Featured Post

Is the new professionalism and ACP's new ethics really just about following guidelines?

The Charter ( Medical Professionalism in the New Millennium.A Physician's Charter) did not deal with just the important relationship of ...

Wednesday, January 11, 2006

Still another algorithm for diagnosis of pulmonary embolism

The Jan. 11, 2006 issue of JAMA has an article (The Chistopher Study,vol..295,no.2,172-179) with a proposed system or algorithm for diagnosing pulmonary emboli (PE) using the Wells decision rule, the d-dimer blood test and the CT scan. It works like this: if the Well's score is less than 4 then a negative dimer sufficiently excludes PE so that no further tests are done. If the Wells number is 4 or more then a CT is needed even if the dimer is negative.Less than 4 is said to make PE Unlikely and 4 or more is Likely.
This was a large (3306 consecutive patients) study from 12 centers in Holland. The absence of PE was not determined by pulmonary angiography but the study relied on a nearly complete 3 month followup. An important issue is which d-dimer test was used. This study used a very sensitive immunosorbent assay (Vidas d-dimer).The immunosorbent and immunoturbidimetric tests are very sensitive-said to be greater than 95%- while the latex agglutination assays are less so. Excluding PE on the basis of a "unlikely"Wells score plus a negative d-dimer will only work well if a very sensitive assay is used.
I wonder if the "dichotomized"version of the Wells decision rule is too simple.All patients in the "unlikely" category are not equally unlikely to have PE. I have a problem with reducing a physician's assessment of how likely the diagnosis may be to a mechanistic rule and apparently excluding any and all other elements that a physician may call upon to decide the likelihood of a diagnosis. for example a decreased o2 saturation. A clinician's "global assessment"( i.e. considering the overall clinical picture not just the check list from Wells) should trump the decision rule.If you believe PE or DVT is a reasonable diagnosis to pursue,testing should be done even if the Wells rule suggests low risk or unlikely and the d-dimer is negative.(show me a blood test that can't be wrong)
An editorial in the same issue is written by a well respected DVT/PE expert ,Dr. R.D.Hull from Calgary who is enthusiastic about the Christopher study authors' proposed algorithm. He says in part " ... firm recommendations can now be made concerning practical and fairly simple diagnostic algorithms for evaluating patients with suspected PE or deep vein thrombosis". D-dimer testing and the increasingly technically impressive CT imaging techniques are giving us better tools for the often elusive and vexing problems associated with venous thromboembolism but I have concerns that reliance on decision rules make things seem more simple than they really are and there is much more to clinical judgment than is captured in a simple checklist decision rule.

No comments: