LETTER
Impedance Plethysmography and DVT Diagnosis
H. Brownell Wheeler and
Frederick A. Anderson Jr.
1 August 1993 | Volume 119 Issue 3 | Pages 246-247
TO THE EDITOR:
The retrospective study by Anderson and colleagues [1] focused on venographic correlations in a selected subset of patients as opposed to clinical utility for the entire patient population. Methodologic problems in this study included selection bias for venography, the use of non-filling of veins or venous segments for diagnosis, and reliance on an alternative (and unproven) gold standard [2] when venography was unsatisfactory. Furthermore, the cited European study [3] used different instrumentation and a different method of interpretation than the standard IPG technique. In fact, the authors' data suggest that 90% of their patients could have been managed appropriately by IPG alone. Most patients (63%) had normal IPG results, received no other tests, and did well without treatment, assuming that known adverse outcomes would have been reported. Similar favorable clinical outcomes in untreated patients with normal IPG results are well documented in prospective studies [4, 5]. In addition, of 85 patients with normal IPG results who had venography because of strong clinical suspicion of DVT, 64 had no DVT, and only 2 had DVT of the calf. These patients would have been managed appropriately by IPG alone, as would 37 patients with abnormal IPG results and confirmed thrombi. If all patients had been managed solely by IPG, only 5.2% would have been treated unnecessarily, and 4.9% would have failed to receive customary treatment. Many highly regarded diagnostic tests have a much lower reliability when used as the sole criterion for treatment. This clinical utility could have been improved further by venography or duplex scanning in those patients where the clinical impression and IPG results were at odds. It would be unfortunate if a retrospective review written from a negative perspective deterred use of a test with proven clinical utility in carefully controlled, prospective studies.
1. Anderson DR, Lensing AW, Wells PS, Levine MN, Weitz JI, Hirsh J. Limitations of impedance plethysmography in the diagnosis of clinically suspected deep-vein thrombosis. Ann Intern Med. 1993; 118:25-30.
2. Davidson BL, Elliott CG, Lensing AW. Low accuracy of color Doppler ultrasound in the detection of proximal leg vein thrombosis in asymptomatic high-risk patients. Ann Intern Med. 1992; 117:735-8.
3. Prandoni P, Lensing AW, Buller HR, Carta M, Vigo M, Cogo A. Failure of computerized impedance plethysmography in the diagnostic management of patients with clinically suspected deep-vein thrombosis. Thromb Haemost. 1991; 65:233-6.
4. Huisman MV, Buller HR, ten Cate JW, Vreeken J. Serial impedance plethysmography for suspected deep venous thrombosis in outpatients. The Amsterdam General Practitioner Study. N Engl J Med. 1986; 314:823-8.
5. Hull RD, Hirsh J, Carter CJ, Jay RM, Ockelford PA, Buller HR, et al. Diagnostic efficacy of impedance plethysmography for clinically suspected deep-vein thrombosis. A randomized trial. Ann Intern Med. 1985; 102:21-8.
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