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A National Survey of Practice Patterns in the Noninvasive Diagnosis of Deep Venous Thrombosis

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A National Survey of Practice Patterns in the Noninvasive Diagnosis of Deep Venous Thrombosis
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   Venous thromboembolism, manifested as deep venous thrombosis (DVT) or pulmonary emboliza-tion, is a significant clinical problem. Acute DVT isresponsible for more than 600,000 hospitalizationseach year and a 1-year mortality rate of 21%. 1-4 Because of its accuracy and noninvasive characteris-tics, duplex ultrasound scanning has become thediagnostic test of choice for the detection of DVT. Although venography historically was performedonly on the symptomatic leg, ultrasound scan exam-inations routinely have been performed on both legsbecause of easy patient acceptance and the finding  A national survey of practice patterns inthe noninvasive diagnosis of deep venousthrombosis  John Blebea, MD, Todd K. Kihara, MD, Marsha M. Neumyer, RVT, Judy S.Blebea, MD, Karla M. Anderson, MD, and Robert G. Atnip, MD, Hershey, Pa  Purpose:  Recent studies have recommended unilateral venous duplex scanning for thediagnosis of deep venous thrombosis (DVT) in patients who are unilaterally sympto-matic. Vascular laboratory accreditation standards, however, imply that bilateral leg scanning should be performed. We examined whether actual practice patterns haveevolved toward limited unilateral scanning in such patients. Methods:   A questionnaire was mailed to all 808 vascular laboratories in the United Statesthat were accredited by the Intersocietal Commission for the Accreditation of VascularLaboratories (ICAVL). To encourage candid responses, the questionnaires were numer-ically coded and confidentiality was assured. Results:   A total of 608 questionnaires (75%) were completed and returned. Most of therespondents (442; 73%) were either community-hospital or office-based laboratories, andthe remaining 163 (27%) were university or affiliated-hospital laboratories. Most of thelaboratories (460; 76%) had been in existence for 9 years or more, and 65% had beenICAVL–accredited in venous studies for 3 years or more. Board-certified vascular surgeons were the medical directors in 54% of the laboratories. Duplex ultrasound scanning was thediagnostic method used by 98% of the laboratories. In patients with unilateral symptoms,75% of the laboratories did not routinely scan both legs for DVT. A large majority (75%)believe that bilateral scanning is not clinically indicated. Only 57 laboratories (14%)recalled having patients return with a DVT in the previously unscanned leg, with 93% of these laboratories reporting between one and five such patients. This observation corre-lated with larger volumes of venous studies performed by those laboratories ( P  < .05).Similarly, only 52 laboratories (12%) recalled having patients return with subsequent pul-monary emboli. Of these laboratories, only five reported proximal DVT in the previously unscanned legs of such patients. Of all these laboratories, therefore, only 1% (5 of 443)have potentially missed the diagnosis of a DVT that caused a preventable pulmonary embolus with such a policy. Among those laboratories that always perform bilateral exam-inations, 41% do so because of habit. Most (61%) of the laboratories that perform bilater-al scanning would do unilateral scanning if it were specifically approved by ICAVL. Conclusion:  Three quarters of the ICAVL–accredited vascular laboratories perform lim-ited single-extremity scanning for the diagnosis of DVT in patients with unilateral symp-toms. This broad clinical experience suggests that this practice is widespread in selectedpatients. Clinical protocols should be established to provide guidelines for local labora-tory implementation. (J Vasc Surg 1999;29:799-806.)799 From the Departments of Surgery and Radiology (Dr Judy Blebea), Pennsylvania State University College of Medicine.The opinions contained are the views of the authors and not thoseof any organizations in which they may be members or officers.Presented at the Twenty-second Annual Meeting of theMidwestern Vascular Surgical Society, Dearborn, Mich, Sep25–26, 1998.Reprint requests: Dr John Blebea, Section of Vascular Surgery,Penn State College of Medicine, PO Box 850, Hershey, PA 17033-0850.Copyright © 1999 by the Society for Vascular Surgery andInternational Society for Cardiovascular Surgery, North American Chapter.0741-5214/99/$8.00 + 0 24/6/97865  that there was a high incidence rate of unsuspectedthrombi in the contralateral limb. 3,5,6 More recently,however, studies have shown that contralateralthrombi were rarely of any clinical significance. 7-9 Ithas been proposed that, in patients with unilateralsymptoms, only the symptomatic extremity shouldinitially undergo examination. 7-10 This study wasperformed to investigate the actual practice patternsin the noninvasive diagnosis of DVT in the UnitedStates in regards to bilateral versus unilateral duplexscanning. MATERIALS AND METHODS  A one-page, multiple-choice questionnaire(Appendix) was mailed on December 15, 1997, toall the vascular laboratories that were accredited by the Intersocietal Commission for the Accreditationof Vascular Laboratories (ICAVL). The question-naires were numbered sequentially to ascertain thoseresponding and to assure confidentiality. A follow-up request was sent to the nonresponders at 2 weeksand again at 1 month after the initial mailing. Theanswers to the questions were compiled and ana-lyzed in a blinded fashion. Some responders did notprovide an answer to all the questions.The responses on the completed questionnaires were entered into a relational database (Approach 3.0,Lotus Corp, Boston, Mass). The data subsequently  were analyzed with Excel 95 software (Microsoft,Redmond, Wash). The data are expressed as the mean±the standard error of the mean. Statistical analysis was performed with the SigmaStat statistical program(Jandel Scientific, San Rafael, Calif). The Mann- Whitney test or the t  test were used for continuousdata, and the Fisher exact test or the χ 2 test were usedfor dichotomous data. A P   value of less than .05 wasconsidered to be statistically significant. RESULTS Of the 822 laboratories that were accredited by the ICAVL at the time of the study, 808 were withinthe United States, six were located in Puerto Rico,and eight were in Canada. Of those in the UnitedStates, 608 (75%) returned a completed question-naire. These laboratories form the basis of this report.The geographic distribution was nearly evenly divid-ed between the south, the midwest, and the eastregions of the country (Table I). The most respons-es were from Pennsylvania (53; 9%), New York (44;7%), Ohio (40; 7%), and California (38; 6%). Thisregional and state distribution mirrored the distribu-tion of accredited laboratories reflecting a representa-tive response to the questionnaire. Most of therespondents [442; 73%] were either community-hos-pital or office-based laboratories and the remaining163 (27%) were university or university-affiliatedteaching hospital laboratories (Table II). Most labo-ratories (460; 76%) had been in existence for 9 yearsor more. A total of 87% of the laboratories had beenICAVL–accredited in venous studies for 1 year ormore, and 65% (376 of 577) had been accredited for3 years or more.Most of the laboratories were busy, with 54%(321 of 594) performing more than 2000 total year-ly vascular examinations and only 19% (116) per-forming less than 1000 studies. The number of examinations performed specifically for the diagno-sis of acute lower extremity DVT exceeded 500 casesper year for 57% of the laboratories (334 of 590), while 18% performed less than 250 studies each year.Of these studies, 20% or less were performed as anemergency after-hours procedure in 87% (500 of 576) of the laboratories. Duplex ultrasound scan-ning was the predominant method (98%; 582 of 593) that was used for the noninvasive diagnosis of DVT. Board-certified vascular surgeons were themedical directors in more than half of the laborato-ries surveyed (Table III). Almost half of the labora-tories (49%; 289 of 589) had only one or two full-time vascular technologists employed, and 16% hadfive or more.In patients who were symptomatic with unilater-al leg symptoms, 75% of vascular laboratories (443of 590) did not routinely scan both legs for DVT.Laboratories that performed unilateral scans werelarger, with 32% (139 of 431) having four or more JOURNAL OF VASCULAR SURGERY  800 Blebea et al  May 1999 Table I. Geographic distribution of responses RegionNo. of responses (%) South177 (29%)Midwest173 (29%)East164 (27%) West90 (15%)Unidentified4 (<1%)TOTAL608 Table II. Laboratory location LocationNo. of responses (%) Community hospital 262 (43%)Private office180 (30%)University-affiliated teaching hospital95 (16%)University hospital68 (11%)Mobile laboratory3 (<1%)   vascular technologists as compared with only 21%(33 of 158) among those performing bilateral scan-ning ( P  < .01). Associated with this observation, thelaboratories that always performed bilateral scans dida lesser total number of vascular examinations, with27% (42 of 158) performing less than 1000 per year.Only 17% (74 of 436) of unilateral scanning labora-tories did such a low number of examinations ( P  =.01). There were no significant differences betweenthe laboratories that performed bilateral or unilater-al studies when examined in terms of the region of the country (Table I), the location of the laboratory (Table II), the specialty of the medical director, orthe number of years that the laboratory had been inexistence or had had ICAVL accreditation in venousstudies.Most of the laboratories (68%; 292 of 429) thatperformed unilateral scanning did so more than half of the time (Table IV). The decision for unilateralexamination was made most frequently by the refer-ring physician (Table V). More than half of the lab-oratories (59%; 254 of 428) had a written protocolor criteria for patient selection in determining whichones should undergo unilateral scanning. The prin-cipal reasons quoted for unilateral scanning were abelief that bilateral scanning was not clinically indi-cated (75%; 315 of 420)—that it was more costeffective (14%; 59)—or for research purposes (11%).Three quarters of these laboratories have performedunilateral scanning for more than 5 years (74%; 306of 416).Only 14% of the laboratories (57 of 394) recalledhaving any patient return with an acute proximalDVT in the previously asymptomatic unscanned leg within 1 month of the unilateral examination. Mostof these laboratories (93%; 53 of 59) reportedbetween one and five such patients. The subsequentdetection of contralateral DVT correlated with larg-er volumes of venous studies performed by thoselaboratories ( P  < .05). Similarly, 15% of the labora-tories (52 of 362) recalled having patients return with subsequent pulmonary emboli (PE) within 1month of the unilateral duplex scanning of the lowerextremity. Of these laboratories, only five reported aproximal DVT in the previously unscanned con-tralateral limb of such patients. Of all the laborato-ries that performed unilateral scanning, therefore,only 1% (5 of 443) have potentially missed the diag-nosis of a DVT that may have been associated with apreventable PE with such a policy.Of the 25% of the laboratories (147 of 590) thatalways performed bilateral examinations in patients who were symptomatic with only unilateral legsymptoms, 41% did so because they have alwaysdone it that way, 57% believe that it is dangerous toonly scan one side, 6% fear litigation, and 3% do sofor research purposes. Most of the laboratories(61%) that currently perform bilateral lower extrem-ity venous scanning would perform unilateral scan-ning if specifically approved by ICAVL. DISCUSSION To prevent thrombus extension and pulmonary embolization, early and accurate diagnosis of DVT isnecessary for the timely initiation of anticoagulationtherapy. Signs and symptoms suggestive of DVT areinadequate, and, even when highly suspected, DVTis confirmed only 25% of the time. 11  Venous duplexscanning combines the advantages of a totally non-invasive, relatively inexpensive method with a sensi-tivity of up to 93% and a specificity of 98% in thediagnosis of DVT. 5,12 Clinician acceptance of thisdiagnostic technique has been so encompassing thatit has been questioned whether the threshold forduplex scanning use has been lowered too farbecause so few of the examinations confirm the pres-ence of DVT. 13 Before the availability of ultrasound scan imag-ing, venography had only been performed on thesymptomatic leg because of its invasiveness and thedevelopment of subsequent phlebitis in a small num-ber of patients. Examinations limited to the sympto-matic limb during that time period do not appear tohave been associated with clinically inadequate treat-ment of patients with venous thrombosis. The intro-duction of noninvasive ultrasound scan methodolo-gy allowed both legs to be scanned without any additional risks to the patient. This also provided theopportunity to compare the findings on one side with the contralateral limb. Such routine bilateralexaminations uncovered a high incidence rate of contralateral DVT, even in limbs that were com-pletely asymptomatic, that ranged from 17% to32%. 3,5,6,11 During this same time period, the wide-spread acceptance of noninvasive vascular diagnostic JOURNAL OF VASCULAR SURGERY  Volume 29, Number 5 Blebea et al  801 Table III. Laboratory medical director SpecialtiesNo. of responses (%)  Vascular surgeon336 (54%)Radiologist130 (21%)Surgeon84 (13%)Internal medicine/cardiology48 (8%)Neurologist18 (3%)Other9 (1%)TOTAL625  studies and associated proliferation of vascular labo-ratories led to the formation of the ICAVL. With theobjectives of encouraging and documenting compe-tency in vascular studies, ICAVL accreditation wassought by many laboratories. The requirements foraccreditation in venous duplex ultrasound scanningdefined a complete study as one that included bothlower extremities. 14 The high prevalence of bilater-ality in lower extremity DVT, in association withaccreditation requirements, contributed to the per-ception that bilateral venous scanning should beroutinely performed. 12,6,12 The initial studies that documented a high inci-dence rate of bilateral DVT, however, did not sepa-rately examine the subgroup of patients who weresymptomatic nor define the acuity of the unsuspectedcontralateral DVT in individual patients to determine whether such findings would have affected patientmanagement. Because anticoagulation therapy is sys-temic, the contralateral DVT would be treated just aseffectively as the identified thrombus. To examine theclinical relevance of the contralateral limb in patients who were unilaterally symptomatic, we previously reported on our experience with 2530 patients. 7,9  Although we found bilateral DVT in 28% of thesepatients, no patient with a normal symptomatic sidehad contralateral proximal acute DVT. ContralateralDVT occurred only in the presence of an abnormali-ty in the symptomatic leg. Therefore, no patient would have been denied appropriate clinical treat-ment if only unilateral venous scanning would havebeen done. In addition, we found that a unilateralultrasound scan study decreased the total scanningtime by 21% and had the potential of increasing reim-bursement by approximately 9%. 7  We concluded thatunilateral scanning should be the technique of choicein patients who were symptomatic. Several other stud-ies, which total 1709 patients, also support this view-point that clinical patient management would not bedeleteriously affected if unilateral studies were per-formed in these circumstances. 8,10,15,16  With an overall 75% response rate that was even-ly distributed from all regions of the country and alltypes of vascular laboratories, our survey is fairly rep-resentative of national practice patterns in the UnitedStates today for the ultrasound scan diagnosis of DVT. A large number of university and university-affiliated hospital laboratories responded, but most were community-hospital or office-based laboratories(Table II). Reflecting the qualities necessary to suc-cessfully attain ICAVL accreditation, most laborato-ries have been in existence for 9 years or more. Thelaboratories were fairly busy, with more than half of them performing more than 2000 total vascularstudies each year and more than 500 duplex ultra-sound scans for the diagnosis of DVT. Emphasizingthe extensive nationwide replacement of indirectphysiologic techniques, fully 98% of the laboratoriesused duplex scanning as the method of choice inDVT diagnosis. The results from this survey confirmthat there is widespread implementation of unilateralscanning in patients who are symptomatic in only one leg. Fully 75% of all the surveyed vascular labo-ratories do not routinely examine both legs in this sit-uation. Two thirds perform unilateral scanning morethan half the time (Table IV). Although laboratoriesthat performed unilateral scanning were larger(employing more technologists) and the laboratoriesthat always performed bilateral scanning did a small-er total number of vascular examinations each year,there was otherwise an even distribution across alllaboratory types in the performance of unilateralscanning. There were no differences between univer-sity and community-hospital/private laboratories,regions of the country, specialty of the medical direc-tor, or the number of years that the laboratory hadbeen in existence or had had ICAVL accreditation in venous studies.Consistent with the results from published stud-ies, three quarters of the laboratories that performedunilateral scanning believed that bilateral examina-tions were not clinically indicated and 14% believedthat it was more cost effective to perform unilateralexaminations. Interestingly, most of these laborato-ries have been performing unilateral scanning formore than 5 years. This would antedate all of the JOURNAL OF VASCULAR SURGERY  802 Blebea et al  May 1999 Table V. Decision maker on unilateral scanning Decision makerNo. of responses (%) Referring physician280 (63%) Vascular technologist179 (40%)Medical laboratory director71 (16%)Laboratory physician30 (7%)Combination104 (23%)TOTAL443 Table IV. Frequency of unilateral scanning Proportion of studies No. of responses (%) <25%82 (19%)25% to 50%55 (13%)51% to 75%88 (21%)76% to 99%165 (39%)100%39 (9%)TOTAL429  published studies that recommended such a policy.The survey, however, did not attempt to measure whether there was an increase in frequency with which unilateral scanning has been performed thatmay have been influenced by the published series.Usage patterns also appear to have been affected by referring physicians who were most frequently thedecision makers in determination of a unilateralexamination (Table V). The fact that vascular tech-nologists made the determination on unilateral scan-ning 40% of the time presumably reflects the avail-ability of a written protocol or patient selection cri-teria in 59% of the laboratories.There are inherent and acknowledged limitationsto a survey that is made on the basis of the respon-dents’ memories. Such an instrument cannot accu-rately report on recurrent DVT or PE nor onpatients who are lost to follow-up. Surveys cannotdefine the accuracy of the diagnosis of DVT by indi- vidual laboratories nor their quality assurance pro-grams. Nonetheless, it is worthy to note that only 14% of the laboratories recalled seeing patientsreturn with a contralateral DVT in the unscannedleg. This is well within the range of bilaterality foundin prior published studies. 3,6-9,12,13 The question-naire did not attempt to question the circumstancesof such events and whether they were of any clinicalsignificance. Presumably, however, they were notsignificant because these laboratories would nothave otherwise been expected to continue with aprotocol of unilateral scanning if the medical direc-tor had documented recurrent deleterious out-comes. Along similar lines, 15% of the laboratoriesrecalled having patients return with PE. However,on examination in the vascular laboratory, contralat-eral DVT in the unscanned limbs of these patients was reportedly found in only five of these 52instances for an incidence rate of 10%. It is unknownhow many of these patients also had concomitantsymptomatic side DVT. However, to put thesereports in perspective, of all the 443 laboratories thatperformed unilateral scanning, there was only a 1%incidence rate (5 of 443) of potentially missed DVTthat caused preventable PE. In addition, such anincidence rate, if accurate, is well within the 6%recurrent thromboembolic event rate for patientsundergoing anticoagulation therapy for DVT. 17 Even bilateral scanning is unlikely to prevent allpatients with DVT from having PE. Although thelimitations of such a retrospective survey in this con-text are recognized, these numbers lend support topublished clinical data that show the safety of unilat-eral scanning in selected patients. Among the vascular laboratories that always per-form bilateral venous scanning, 41% continue to doso out of habit and most are not yet convinced of theclinical safety of unilateral examinations. However,61% would perform unilateral scanning if such a pro-tocol were specifically approved by ICAVL. Theaccrediting body does not prohibit such practices andrecognizes that they “may be appropriate for specificindications” and suggests that the laboratory “shouldhave a clinical algorithm” for unilateral examina-tions. 14 They do not, however, elucidate which indi-cations are appropriate nor what algorithm would beacceptable. Almost half of the laboratories describeno written protocols or criteria in place for unilateralscanning. In the laboratories with such documenta-tion, it is unknown how precise they are and from what clinical evidence they are derived. Importantly, we have noted a wide variability in who makes indi- vidual patient examination decisions. There is, there-fore, an obvious need to establish evidence-basedguidelines for local laboratory implementation. Webelieve that it would be beneficial and appropriate forICAVL to support the development of such labora-tory guidelines. In our prior reports, we had madesome suggestions describing which symptomaticpatients would be appropriate for unilateral scanningfor the diagnosis of acute DVT. 7,9 In summary, we have found that three quartersof ICAVL–accredited vascular laboratories performlimited unilateral venous studies in patients who aresymptomatic and have been doing so for a numberof years. Such a broad, under-reported clinical expe-rience suggests that this practice is widespread inselected patients. Clinical protocols should be estab-lished that can provide guidelines for local vascularlaboratory implementation.  We thank Ms Julie Krall for her technical assistanceduring the performance of this survey. REFERENCES 1.Kniffin WD, Baron JA, Barrett J, et al. The epidemiology of diagnosed pulmonary embolism and deep venous thrombosisin the elderly. Arch Intern Med 1994;154:861-6.2.National Institutes of Health Consensus Conference.Prevention of venous thrombosis and pulmonary embolism.JAMA 1986;256:744-9.3.Rubin BG, Reilly JM, Sicard GA, Botney MD. Care of patients with deep venous thrombosis in an academic medicalcenter: limitations and lessons. J Vasc Surg 1994;20:698-704.4.Anderson FA Jr, Wheeler HB, Goldberry RJ, et al. A popula-tion-based perspective of the hospital incidence and case-fatal-ity rates of deep venous thrombosis and pulmonary embolism:the Worcester DVT study. Arch Intern Med 1991;151:933-8. JOURNAL OF VASCULAR SURGERY  Volume 29, Number 5 Blebea et al  803
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