs dosed once daily, there is potentially a period
of hypercortisolemia for part of each day; this might
be sufficient to ensure ongoing hypercoagulability
despite adequate control of clinical signs of ADHAC.
An alternative explanation could be that irreversible
endothelial dysfunction occurs in these patients. In
addition, 2 dogs at T3 and 1 dog at T6 had postACTH cortisol results higher than the target range for
trilostane treatment. As a result, these dogs might have
been more hypercoagulable than they would have been
if the cortisol concentration had been within the desired
range, potentially influencing the findings of this study.
The increased MAAA in dogs with untreated
ADHAC suggests that increased platelet response to
AA might contribute to hypercoagulability in these
patients. Although the mean MAAA values at T3 and
T6 were also higher than those of the reference interval,
1139
these differences were not significant. Overall, there
was a trend for higher MAADP values in dogs with
ADHAC at all time points compared with normal
dogs, although this only reached significance at T3.
However, there was a large degree of variability
among these results, which might have masked significant changes at T0 and T6. To investigate these findings further, studies should be performed to compare
the results of TEG-PM with other platelet function
tests in dogs with ADHAC. A previous study of dogs
with hyperadrenocorticism showed hypercoagulable
TEG results, but in contrast to this study, platelet hypofunction was documented with a platelet function
analyzer.j The role of platelets in the hypercoagulable
state associated with hyperadrenocorticism at this time
is uncertain. Further studies, including additional
platelet function testing such as aggregometry, are
warranted in this population.
Thrombocytosis was common in this population of
dogs with ADHAC. The mechanism by which glucocorticoids cause thrombocytosis is not well elucidated.
However, glucocorticoids have a permissive effect on
erythropoiesis,36 so it is possible that they have a similar effect on thrombopoiesis. A definitive link between
thrombocytosis and increased risk of thrombosis has
not been made in dogs. The incidence of thromboembolic disease was 7.9% in a group of dogs with
thrombocytosis (platelet count > 600 9 109/L).37 However, most of the dogs had 1 or more underlying systemic diseases, most commonly neoplasia, endocrine
disorders (including hyperadrenocorticism), and inflammatory diseases. As these diseases might be associated
with thromboembolic disease in themselves, it is not
certain whether thrombocytosis or the underlying
diseases themselves lead to these thrombotic events.
The incidence of thromboembolic disease in association with thrombocytosis is similar in humans and is
reported to be 4–6%.38,39
Fibrin clot strength in the absence of thrombininduced platelet activation (TEG-PM MAfibrin) was
also increased in dogs with ADHAC compared to the
normal dogs. Hyperfibrinogenemia was common in
these dogs with ADHAC, and is a potential explanation of the elevated MAfibrin. Furthermore, a mild
positive correlation between MAfibrin and fibrinogen
concentration was identified. Hyperfibrinogenemia
increases risk of thromboembolic disease in humans,40
although its significance in dogs is not well
defined.8,10,13 In addition, a previous study found
increased CL60 in dogs that were administered prednisone, suggestive of decreased fibrinolysis.30 Decreased
fibrinolysis was not noted when CL30 was measured in
this study, but CL60 was not examined. Further investigations of the role of elevated fibrinogen concentration, fibrin clot strength, and incidence of delayed
fibrinolysis in dogs with hyperadrenocorticism are
warranted in patients suspected to be hypercoagulable,
including dogs with immune-mediated hemolytic
anemia, neoplasia, and protein-losing diseases.
In this study, there was variability noted in MAfibrin
results in both normal and ADHAC dogs, which
1140
Park et al
might limit the use of TEG-PM in dogs. As MAfibrin
contributes to both MAAA and MAADP, when MAfibrin
approaches MAthrombin, it is not possible to assess the
response to AA and ADP with TEG-PM. This might
limit the utility of TEG-PM in dogs in disease states
characterized by hypercoagulability, in which high
MAfibrin values might be seen. It remains unclear
whether the large variability noted in the MAfibrin
results is a typical finding in dogs. Larger studies of
both normal and diseased dogs are recommended to
further characterize TEG-PM variables, especially
MAfibrin, and to determine if this is a suitable method
of analyzing platelet function in dogs.
In this study, PT was significantly shorter in dogs
with ADHAC compared with healthy dogs at all time
points. The clinical relevance of this finding is not
known, as all PT results were still within the previously established institutional canine reference interval.
However, the significantly shorter PT identified in the
ADHAC dogs of this study might be another marker
of hypercoagulability and warrants future study.
Subnormal PT results are not commonly found in
dogs with thromboembolic disease,2,5,13,41 or dogs
with thromboelastographic evidence of hypercoagulability.9,14,42
Despite the high prevalence of proteinuria, decreased
plasma AT activity was not documented in any of the
dogs with ADHAC; thus, AT deficiency does not
appear to be a reason for the observed hypercoagulability. Previously, significantly lower AT activity in
dogs with hyperadrenocorticism was reported in comparison with healthy dogs.43 In contrast, the mean AT
activity in the dogs with hyperadrenocorticism was
100%. Dogs with AT activity <60–80% of normal are
thought to be at increased risk of hypercoagulability;
therefore, it is unlikely that the AT activity of dogs in
this study contributed to the observed hypercoagulability.44,45 However, a limitation of this study is that AT
and UPCR were not measured in all dogs at all time
points.
Another limitation of this study is that the normal
population used to generate TEG-PM reference intervals was not age-matched to the ADHAC population
to act as a true control group. Human TEG tracings
become more hypercoagulable with aging, and might
be partly attributable to a decline in hematocrit with
increasing age.46,47 To the author’s knowledge, the
effect of age on canine TEG results has not been evaluated and further investigation is warranted. However,
in this study, the hematocrit was not significantly
different in the ADHAC dogs compared with the
healthy dogs.
Hypertension was frequently found in this population of dogs with ADHAC. In agreement with
previous studies, blood pressure did not decrease significantly despite resolution of hypercortisolemia.48,49
Hypertension in dogs with PDH might cause endothelial dysfunction, via increased shear stress on small
blood vessels and increased expression of procoagulant factors such as platelet-activating factor. This
could lead to activation of the coagulation cascade
and increased risk of thrombus formation. However,
stress might have influenced the blood pressure readings in this study,50 which were all taken in the hospital environment, and the blood pressure of the
healthy dogs was not measured for comparison.
Nonetheless, further investigation into the role of
endothelial dysfunction in the pathogenesis of thromboembolic disease in patients with ADHAC is
warranted.
The LDDST and ACTH stimulation test have a limited specificity of approximately 80%, presenting a further limitation to this study, especially in light of the
majority of dogs having normally sized adrenal glands
on ultrasound.1 No dogs in this study had apparent
nonadrenal illness to account for their clinical signs. In
addition, the vast majority of dogs with normally sized
adrenal glands on ultrasound had adrenal gland width
measurements at the upper end of the reference range.
There is a recognized overlap in the adrenal gland sizes
of normal and ADHAC dogs.1,24,k However, there is a
potential for false-positive diagnoses of ADHAC in
this study.
In conclusion, dogs with naturally occurring
ADHAC have evidence of hypercoagulability with
several citrated kaolin TEG and TEG-PM variables
significantly different from those of normal dogs, indicating a more rapid rate of clot formation and
increased clot strength. PT was significantly shorter in
the dogs with untreated ADHAC and hyperfibrinogenemia was common. AT activity in the ADHAC dogs
was not significantly decreased despite the majority of
dogs having significant proteinuria. Approximately,
half of the dogs with untreated ADHAC were hypertensive. The majority of the hemostatic abnormalities
identified in this study persisted in the dogs treated for
ADHAC despite normalization of cortisol concentration. Further prospective studies are needed to evaluate the risk of thromboembolic disease in dogs with
ADHAC and hemostatic abnormalities.
Footnotes
a
Vetoryl; Vetoquinol, Lavaltrie, QC
Acthar repository corticotropin injection 40 U/mL; Questcor
Pharmaceuticals, Union City, CA
c
BD Vacutainer, Franklin Lakes, NJ
d
Model 811-B; Parks Medical Electronics Inc, Las Vegas, NV
e
Amelung KC4; Trinity Biotech, Jamestown, NY
f
Haemoscope Corporation, Niles, IL
g
ACL Elite; Beckman Coulter, Danvers, MA/HemosIL Coagulation Systems antithrombin assay, Werfen Group, Lexington,
MA
h
Siemens Multistix 10SG, Tarrytown, NY
i
SAS, version 9.1.3; SAS Institute Inc, Cary, NC
j
Kol A, Nelson RW, Borjesson DL. Dogs with hyperadrenocorticism are hypergoagulable and have prolonged PFA-100 closure times. Proceedings of the 60th and 44th Annual Meetings
of the American College of Veterinary Pathologists and the
American Society for Veterinary Clinical Pathology; 2009
December 5–9; Monterey, CA
b
ACTH-Dependent Hyperadrenocorticism
k
De Marco V, Pereira RS, Kage NK. Ultrasonographic adrenal
glands thickness measurement in dogs with pituitary-dependent
hyperadrenocorticism in comparison with normal dogs matched
by weight body. Proceedings of the 28th American College of
Veterinary Internal Medicine Annual Conference; 2010 June
9–12; Anaheim, CA
Acknowledgments
The investigators acknowledge the Ontario Veterinary College Pet Trust Fund for funding this study. In
addition, the investigators thank Vetoquinol Canada
and Dechra Veterinary Products, UK for supplying
the trilostane used in this study.
Funding: This study was supported by a grant from
the Ontario Veterinary College Pet Trust Fund.
Conflict of Interest Declaration: One author (SLB)
has received funding from Vetoquinol Canada for
speaking fees and preparation of educational materials
in the last 3 years.
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