Report from ARRS: Studies identify expanded role for D-dimer test

Reports of the demise of the D-dimer test for suspected pulmonary embolism may be greatly exaggerated, according to two new studies. Multislice CT angiography has become the de facto standard for pulmonary embolism detection, but researchers in Illinois and Hawaii have shown the inexpensive blood test can effectively rule out PE in patients with low and even intermediate risk while eliminating unnecessary CTA exams.

With the swift rise of pulmonary CTA as the preferred test for PE, D-dimer assays are now used mainly for risk stratification and clinical decision making. Though physicians still rely on D-dimer for ruling out PE in patients with a low clinical probability of disease, the test's sensitivity for other risk groups has been questioned, said Dr. Rajan T. Gupta, a radiologist at the Advocate Illinois Masonic Medical Center in Chicago.

Gupta and colleagues at Advocate and at the Rosalind Franklin University of Medicine and Science in North Chicago prospectively enrolled 501 consecutive patients who presented to the emergency room from April 2007 to January 2008 with clinically suspected PE. Patients underwent PE screening with three different methods:

• revised Geneva score (RGS), an algorithm used to classify patients as having a low, intermediate, or high clinical probability of PE

• quantitative immunoturbidimetric D-dimer with a standard cutoff value of 1.2 mg/L

• pulmonary CTA

The investigators found that the D-dimer assay could accurately rule out PE not only in patients with a low clinical probability, but also in those with an intermediate probability of having the condition. They also found that if the D-dimer had been used as a first-line test in these two groups, about one in four CTAs could have been avoided. They presented their results at the 2008 American Roengten Ray Society meeting in Washington, DC.

Using the RGS algorithm, researchers classified 229 and 258 patients, respectively, as having a low and an intermediate clinical probability of PE. Fourteen patients were classified as having a high probability under the same protocol. CTA diagnosed 23 patients with PE. No patients with D-dimer values below 1.2 mg/L had PE on pulmonary CTA in the low or intermediate clinical probability groups. Only one patient was diagnosed with acute PE with a D-dimer less than 1.2 mg/L. This patient suffered from systemic lupus and was categorized as high clinical probability based on the RGS.

In another study, researchers at Honolulu's Kaiser Foundation Hospital and John A. Burns School of Medicine at the University of Hawaii prospectively assessed the utility of the D-dimer test on 347 patients presenting to the ER with suspected PE.

All patients had a D-dimer below 1 µg/mL and underwent pulmonary CTA. ER physicians assessed PE's clinical probability using the Wells clinical prediction score. All CTAs were interpreted a second time by a radiologist blinded to CTA and D-dimer results. The researchers compared ER and radiological interpretations and had a second radiologist interpret discrepant readings. They found that only 10 patients had a high clinical probability of PE.

According to coauthor and presenter Travis Ing, only one patient with a D-dimer value below 1 µg/mL and a Wells score of 0 had a positive CTA, suggesting that the Wells clinical assessment criteria may be moot in patients with low serum D-dimer values.

"In patients with a low serum D-dimer level, a pulmonary CTA study positive for acute embolism, especially if located in a distal segmental or subsegmental artery, should be viewed with caution," Ing said.

For more information from the Diagnostic Imaging archives:

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Study builds argument for CCT triple rule-out to screen chest pain patients in ER

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Imaging raises more questions in acute pulmonary embolism