Diagnosing deep vein thrombosis - time for a cost-effective approach?
EDITOR-The paper on the diagnosis, investigation, and management of
deep vein thrombosis by Tovey and Wyatt 1 quite rightly highlighted the
fact that clinical diagnosis of DVT is unreliable. DVT is a valid
surrogate for pulmonary embolism(PE). Therefore some form of imaging is
necessary. Develpoment of non-invasive imaging systems in recent years
have largely obviated the need for invasive testing. A recent study has
major implications for practice because it showed that combination of low
pre-test probability (PTP), and a negative D-dimer test safely excluded
DVT and PE, obviating further investigation in 47% of patients. 2 However,
the occurrence of DVT in upto 20% of patients with a high PTP and a
negative D-dimer test emphasises the point that D-dimer testing can not be
used in isolation. 2
I agree with Tovey and Wyatt that D-dimer tests have a high negative
predictive value (NPV) and can reduce the need for imaging when used in
conjunction with PTP, and plethysmography or ultrasonography. 1 It is not
acceptable to miss a DVT in any patient. The NPV of any test or
combination of tests must approach 100%.
Tovey and Wyatt have discussed the different test kits for D-dimer,
including the near patient SimpliRED test which has been widely validated
in controlled studies. In a recent study, however, SimpliRED D-dimer assay
showed a sensitivity of only 63.4% in the diagnosis of DVT at an emergency
department. 3 As the quality of routine D-dimer testing is improving, we
can hope that a ‘best test’ for D-dimer may soon emerge.
Recently another study had showen that the inter-rater variability of
both Wells and the Geneva scores were not affected by the experience of
the assessing clinician 4, bearing in mind that majority of patients will
be managed initially by the most junior doctors in an emergency setting.
Wells score relies heavily on the clinician judgement regarding whether a
diagnosis is as or more likely than a DVT or a PE. Its complexity renders
it difficult to apply in practice. In contrast, the Geneva scoring system
is simple and is completely standardized. 4
I agree with Tovey and Wyatt about the role of plethysmography in the
diagnosis of DVT which is cheap, and reliable, and can be performed by a
trained staff in an emergency department. I suggest that the Bayesian
approach of combining the plethysmography with PTP scoring and a modern D-
dimer may be an ideal choice for a district general hospital (DGH) in
order to reduce the cost of investigations for DVT, without jeopardising
the safety of patients. In this manner, we can approach a NPV of 100% for
eliminating DVT, fulfilling the general assumtion of good practice. It has
been shown that it is possible to exclude DVT safely by using
plethysmography, in combination with PTP and D-dimer assay and can be the
most cost-effective approach at a DGH and should now be the initial
diagnostic step. 5 However, randomised controlled studies are necessary
before implementing this practice in every DGH.
1. Tovey C, Wyatt S. Diagnosis, investigation, and management of deep
vein thrombosis. BMJ 2003; 326: 1180-84.
2. Wells PS, Anderson DR, Rodger M, et al. Excluding pulmonary
embolism at the bedside without diagnostic imaging: management of patients
with suspected pulmonary embolism presenting to the emergency department
by using a simple clinical model and D-dimer. Ann Intern Med 2001; 135: 98
3. Kilroy DA, Ireland S, Reid P, Goodacre S, Morris F. Emergency
department investigation of deep vein thrombosis. Emerg Med J 2003; 20: 29
4. Iles S, Hodges AM, Darley JR, Frampton C, Epton M, Beckert LEL,
Town GI. Clinical experience and pre-test probability scores in the
diagnosis of pulmonary embolism. Q J Med 2003; 96: 211-15.
5. Sinharay R, Strang G, Bird D. Cost effective strategy for a safe
diagnosis of DVT at a district general hospital. Postgrad Med J 2003; 79:
( in press ).
Competing interests: No competing interests