Higher Threshold for VTE Test Cuts Unnecessary Imaging

Pam Harrison

October 13, 2014

TAMPA, Florida — The negative predictive value of the D-dimer test is just as good when the threshold for venous thromboembolism (VTE) is raised, new research shows. And in a sizeable proportion of patients, the higher threshold can eliminate the need for costly and invasive radiologic testing.

When the upper limit of the reference value on the D-dimer test is raised from 230 ng/mL to 500 ng/mL, the sensitivity and negative predictive value of the test remain unchanged, at 100%, said presenter Ahmed Abdulrahman, MD, pathology resident at the Drexel University College of Medicine in Philadelphia.

Most important, 16% of radiologic testing that would have been required at the lower reference value could be eliminated at the higher value, resulting in a cost saving to the hospital of approximately $250,000 over an 8-month period, he explained here at the American Society for Clinical Pathology 2014.

"We did this study to see how many patients fall into the category above 230 ng/mL, which is above the normal reference range in almost all the labs. We found that a lot of patients were undergoing extra radiologic testing, only to find that the vast majority of them were negative for VTE," Dr Abdulrahman told Medscape Medical News.

In fact, raising the reference value to 500 ng/mL does not affect the negative predictive value of the test, meaning that no patients with VTE will be missed, yet a lot of unnecessary testing can be eliminated," he explained.

The study involved patients who presented to the emergency department of the Hahnemann University Hospital in Philadelphia with chest pain, shortness of breath, or both. The first cohort, comprised of 239 patients, presented from December 2012 to February 2013; the second cohort, comprised of 417 patients, presented from January to May 2014.

All patients underwent D-dimer testing and were assessed with the Wells clinical decision tool. The Wells tool uses clinical history and physical examination to stratify patients by risk for pulmonary embolism.

All patients were followed to determine outcome and whether further imaging was performed.

In the two cohorts, different D-dimer categories were used to stratify patients.

Table. D-Dimer Values in the Two Cohorts

D-Dimer Value (ng/mL) Stratification by D-Dimer Value, n Subsequent Radiologic Testing, n
Cohort 1    
   <230 174 18
   230–500 37 19
   ≥500 28 22
Cohort 2    
   <500 356 66
   ≥500 61 55

 

In the first cohort, "of all 59 patients who had imaging done, only 3 had radiologic evidence of pulmonary embolism," Dr Abdulrahman reports. And all 59 had D-dimer values above 500 ng/mL and had an intermediate pretest probability of having pulmonary embolism on the basis of risk stratification score.

In the second cohort, "of all 121 patients who had imaging done, only 10 had radiologic evidence of pulmonary embolism, and all of them had D-dimer values above 500 ng/mL," the investigators report. Pretest probability of pulmonary embolism was intermediate to high in this group.

The hospital now uses the higher reference value for D-dimer tests to refer patients with suspected VTE for additional radiographic tests.

"Hopefully, our emergency physicians are doing a good job triaging these patients and targeting only those who really need further testing, so it will be more cost-effective," Dr Abdulrahman said. "At the same time, we'll be able to decrease the time patients spend undergoing extra testing and the radiation burden they would get from additional testing."

Reducing Pointless Testing

There has been a perspective that the best way to save money in laboratory testing is to not order tests, said Joseph Mark Tuthill, MD, division head of pathology informatics at the Henry Ford Health System in Detroit.

"Clearly, there is no value in ordering the same test every day over and over again, but we've been pretty good at stamping that out," he told Medscape Medical News. What people don't appreciate is the value of ordering the right test at the right time, he said.

"Interestingly, very expensive tests may seem to be a waste of money, but if you order one very expensive test and it saves thousands of dollars down the line, you've actually saved a lot of money by eliminating a lot of ancillary problems ahead of time," he noted.

For example, many blood clotting disorders could set a patient up for deep vein thrombosis, which could trigger a stroke. If you could diagnose that patient with a $1000 test and implement therapy to prevent a stroke, "you've saved $50,000 on a patient who is now admitted as an acute thromboembolic problem, not to mention all of the chronic downstream effects of that patient having had a stroke," Dr Tuthill explained.

"One of the most important things a laboratory needs to do is to help guide physicians in their decision-making around ordering the right laboratory test, although this is very difficult to do," he added.

Dr Abdulrahman and Dr Tuthill have disclosed no relevant financial relationships.

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