Left Rule, D-Dimer Measurement and Complete Ultrasonography to Rule Out Deep Vein Thrombosis During Pregnancy.

In pregnant women with suspected DVT, a sure diagnosis is mandatory. Indeed, false positive tests lead to inappropriate anticoagulant treatment, which increases the risk of bleeding. Conversely, false negative tests might lead to a life-threatening thromboembolic event. Thus, accuracy of diagnostic methods used in pregnant women is crucial [1].

In non-pregnant patients, sequential diagnostic strategies based on 1) the assessment of clinical probability, 2) D-dimer measurement and 3) compression ultrasonography (CUS) have been widely validated [2, 3].

Clinical probability assessment by clinical prediction rules (CPRs) is a crucial step in the management of suspected DVT. However, the most commonly used CPR for DVT, the Wells' score, has never been validated in pregnant women [3]. Recently, the 'LEFt' clinical prediction rule was derived and internally validated by Chan et al. among 194 pregnant women investigated for suspected DVT[4]. This rule combines three variables: symptoms in the left leg ("L"), calf circumference difference equal or greater than 2 centimeters ("E" for edema) and first trimester presentation ("Ft") [4].

We performed an external validation of this rule on a recently published prospective cohort of pregnant patients with suspected DVT (submitted to JTH). This external validation showed that a negative "LEFt" rule accurately identified pregnant women in whom the proportion of confirmed DVT appears to be very low. A prospective validation of this rule is now warranted, and we plan to use it in our prospective study.

The second step used in the diagnostic strategy including non-pregnant patients is D-dimer measurement. The test has been widely validated in non-pregnant patients and, in association with a non-high clinical probability, it allows to safely rule out DVT [5].

As D-dimer level raise steadily during pregnancy, the specificity of the test decreases and it is less useful in pregnant women. A recent study suggested that the currently available sensitive D-dimer assays that are used for the exclusion in symptomatic non-pregnant women have the potential to exclude DVT in symptomatic pregnant women with the application of higher cut-points [6]. Even if this data arises from a small study, it clearly suggests that the usual cut-off set a 500 ng/ml would safely rule out DVT in pregnant women [6]. As the usual cut-off has never been prospectively validated in pregnant women with suspected DVT, we would like, as a first step, to use it in our study.

In pregnant patients, limited data is available on the use of complete compression ultrasonography to rule out DVT. In a recent prospective management study, we included 226 pregnant and post-partum women with suspected lower limb DVT. We observed a 1.1% (95% CI:0.3-4.0) three-month thromboembolic event rate in those left untreated on the basis of a negative single complete CUS [7]. This result is in line with what was reported after a normal phlebography, the gold standard test [8].

Even if complete CUS is safe to rule out DVT in pregnant women, current diagnostic strategies for suspected DVT in non-pregnant patients rely on the use of clinical probability and D-Dimer prior to leg veins imaging [5]. However, no management outcome study on the safety and usefulness of D-Dimer to rule out DVT in pregnant women is available to date. Another limitation of the strategies based on a single unique complete CUS, is that every woman has to undergo complete CUS. However, this test is not always available. Therefore, a strategy in which the association of clinical probability assessment and D-dimer measurement would allow to safely rule out DVT in a significant proportion of patients without performing a complete CUS, would be of great help in everyday clinical practice and would probably be cost-effective.

Therefore, we plan a prospective study to assess the safety of a sequential diagnostic strategy based on the assessment of clinical probability with the LEFt rule, D-dimer measurement and complete CUS in pregnant women with suspected DVT.