Let me preface this by saying I work with both the IAC and Radiology
standards and my own lab scans from thigh to ankle. Medical staff, not
administrators (or anyone with a stop watch), should determine how medical
testing gets performed.
But not everyone who scans to the knee (and not below it) is jeopardizing
patients or even doing a bad job.
BTW, the AIUM-ACR standard DOES recommend scanning below the knee
when the study does not explain the patient's symptoms, e.g. calf pain with a
negative femoropopliteal study.
"Symptomatic areas such as the calf generally require additional evaluation
and additional images if the cause of the symptoms is not readily elucidated
by the standard examination."
"The patient presentation, clinical indication, or clinical management pathways
may require protocol adjustments such as more detailed evaluation of the
superficial venous system, evaluation of the deep calf veins, or a bilateral
While it is true that many DVT are totally or in part below the knee, there are
reasonable people who think scanning below the knee is NOT necessary for all
Many centers, especially Europeans and North American internal medicine
groups, use 2 thigh to knee ultrasounds a week apart. This requires two scans
for moderate to high risk groups and no further scanning for low risk groups
or those with negative d-dimer (I recognize how few patients get good
evaluation before coming to a lab and this is one reason while I personally
support the complete examination). This approach is well researched and is
The current anticoagulation guidelines from the Chest Physicians support this.
The chapters are hundreds of pages long and have a VERY long chapter on
diagnosing DVT. The guidelines do not recommend treating everyone with calf
DVT and support tailoring imaging to diagnose treatable conditions rather than
all DVT (i.e. calf DVT)
How did they come to this conclusion.
1) Very few people evaluated have DVT, they have something else.
2) The minority of patients with calf DVT will propagate to above the knee
3) Larger veins are more likely to cause symptomatic PE, calf veins not at all
or only rarely.
4) There is weak evidence that treating calf DVT affects the rate of chronic
venous insufficiency or recurrent DVT. (Obviously more work needs to be done
since it makes some sense that treating a disease earlier should help).
5) The risks of anticoagulation are real and the risks of overtreating
insignificant calf DVT may outweigh the benefit of treating calf DVTs which
have a more aggressive natural history.
1. Guyatt GH, Akl EA, Crowther M, Gutterman DD, Schuunemann HJ, for
the American College of Chest Physicians Antithrombotic Therapy and
Prevention of Thrombosis Panel. Executive Summary: Antithrombotic Therapy
and Prevention of Thrombosis, 9th ed: American College of Chest Physicians
Evidence-Based Clinical Practice Guidelines. Chest. 2012Feb.6;141(2
2. Bates SM, Jaeschke R, Stevens SM, Goodacre S, Wells PS, Stevenson
MD, et al. Diagnosis of DVT: Antithrombotic Therapy and Prevention of
Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based
Clinical Practice Guidelines. Chest. 2012Feb.6;141(2 suppl):e351S–e418S.
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