Deep Vein Thrombosis is important. Clots in the legs can travel to the lungs causing pulmonary embolism and death. In fact pulmonary embolism -abbreviated to PE -is second only to cardiac events as a cause of sudden death. The media seems to regularly report the unexpected death of apparently previously healthy people from PE. The data are also striking: PE is the third commonest cause of death among patients in hospital and 60% of patients who die in hospital have PEs at post mortem examination. During pregnancy and shortly afterwards, PE is the leading cause of maternal mortality and morbidity in this country. But DVT can be very difficult to diagnose.
So how do we investigate patients thought to be at risk, without inundating our ultrasound service? In this short video-blog, I will describe a diagnostic algorithm for DVT.
First Step in Diagnosis of Deep Vein Thrombosis
The most important step in making the diagnosis is thinking of it. For medico-legal reasons, this should always be documented in the differential diagnosis. There are a number of situations, which may alert you to the diagnosis of DVT. The following are common risk factors: hereditary thrombophilias such as Protein C deficiency, Protein S deficiency, Factor V Leiden mutation; Surgical predispositions such as recent major surgery; and acquired medical risks such as previous DVT or PE, malignancy, stroke, immobilisation inflammatory bowel disease, nephrotic syndrome.
The Wells Clinical Model for predicting the likelihood of a DVT is very helpful. Various clinical characteristics are given a score and if the score is less than 2, DVT is unlikely, if the score is 2 or greater the likelihood is described as likely. I will put a link in the description below to the reference, and if you pause the video you can read it in detail.
The diagnostic algorithm based on the Wells score is shown in the video above. Patients in whom a diagnosis of DVT is being considered with a score of less than 2 have a D-dimer blood test. If the D-dimer is not raised – ie negative – the diagnosis of DVT may be safely excluded. Those with a raised D-dimer – ie positive – require an ultrasound scan. If this is negative, the diagnosis of DVT may be safely excluded and of course patients in whom the diagnosis is confirmed require treatment. If the scan is delayed, heparin treatment should be started. In patients with a Wells score of 2 or more, the algorithm is a little more complicated. If the D-dimer is negative and the ultrasound scan is negative, the diagnosis of DVT may be safely excluded. If the D-dimer is positive and the ultrasound scan is negative, many experts suggest that the ultrasound scan should be repeated a week later. The algorithm is shown and you can pause the video to study it.
The first step to diagnosing DVT is to seriously consider it as a possible diagnosis, the second step is to apply the Wells Scoring System in addition to a D-dimer test and then to follow the algorithms that I have presented. In your records, clearly document that you have considered the diagnosis and show that you have followed a recognised protocol.