According to the ASH, the evidence-based guidelines "are intended to support patients, clinicians and health care professionals in VTE diagnosis." Specifically, the society's guideline development panel evaluated diagnostic strategies for pulmonary embolism (PE), deep vein thrombosis (DVT) of the lower and upper extremities, and recurrent VTE.
"Determining whether a patient has VTE is a common clinical problem we face in primary care, and these guidelines provide an evidence-based strategy to efficiently evaluate patients for VTE," said AAFP Commission on Health of the Public and Science member James Stevermer, M.D., of Fulton, Mo.
Pulmonary embolism (PE): First, for patient populations with low prevalence/pretest probability (i.e., 5% or less), the ASH guidelines recommend that clinicians use a D-dimer strategy to rule out PE, followed by a ventilation/perfusion (VQ) lung scan or CT pulmonary angiography (CTPA) in patients who require additional testing. D-dimer testing alone should not be used to diagnose PE, the guidelines note.
Second, for populations with intermediate prevalence/pretest probability (i.e., about 20%), the guidelines suggest that clinicians use a D-dimer strategy to rule out PE, followed by VQ scan or CTPA, if indicated.
For these two populations, using an age-adjusted D-dimer cutoff in outpatients older than 50 is as safe as using the standard cutoff and improves diagnostic yield, the guidelines note. Age-adjusted cutoff = age (years) x 10 µg/L (using D-dimer assays with a cutoff of 500 µg/L).
Finally, in populations with a high prevalence/pretest probability (i.e., 50% or more), the guidelines suggest that clinicians start with CTPA when assessing patients suspected of having PE. If CTPA is not available, a VQ scan may be used, with appropriate followup testing.
"D-dimer testing alone should not be used to diagnose PE and should not be used as a subsequent test after CT scan in patients with a high pretest probability/prevalence," the guidelines note.
The ASH guidelines also suggest a strategy that starts with D-dimer to exclude recurrent PE in a population with unlikely pretest probability. For patients who have a positive D-dimer or likely pretest probability, followup CTPA should be performed.
Lower-extremity Deep Vein Thrombosis (DVT): Next, for patient populations with low prevalence/pretest probability (i.e., 10% or less), the guidelines recommend that clinicians use a D-dimer strategy to rule out DVT, followed by proximal lower-extremity ultrasound or whole-leg ultrasound in patients who require further testing.
In these patients, positive D-dimer alone should not be used to diagnose DVT, and additional testing after negative proximal or whole-leg ultrasound should not be conducted.
For populations with intermediate prevalence/pretest probability (i.e., about 25%), the guidelines suggest using whole-leg ultrasound or starting with proximal lower-extremity ultrasound to assess patients with suspected DVT. Serial proximal ultrasound testing is needed after a negative proximal ultrasound. No further testing is needed after a negative whole-leg ultrasound.
For patients with suspected DVT and high prevalence/pretest probability (i.e., 50% or more), a strategy that starts with whole-leg ultrasound or proximal lower-extremity ultrasound is suggested. Serial ultrasound should be used if initial ultrasound is negative and no alternative diagnosis is identified.
The guidelines suggest using a strategy that starts with D-dimer to exclude recurrent DVT in a population with unlikely prevalence/pretest probability.
Upper-extremity DVT: Lastly, for patients with low prevalence/unlikely pretest probability, D-dimer testing is suggested to exclude upper-extremity DVT, followed by duplex ultrasound if positive, the guidelines say.
For patients with high prevalence/likely pretest probability, either D-dimer testing followed by duplex ultrasound/serial duplex ultrasound, or duplex ultrasound/serial duplex ultrasound alone can be used to assess patients suspected of having upper-extremity DVT.
Again, a positive D-dimer alone should not be used to diagnose upper-extremity DVT.
The guidelines' recommendations hinge on proper stratification of patients into low, intermediate or high probability of having VTE, Stevermer told AAFP News.
"There are some widely validated rules (Wells score for PE and DVT and the Geneva score for PE) that can help stratify patients' risk," he said. "Based on the pretest probability, the guidelines make recommendations for the use of D-dimer and other testing."
Stevermer acknowledged that the guidelines offered some surprises.
"The differential strategy for patients at intermediate risk (ultrasound as first step for lower-extremity DVT, and a D-dimer as the first strategy for PE) was new to me," he said. "I also think using age-adjusted D-dimer to evaluate people for a PE can safely reduce unneeded testing, especially in the elder population."
Previously, the AAFP had endorsed a 2007 guideline on VTE diagnosis by the American College of Physicians (ACP), Stevermer said, but the ACP sunset the guideline with no plans to update it.
"When we found out the ACP guideline was being sunset, we looked for other guidelines to potentially replace it," he said. "Fortunately, ASH uses a transparent and evidence-based methodology (similar to the AAFP's) to develop its clinical guidelines, so we were able to endorse their guidelines in place of the older guideline."
Stevermer said that although ASH's guidelines are fairly long (which helps provide transparency), the clinical recommendations are easy to identify, and useful clinical guidance is given with each step.
"I'm hoping more clinical societies implement the rigorous guideline development policy that led to this clinical policy," he said in closing.