17 June 2019

Bringing some clarity to the grey zones of DVT

Clinical General practice

Deep vein thrombosis is hardly a rare phenomenon in general practice. And with most people with the condition only requiring oral therapy, it’s fast becoming GP bread and butter.

However there are still a lot of issues related to the diagnosis and management of DVTs that remain in the grey zone of understanding. When is it worthwhile ordering a D-dimer test? Who should be screened for a thrombophilia? How long should a patient remain on anti-coagulation?

These are just some of the questions a team of eminent Australian researchers, led by neurologist Professor Graeme Hankey from the University of Western Australia and haematologist, Dr Paul Kruger from the Fiona Stanley Hospital in Perth sought to answer in the latest issue of the MJA.

They analysed through all the latest evidence to determine the most appropriate means of diagnosing and managing DVT.

Interestingly, even in our increasingly technological workplace, the initial triage of a patient with a possible DVT involves a clinical assessment. Using the Wells rule to ascertain whether a person is “likely” or “unlikely” to have a clot is still the best initial approach.

Clinical signs alone are rarely sufficient to make the diagnosis as the symptoms of DVT are common to many conditions, and, at the other end of the spectrum, some DVTs are asymptomatic.

If, according to the Wells rule, a DVT is considered likely the patient should be sent straight to ultrasound. If a DVT is deemed unlikely then the researchers suggest you order a D-dimer test.

While a D-dimer level is almost always raised with a DVT, it can also be raised in a number of other scenarios so it’s real value lies in it being negative. If the D-dimer level is normal you can generally rule out a DVT.

A patient with a raised D-dimer level will still need to have a DVT confirmed on ultrasound because of the high false-positive rate.

So once a DVT has been diagnosed, the next most important clinical decision is determining whether it is provoked or unprovoked, as this will have important implications for future investigations, duration of treatment and longer term prognosis, the researchers said.

“Unprovoked [venous thromboembolism] requires assessment for occult cancer, present in up to 10% of patients,” the researchers said. But they stopped short of recommending extensive screening with full body CT scanning or tumour markers, leaving clinicians to decide for themselves the most appropriate investigation based on the clinical symptoms and signs.

As for investigating for thrombophilia, the researchers say the evidence suggests this should not be routine but should be restricted to those patients with an unprovoked VTE who are aged less than 50, have a strong family history of VTE or who have  a history of recurrent thrombosis.

The authors of this update do offer an interesting insight with regard thrombophilias.

“Selecting who to test requires consideration because the results will not change management in most patients with VTE, as the most common thrombophilias (factor V Leiden and prothrombin gene mutations) are not strong predictors of recurrent VTE.”

And as for management, not surprisingly anticoagulation remains the mainstay of treatment. Currently, clinicians have three options for treating the patient with VTE. These include using a DOAC, starting with parenteral therapy followed by a DOAC, or going down the traditional route of parenteral therapy transitioned to warfarin.

Clinicians just need to make a decision with consideration of a number of different factors ranging from medical issues such as renal function and safety to practical issues such as availability and patient preference. Realistically, DOACs are the treatment of choice unless there is a good reason not to choose this option, such as the patient is pregnant.

Duration of anticoagulation depends on whether the clot was provoked or unprovoked. When there is a major transient risk factor that explains the clot, six weeks of anticoagulation is recommended.

When there is a proximal DVT provoked by surgery or trauma, a proximal DVT provoked by a non-surgical transient risk factor or an unprovoked distal DVT, researchers say the evidence recommends three months of anticoagulation.

If the patient has an unprovoked proximal DVT, they need a minimum of three months of anticoagulation, and if they have an active cancer they need at least six months of the anti-clotting therapy.

“Extended anti-coagulation is recommended for a second or unprovoked DVT, if risk factors like active cancer persist, or for unprovoked proximal DVT when the bleeding risk is low,” they said.

Treatments such as an inferior vena cava filter, catheter-directed thrombolysis or surgical removal of the thrombus are very rarely indicated, especially among patients presenting with DVT in the general practice setting.

On the other hand, current evidence suggests compression stockings should always be considered in the treatment of DVT.

MJA doi:10.5694/mja2.50201