In contrast, the initial test of choice for high-risk patients is venous ultrasound. The guideline states that D-dimer may be used to confirm a negative venous ultrasound but should not be used as the initial test. In all risk categories, including high-risk patients, the combination of a negative venous ultrasound and negative D-dimer negates the need for further testing.

The guideline recommendations become more complex if results of the diagnostic testing are contradictory. This predominantly arises in the setting of a positive D-dimer but a negative venous ultrasound. In this case, the venous ultrasound should be repeated in one week. This particular recommendation may be the most challenging to comply with for practitioners in emergency medicine, as follow-up appointments, particularly those involving diagnostic imaging, can be difficult to arrange.

Patients should be given clear discharge instructions recommending the repeat ultrasound, and explaining that while DVT is unlikely, the diagnosis has not been conclusively ruled out.

For any patient in whom pretest risk stratification is not performed, the best initial test is a venous ultrasound. If negative, a concurrent D-dimer test or a follow-up venous ultrasound in one week is indicated.

Some special circumstances bear mention. While DVT most typically occurs in the lower extremities, all of these recommendations remain in effect, without significant modification, whether the DVT is suspected in an upper or lower extremity. Also, pregnant patients require a separate diagnostic algorithm given the complications associated with D-dimer testing. In pregnant patients, if the venous ultrasound and D-dimer are both negative, no further testing or treatment is indicated.

However, most of these patients will have a positive D-dimer, and therefore any negative venous ultrasound in a pregnant patient with a positive D-dimer should be confirmed by repeat venous ultrasound in one week.

While on first reading these recommendations by the American College of Chest Physicians may seem complex, the underlying concept is simple: The greater the pretest probability of DVT, the more thorough the testing must be to exclude the diagnosis. The combination of negative venous ultrasound and negative D-dimer, or negative repeat venous ultrasound one week apart, is considered thorough enough to rule out DVT even in high-risk patients. Keeping this general principle in mind can help physicians in diagnosing and determining disposition of patients from the emergency department.

Reference

1. Bates SM, Jaeschke R, Stevens SM, et al. Diagnosis of DVT: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians evidence-based clinical practice guidelines. Chest. 2012;141:e351S-e418S.