Page 2363 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 142 Venous Thromboembolism 2105

phlegmasia cerulea dolens, which is severe leg pain with swelling, can reliably detect thrombi, most such reports have not used venog-
cyanosis, venous gangrene, compartment syndrome, and arterial raphy as their reference standard. Furthermore, whether the value
compromise. Patients with phlegmasia cerulea dolens may experience of this test is maintained when it moves from highly specialized
circulatory collapse and shock, which may result in death or loss of vascular laboratories into community ultrasonography laboratories is
the affected limb. unknown. A potential limitation of venous ultrasonography is its
inability to visualize the iliac veins and the segment of the superficial
femoral vein within the femoral canal. This is not a serious limitation
Differential Diagnosis because isolated thrombi within the femoral canal or the iliac vein
are rare. Furthermore, the obstruction produced by iliac vein thrombi
The differential diagnosis of patients with suspected DVT includes often limits the compressibility of the common femoral vein segment
musculoskeletal disorders (muscle or tendon strains or tears), lym- and hence will be detected indirectly. Doppler color flow can also be
phatic obstruction, venous insufficiency, a ruptured popliteal (Baker) used to assess for blood flow and occlusion within a vein. The
cyst, cellulitis, sciatica, muscle hematoma, and postthrombotic combination of compression ultrasonography and Doppler is often
syndrome. referred to as duplex ultrasonography.

OBJECTIVE DIAGNOSTIC TESTS FOR DEEP D-Dimer Assays
VENOUS THROMBOSIS
D-dimer assays use mono- or polyspecific antibodies against D-dimer
Both invasive and noninvasive tests are useful for the diagnosis of to provide quantitative or qualitative data on the concentration of
DVT. Venography is the only invasive test of proven value, and D-dimer in whole blood or plasma. D-dimer is the product of lysis
venous compression ultrasonography is the most widely studied and of cross-linked fibrin and the levels of D-dimer are increased in
used noninvasive test. Although other imaging modalities have been patients with acute VTE. However, the test is nonspecific because the
studied (e.g., magnetic resonance direct thrombus imaging), these are level of D-dimer can be increased in a variety of other conditions,
not commonly performed. including malignancy, inflammatory conditions, and infections.
Therefore the D-dimer assay is most useful as a tool to rule out
suspected DVT.
Venography D-dimer assays have two principal limitations: (1) a positive test
result is nonspecific and should not be used as the sole criterion
Venography remains the reference standard for the diagnosis of DVT, for diagnosis of VTE, and (2) numerous test kits are available that
although it is rarely performed because of the availability of reliable have different sensitivities for VTE. Thus D-dimer results are not
noninvasive tests. Venography is technically difficult, and its proper interchangeable between kits. D-dimer assays employ different
execution and interpretation require considerable experience. Venog- standards with some using fibrinogen and others using D-dimer.
raphy may produce superficial phlebitis and can cause DVT, but with This results in differences in reporting because laboratory cut-offs
good technique ascending venography outlines the entire deep venous depend on which standard is used. This has led to confusion among
system of the lower extremities, including the calf and iliac veins. It clinicians regarding the use of D-dimer assays. Further, the use of an
is currently used only when noninvasive testing is not feasible or the insensitive D-dimer assay to rule out VTE could result in omission
results of such testing are inconclusive. of required diagnostic testing, thereby placing patients at risk for PE
and death.
The optimal setting for use of a D-dimer assay is in the assessment
Venous Compression Ultrasonography of patients with a low clinical pretest probability of VTE. The
combination of a low pretest probability (determined using a vali-
Venous ultrasonography is performed using a high-resolution real- dated scoring system) and a negative result with a validated D-dimer
time scanner equipped with a 5-MHz electronically focused linear assay rules out the diagnosis of acute VTE, obviating the need for
array transducer. The common femoral vein and femoral artery are additional testing. Evaluation of the levels of D-dimer may be of value
first located in the groin, with the patient in a supine position. The in patients with suspected recurrent VTE, and it may assist in
femoral vein (a deep vein) is then examined along its course. Next, decision-making about optimal duration of anticoagulation.
the popliteal vein is located and examined down to the level of its
trifurcation into the peroneal and tibial veins. At each of these loca-
tions, the vein being examined is compressed gently but firmly with DIAGNOSTIC STRATEGIES FOR ACUTE DEEP
the transducer probe, and the results are observed on the monitor. VENOUS THROMBOSIS
Hard copies from freeze-frame images of both stages of the procedure
are obtained and serve as a permanent record. Diagnostic algorithms for the noninvasive diagnosis of clinically
In symptomatic patients, venous compression ultrasonography suspected VTE are presented in Fig. 142.1. If compression ultraso-
has a sensitivity and specificity for detection of proximal DVT nography is not immediately available, patients can be empirically
(femoral or popliteal vein) of more than 95%. However, ultra- anticoagulated pending diagnostic testing on the subsequent day.
sonography is less sensitive for detection of calf vein thrombosis. In assessing patients with suspected acute DVT, clinical prediction
Ultrasound examination can be repeated 7 days after the initial study rules assign a clinical pretest probability (high, intermediate, or low
to increase its sensitivity for detection of clinically important calf probability) based on the clinical manifestations and the presence
vein thrombosis and to improve the safety of diagnostic strategies or absence of risk factors. The Wells clinical prediction rule for
that do not include venography in patients with suspected calf vein DVT assigns a risk category based on the following factors: active
thrombosis. This strategy will detect the 10%–30% of calf vein cancer (or cancer treated within the previous 6 months), calf swelling
thrombi that extend proximally. If the ultrasound examination result ≥3 cm compared to the asymptomatic leg, swelling of superficial
remains negative after 7 days, the risk of clinically important proximal veins (nonvaricose), unilateral pitting edema, tenderness along the
extension is negligible, and it is safe to withhold antithrombotic deep venous system, such as recent immobilization (≥3 days) or
treatment. major surgery (within 12 weeks), and absence of alternative diag-
If the field of examination is extended to the distal popliteal vein nosis. Acute DVT can be excluded in patients with a low clinical
and the proximal deep calf veins, venous ultrasonography detects probability (based on a validated clinical prediction rule such as
approximately 50% of calf vein thrombi in symptomatic patients. the Wells score) and negative D-dimer. Patients with moderate or
Although there are reports that ultrasound examination of the calf high clinical probability should proceed to objective testing. Patients