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Antithrombin (AT) Aspergillus spp. Serology 1309

Antithrombin (AT)
VetBooks.ir Definition Next Diagnostic Steps to Consider Lab Artifacts

Endogenous anticoagulant. Major plasma if Levels Are High • Age: Lower levels of AT have been reported
inhibitor of serine protease factors of the Increased plasma AT concentration is not in young animals.
coagulation cascade (factors IX, X, XI, XII; clinically significant. • Assay differences: AT may be overestimated
thrombin and plasmin). in certain thrombin chromogenic assays
Causes of Abnormally Low Levels (heparin cofactor II activity in addition to
Synonyms Increased loss (e.g., protein-losing nephropathy, AT is detected).
Antithrombin III (outdated), heparin cofactor protein-losing enteropathy), increased hepatic
clearance of AT enzyme complexes (e.g., dis- Specimen Collection and Handling
Physiology seminated intravascular coagulation [DIC], Citrate (blue top tube), separate plasma (within
Synthesized in liver; AT binds to thrombin, sepsis), decreased production (e.g., liver failure) 1 hour of sample collection) and transfer to
preventing conversion of fibrinogen to fibrin; plastic tube; freeze (store at 0°C-4°C). The
heparin and heparin-like compounds acceler- Next Diagnostic Steps to Consider citrate tube must be filled completely, as the
ate the reaction between AT and thrombin. if Levels Are Low ratio of blood to citrate is important for accurate
AT inactivates several additional coagulation Assess other aspects of the coagulation cascade testing.
factors as well. Decreased AT (due to loss or (activated partial thromboplastin time and pro-
consumption) can result in a hypercoagulable thrombin time), platelet count, fibrinogen level, Relative Cost: $$
state and increased risk of thrombosis. D-dimers, fibrin degradation products and, if
available, thromboelastography. A procoagulant Pearls
Reference Interval state may exist because of low AT levels alone or Patients with DIC, thrombosis, or nephrotic
Measured as a percentage of species-specific in conjunction with other disorders (e.g., DIC). syndrome commonly have decreased levels. If
pooled samples. Dogs: 75%-120%; cats: the AT activity is <70% of the control, the
75%-110%. Drug Effects animal may require anticoagulation using drugs
Plasma AT is decreased in dogs with hyper- other than heparin.
Causes of Abnormally High Levels adrenocorticism (hyperadrenocorticism can
Exogenous glucocorticoid administration (dogs), be associated with thromboembolic disease). AUTHOR: Deborah G. Davis, DVM, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
inflammation (as part of positive acute-phase L-asparaginase can decrease AT production.
response in cats)

Laboratory Tests
Aspergillus spp. Serology

Definition specific) than for sinonasal infection (≈24% Relative Cost: $$$
Specific tests may detect either antibodies sensitive).
to Aspergillus spp. (by ELISA, agarose gel Pearls
immunodiffusion [AGID], or counter immu- Causes of Abnormally High Levels • False-positive and false-negative results
noelectrophoresis) or the presence of Aspergillus • Antibody tests: presence of antibodies can occur with all tests for aspergillosis
galactomannan antigen (GMA) (ELISA) in the indicates exposure, but not necessarily active (including culture, cytologic analysis, and
serum or urine. infection. histopathologic analysis).
• Antigen: presence of serum or urine antigen • Penicillium spp. is another genus of fungus
Physiology indicates systemic infection, colonization, or that can cause nasal disease in dogs. The
• Aspergillus spp. are common environmental may be a false-positive. organisms appear similar and can only be
fungi (saprophytes) and opportunistic patho- differentiated via culture or serologic testing,
gens (dogs >> cats). Sinonasal aspergillosis Important Interspecies Differences not cytologic appearance. Serologic tests
(A. fumigatus) is far more common than Serologic tests often use species-specific antibod- that detect antibody to either antigen are
disseminated aspergillosis (A. terreus, A. ies; confirm that test used is valid for the species preferred.
flavus, others) (p. 81). in question. • Both Penicillium spp. and Aspergillus spp.
• Nasal imaging showing turbinate destruction are ubiquitous in the environment.
and areas of radiolucency in coordination Lab Artifacts • Aspergillus GMA ELISA in serum or urine is
with rhinoscopy for direct visualization of False-positive results for the GMA ELISA are more sensitive in detecting systemic disease
fungal plaques and to obtain specimens seen in dogs given Plasmalyte crystalloid fluids than localized nasal or pulmonary disease,
for analysis (cytologic, histopathologic, or or some Penicillium-derived antibiotics. and false-positive results are seen in dogs
microbiological) are the most informative with other systemic fungal diseases.
tests for sinonasal infection, but AGID is Specimen Collection and Handling
sometimes useful. Serum, 1 mL (red top tube); stable at 2°-8°C AUTHOR: Sharon M. Dial, DVM, PhD, DACVP
• GMA ELISA is more useful for systemic for five days; freeze at 20°C for longer storage. EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
aspergillosis (≈85%-90% sensitive and

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