Page 1420 - Small Animal Internal Medicine, 6th Edition

1392 PART XIII Hematology

TABLE 87.2
VetBooks.ir Interpretation of Hemostasis Screens ACT OSPT* aPTT PLATELETS FIBRINOGEN FDP/D-DIMER

BT
DISORDER
Thrombocytopenia ↑ N N N ↓ N N
Thrombocytopathia ↑ N N N N N N
vWD ↑ N/↑? N N/↑? N N N
Hemophilias N ↑ N ↑ N N N
Rodenticide toxicity N/↑ ↑ ↑↑ ↑ N/↓ N/↓ N/↑
DIC ↑ ↑ ↑ ↑ ↓ N/↓ ↑
Liver disease N/↑ ↑ N/↑ ↑ N/↓ N/↓ N

ACT, Activated coagulation test; aPTT, activated partial thromboplastin time; BT, bleeding time; DIC, disseminated intravascular coagulation;
FDP, fibrin degradation product; N, normal or negative; OSPT, one-stage prothrombin time; vWD, von Willebrand disease; ↑, high or
prolonged; ↓, decreased or shortened; ?, questionable.
*OSPT and aPTT are considered prolonged if they are 25% or more than the concurrent controls.

Unfortunately, the BMBT has high interoperator and intra- TABLE 87.3
operator variability (as high as 80%), and the results are not
reproducible, even by the same operator. The PFA-100 (see Specimens Required for Laboratory Evaluation
later) has largely replaced the BMBT in most veterinary of Hemostasis
teaching hospitals.
By performing these simple tests after evaluating the clin- TUBE TOP
ical features of the bleeding disorder, the clinician should be SAMPLE COLOR TEST(S)
able to narrow down the number of differential diagnoses. EDTA Purple Platelet count
For example, the blood smear evaluation reveals whether blood
the patient is thrombocytopenic or not. If the patient is Citrated Blue OSPT, aPTT, fibrinogen, AT,
not thrombocytopenic but petechiae and ecchymoses are blood vWF, clotting factor assays,
present, a prolonged bleeding time or PFA-100 closure time D-dimer, TEG, PFA-100
support the existence of a platelet function defect (although Thrombin Blue FDP
this situation is uncommon). A prolonged ACT or aPTT
indicates an abnormality in the intrinsic or common path- aPTT, Activated partial thromboplastin time; AT, antithrombin;
ways, a prolonged OSPT documents a defect in the extrin- EDTA, ethylenediamine tetraacetic acid; FDP, fibrin degradation
sic pathway (i.e., factor VII), and a positive test result for product; OSPT, one-stage prothrombin time; PFA-100, platelet
FDPs or D-dimer supports the presence of primary or function analyzer; TEG, thromboelastograph; vWF, von Willebrand
secondary fibrinolysis. factor assay.
If further confirmation of a presumptive diagnosis is
required, plasma can be submitted to a referral laboratory or A routine coagulation screen (or hemostatic profile)
a specialized coagulation laboratory (see p. 1393). Most usually contains the OSPT, aPTT, platelet count, fibrino-
commercial veterinary diagnostic laboratories routinely gen concentration, and FDP and D-dimer concentration. In
evaluate hemostatic profiles. Samples should be submitted in some laboratories, AT activity may also be included. The
a purple-topped tube (sodium EDTA) for platelet count, a OSPT primarily evaluates the extrinsic pathway, whereas
blue-topped tube (sodium citrate) for coagulation studies the aPTT primarily evaluates the intrinsic pathway. Because
(OSPT, aPTT, fibrinogen concentration, D-dimer), and a the end product in these assays is always fibrin formation,
special blue-topped tube (Thrombo-Wellcotest, Thermo both tests also evaluate the common pathway (see Fig. 87.2).
Fisher Scientific, Lenexa, KS) for FDP determination (the The D-dimer assay evaluates for systemic fibrinolysis, as does
last tube is usually supplied by the diagnostic laboratory). the FDP test; however, as noted, the D-dimer is formed after
The blue-topped tubes are now primarily available in 3.2% fibrin has been stabilized by factor XIII. Thus it is more
sodium citrate concentrations. The results of routine hemo- indicative of intravascular thrombus formation. The inter-
stasis assays are not affected by the concentration of citrate pretation of routine hemostasis profiles is summarized in
used (Morales et al., 2007). It is important to submit the right Table 87.2.
samples in the appropriate anticoagulant. The guidelines for New instruments now allow evaluation of other aspects
sample submission to commercial laboratories are summa- of hemostasis. For example, the platelet function analyzer
rized in Table 87.3. PFA-100 (Siemens Healthcare Diagnostics, Deerfield, IL) is