Non-invasive detection of deep venous thrombosis: ultrasonography versus duplex scanning

Two cases of jugular vein thrombosis in severely burned patients

Here we present two cases of jugular vein thrombosis in burn patients, with diagnosis, risk factor analysis, and treatment approaches. Severely burned patients have high risk of deep vein thrombosis occurrence due to multiple surgeries. The deep vein catheter should be carefully performed. Once deep vein thrombosis is detected, a wide ultrasonography helps to find other thrombosis sites. During the acute phase, low molecular weight heparin can be used. Upon long-term anti-thrombosis treatment, combined use of herbal medicine during rehabilitation is helpful.

Evaluation of Nucleic Acid Amplification Tests in the Absence of a Perfect Gold-Standard Test

During the past 10 years, medical diagnostic testing for sexually transmitted infections (STIs) has changed markedly as a result of the rapid expansion and marketing of nucleic acid amplification tests (NAATs). Among such new DNA/RNA-amplification techniques are the polymerase chain reaction (PCR), the ligase chain reaction (LCR), and the transcription-mediated amplification (TMA) tests. Regrettably, the test evaluation process undergone by these tests has not always been rigorous or scientifically sound. Here, we review the controversy surrounding the statistical evaluation of these NAATs. We also review some of the traditional and recent statistical methods developed to estimate test sensitivity and specificity parameters in the absence of reliable gold-standard tests. In particular, we review the traditional latent class modeling approach that requires the assumption of independence between diagnostic tests conditional on the true disease status, and the more recent procedures that relax the conditional independence assumption. Finally, we apply some of these statistical modeling techniques to real data to estimate the sensitivity and specificity of a NAAT for Chlamydia trachomatis. On the basis of the latent class modeling approach with a pessimistic prior for culture sensitivity, the NAAT specificity estimate was 97.6% and, on the basis of an optimistic prior, the specificity was 95.3%. Similarly, the sensitivity estimates ranged from 88.1% to 89.6%.

Utility of portable continuous-wave Doppler examination in screening for postoperative deep vein thrombosis

BACKGROUND

Early and accurate diagnosis of post-surgical deep vein thrombosis (DVT) can be difficult and time-consuming, even with duplex ultrasonography. Portable continuous-wave Doppler ultrasonography may be useful in screening patients for postoperative DVT. Further confirmation of Doppler-positive cases by duplex ultrasound might then be more cost-effective.

METHODS

All major post-surgical patients from the departments of general surgery, orthopaedic surgery and colorectal surgery were screened on the third postoperative day for DVT by assessing the quality of the flow signal ("whoosh") obtained by placing the probe over the femoral vein and subsequently over the popliteal vein, both with a distal squeeze, as well as assessment of phasic flow with respiration. An absent or attenuated "whoosh" was judged to be suspicious for DVT and required formal duplex ultrasonography. The first 800 consecutive patients were studied to determine the sensitivity, specificity and accuracy of portable Doppler ultrasonography for DVT screening.

RESULTS

Twenty-four cases of DVT were diagnosed, comprising seven cases in the proximal veins and 17 cases in the calf veins. The sensitivity of Doppler ultrasonography was 12.5% and the specificity was 96.8%. The positive and negative predictive values were 10.7% and 97.3%, respectively.

CONCLUSIONS

Portable Doppler ultrasonography does not have adequate accuracy to be used as a quick screening tool for DVT.

A survey of deep venous thrombosis management by consultant vascular surgeons in the United Kingdom and Ireland

OBJECTIVES

The aim of this study was to detail the current consensus amongst vascular surgeons in Great Britain and Ireland regarding their investigation and management of patients with suspected or proven deep vein thrombosis (DVT).

METHODS

The database of the Vascular Surgical Society of Great Britain and Ireland (VSS) was utilised to send coded postal questionnaires to all consultant surgeon members.

RESULTS

Replies were received from 281 (65%) consultants. Duplex ultrasound is used alone to confirm DVT by 69% of respondents. A thrombophilia screen is always performed by 14% of consultants, for patients with proven DVT, and is more commonly requested by consultants based in a teaching hospital. The majority (57%) of consultants treat DVT with unfractionated heparin (UFH) and warfarin, whereas only 38% utilise low molecular weight heparins (LMWH) and warfarin. A management policy for DVT is reported to be in place by 59%, and a set policy for the specific management of calf vein DVT by just 20%.

CONCLUSION

New diagnostic modalities and treatments have been developed for DVT that are more convenient and cost-effective. Although clinical guidelines for the management of patients with DVT are beginning to emerge, there is still a wide discrepancy in many areas of DVT management, and practice at variance with the current evidence base, amongst vascular surgeons in the United Kingdom and Ireland.

Bias in discrepant analysis: when two wrongs don't make a right

Imperfect reference standards (alloyed standards) often hinder evaluation of new diagnostic tests. Discrepant analysis, a two-stage modification of the standard evaluation of diagnostic tests, has been used to circumvent this problem. In discrepant analysis, additional testing is performed to resolve discrepant results of the new diagnostic test and the alloyed standard. This article demonstrates algebraically that sensitivity and specificity will be overestimated by discrepant analysis, even when a perfect gold standard is used to resolve the discrepant results. The magnitude of the bias depends on the true sensitivity and specificity of the new test and initial alloyed standard, the prevalence of disease in the study population, and the proportion of concordant errors between the two tests. The article also demonstrates substantial bias associated with the use of alloyed standard tests in both stages of discrepant analysis. This procedure should not be used routinely for evaluation of diagnostic tests.

Diagnosis of acute lower limb deep venous thrombosis with ultrasound: trends and controversies

Acute deep venous thrombosis of the lower limb is a common and threatening condition whose clinical diagnosis is known to be unreliable. Sonography has gradually superseded venography as the primary diagnostic procedure. A review of the medical literature shows that sonography offers a high level of sensitivity and specificity in symptomatic patients but suffers from a lack of sensitivity at the calf level and in asymptomatic patients. Technologic progress, as well as increased operator experience, may improve sensitivity. Nevertheless, several critical issues remain unresolved, such as the significance of free-floating thrombi, the usefulness of calf and bilateral examination, the criteria that are essential to the diagnosis, the risk of compression sonography, and sonography's role in the direct detection of venous emboli.

Duplex scanning in the postoperative surveillance of patients undergoing total hip arthroplasty

Color flow duplex imaging is a well-established method for the diagnosis of deep vein thrombosis in symptomatic patients; however, the sensitivity and specificity of duplex scanning compared with venography in high-risk asymptomatic patients are not known. Consecutive patients undergoing total hip arthroplasty who consented to have bilateral venography on days 8 to 12 were included in this prospective study. One hundred and fifty-one venograms were finally obtained in 78 patients. All duplex scanning was performed with the Ultramark 9 ATL (Advanced Technology Laboratories) by one investigator. In the beginning of the study, the first 44 legs, only the femoropopliteal segment was tested and the result was based on B-mode compression; the sensitivity for the duplex was 56% (5/9), and the specificity, 94% (33/35). In the next 107 legs, the addition of color to our criteria improved the sensitivity of the duplex scan from 55% to 93% (13/14) for the femoropopliteal segment and the specificity from 94% to 99% (92/93). For the calf segment, in the same 107 legs, using the color facility of the duplex, the sensitivity and specificity were 79% (15/19) and 97% (85/88), respectively. The color facility of new-generation machines makes duplex scanning reliable for the detection of proximal deep vein thrombosis, even in asymptomatic high-risk patients. For the detection of calf deep vein thrombosis, however, more experience is needed. A larger study is necessary to confirm these preliminary data.