D-dimer test alone can simplify diagnosis of DVT

2020 10 13 15 16 3485 Blood Test D Dimer 400

A D-dimer blood test may be all that's needed to help healthcare providers determine which patients require additional screening to diagnose deep vein thrombosis (DVT), according to research published October 15 in Blood Advances. This would simplify the diagnosis of DVT without compromising accuracy by only administering one test and not several, including ultrasound.

Current guidelines for diagnosing DVT are complicated, time-consuming, and could be challenging to undertake in busy hospital emergency departments. The guidelines incorporate clinical pretest probability (C-PTP) assessments, D-dimer results, and compression ultrasound (CUS).

The guidelines recommend first undertaking C-PTP, which involves determining whether a patient has the common signs and symptoms of DVT, and then designating them as high or low risk. If the patient is found to be at high risk for DVT, they undergo an ultrasound exam. If not, the patients will have D-dimer screening to determine whether subsequent screening, including ultrasound, is needed.

The new study assessed the safety and feasibility of a diagnostic strategy that rules out DVT in patients with negative D-dimer, and which rules out DVT with normal findings on a single whole-leg compression ultrasound exam for patients with positive D-dimer test results, according to the scientists.

Applying this strategy in their study, the investigators examined 1,397 individuals who were referred to the emergency department of Østfold Hospital in Norway for suspected DVT between February 2015 and November 2018. Positive D-dimer was defined as levels greater than or equal to 0.5 mg/mL fibrinogen-equivalent units. Those who had positive D-dimer blood test results were referred for whole-leg ultrasound scans to further screen for DVT.

Patients with D-dimer of less than 0.5 mg/mL were considered not to have DVT. Patients with negative D-dimer results, or with positive D-dimer results but negative ultrasound results, were discharged without taking C-PTP into account. Of the 1,113 people with normal workup based on the strategy, only six developed DVT in the subsequent three months, suggesting that the D-dimer test may be a feasible first step in diagnosing the condition.

The research team, led by Dr. Synne Fronas of the department of emergency medicine of Østfold Hospital in Gralum, Norway, made note of an important proviso. The study assessed the use of D-dimer tests in only those patients who were referred to the emergency department. These patients were already preselected with suspected DVT. Fronas and colleagues cautioned that D-dimer alone may not be useful for assessing DVT in a general population patient group.

The authors wrote they believed that their strategy was safe.

"We found that our simple approach of performing a single whole-leg [compression ultrasound] only in patients with D-dimer greater than or equal to 0.5 mg/mL and withholding [compression ultrasound] in patients with D-dimer of less than 0.5 mg/mL was a safe strategy associated with a low failure rate," they stated.

Moreover, they indicated that with the failure rate of their strategy at 0.5%, and well within their preaccepted safety margin, they would not suggest undertaking any systematic follow-up of patients with negative D-dimer or negative compression ultrasound. The latter is in line with current guidelines, they noted.

In addition to comparable safety, the researchers reported that their approach has other advantages. They wrote that it may reduce the number of ultrasound exams, in turn decreasing cost, time, and resources needed to manage individual patients.

A second advantage, according to the scientists, involves avoiding the challenges with clinical prediction rules. These include an inherent weakness of subjectivity, not widely validated interrater reliability, and incorrect use.

"The latter may partly result from the fact that, in some emergency departments, standard blood samples, including D-dimer, are obtained before clinical evaluation to improve efficiency. Knowledge of D-dimer results prior to C-PTP assessment may influence scoring, contrary to the intended use," the researchers wrote.

The investigators noted that while the relatively large number of patients is one of their study's strengths, its monocentric design may negatively affect the generalizability of their findings. External validity still must be established. Also, only one D-dimer assay was examined, which could limit extrapolating the findings to other assays, such as point-of-care device assays, the authors stated.

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