Computer-assisted strain gauge plethysmography (CaSGP), D-dimer and prospective risk stratification as screening tools for DVT in the Emergency Department.



Rich Greiner, Class of 2004
Box 513

Faculty Advisor

Dr. Christopher DeFlitch, Emergency Medicine

Research Period

June 2001 - September 2003


  1. This study is designed to evaluate CaSGP, D-dimer and clinical risk factors, both independently and collectively, for patients with suspected Deep Vein Thrombosis (DVT) presenting to the Emergency Department (ED).
  2. The goal of this study is a protocol for DVT diagnosis in the ED that will be more cost efficient and timely than the current protocol while limiting the need for duplex ultrasonography.



Deep Vein Thrombosis (DVT) affects approximately 2 million Americans per year and if left untreated can cause fatal Pulmonary Embolism (PE)1. Approximately 1 person in 20 develops DVT over her or his lifetime, and 600,000 hospitalizations for DVT occur annually in the US.2 Suspected DVT is a common diagnosis in ED patients at Hershey Medical Center (HMC), representing up to 40-60 patients per month. The clinical diagnosis of DVT is unreliable and about three-quarters of the patients who present with suspected DVT have other causes of leg pain1. Currently, gold standards for diagnosis of DVT include venography and venous duplex imaging (VDI), which are both costly and not available on a 24-hour basis. Therefore, there is an obvious need for screening tools to reduce the use of these expensive tests that would otherwise be negative in over 75% of patients. A screening tool for DVT must be very sensitive as untreated DVTs can lead to a fatal PE, as previously mentioned.

Recently a large Canadian study proposed a series of 9 questions that would stratify patients into pretest probability (PTP) categories of low, moderate or high. Previous studies have shown that patients with a low PTP had a low prevalence of DVT; however, the low PTP alone was not sensitive enough to be used alone to screen for DVT. Also d-dimer has recently been used as a very sensitive, yet very non-specific, test to screen for DVT and PE. When we first proposed this study in 2001, there were no confirmatory studies published, to my knowledge, of Wells' Pre-test probability (PTP) criteria in the U.S. Since then there have been a few studies evaluating Wells' criteria and some evaluating d-dimer as screening tools for DVT. There had also been no studies, other than by Wells, which I was aware of, using both PTP and d-dimer to screen for DVT in the ED.

The original motivation for this study was to evaluate CaSGP as a screening tool for DVT in the ED. The CaSGP was used and studied in Europe and supposedly had a higher sensitivity and specificity than both PTP and many d-dimer assays. We designed a study that would evaluate all three modalities of CaSGP, PTP and d-dimer as screening tools for DVT in our population. See attached recommended Algorithm for this study. (Encl 1)


Over an 18-month time period, a prospective, convenience sample of adults who met inclusion criteria for the study with attending emergency physician suspected DVT were enrolled. Inclusion criteria included: age 18 or older, symptoms suggestive of DVT, able to lie still for 2 minutes (for CaSGP) and able to give informed consent. Institutional IRB approval was obtained. A formal training protocol was performed for all CaSGP operators to standardize testing. Patients were evaluated by an ED physician and risk stratified into low, moderate or high pre-test probability (PTP) based on Well's criteria. (Encl 2) In addition to ED collected demographics, the physician recorded the clinical risk stratification data, and recorded the results of the d-dimer. The ED technician performed CaSGP and obtained computer generated results.

All patients received venous duplex imaging, VDI, our gold standard for this study, within 12 hours of presentation. The vascular technician performing the VDI was blinded to the results of the 3-phase screening (PTP, d-dimer & CaSCP). Treatment was based on VDI results.

Student's Responsibilities

  1. Develop a plan for the study (including research, study protocol, algorithm, IRB proposal)
  2. Minor administrative duties necessary for study execution
  3. Data gathering, evaluation and presentation
  4. Creating an abstract and poster presentation at conclusion of study to present at American College of Emergency Physicians (ACEP) Scientific Assembly in Boston in October 2003.


Sponsor's Responsibilities

  1. To provide guidance in all phases of study
  2. To ensure that all ED required tasks and training related to the study are addressed and completed
  3. To ensure that all data gathering and evaluation is complete and accurate
  4. To edit and approve final presentations for this study



  1. Anand SS, Wells PS, Hunt D, Brill-Edwards P, Cook D, Ginsberg JS. Does This Patient Have Deep Vein Thrombosis? JAMA 1998; 279:1094-1099.
  2. Schreiber D. Deep Venous Thrombosis and Thrombophlebitis emedicine.com. Jan 14, 2002.
  3. Anderson DR, Wells PS et al. Management of Patients with Suspected DVT in the ED: Combining use of a clinical Dx model with d-dimer testing. Journal of Emergency Medicine. 2000; 19: 225-230.
  4. Escoffre-Barbe M, Oger E et al. Evaluation of a New Rapid D-dimer assay for clinically suspected DVT (Liatest D-Dimer) Am J Clin Pathol. 1998; 109: 748-753.
  5. Shields GP, Turnipseed S, Panacek EA, Melnikoff N, Gosselin R, White RH. Validation of the Canadian Clinical Probability Model for Acute Venous Thrombosis. Acad Emerg Med 2002; 9:561-566.



  1. Recommended suspected DVT evaluation algorithm
  2. PTP risk stratification form


I do give permission for my proposal to possibly be published on the College of Medicine website.

Rich Greiner 

Christopher DeFlitch, M.D.