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Dilemma: D-dimer testing

You hear another practice is doing near patient testing for D-dimers to rule out DVTs. Should you invest in the testing kits out of your own income to generate a new patient pathway?

Dr Asim Malik: D-dimer testing in primary care empowers GPs

Dr Asim Malik - online

DVT can be clinically very difficult to diagnose but early recognition and appropriate treatment can improve clinical outcomes.

The rationale behind the use of D-dimer testing in a primary care setting is to speed up patient assessment. This enables clinicians to determine which patients should be urgently referred for hospital intervention.

It also aims to give optimum care in terms of patient experience by offering care closer to home and assisting signposting to other services where appropriate.

The widespread use of D-dimer testing within primary care offers the opportunity to empower GPs, improve the patient experience by offering faster diagnosis and care closer to home. This will positively impact on productivity by removing unnecessary steps, or delays, in the diagnostic process.

We have been using point of care testing with Wells scoring as a triage tool in primary care since 2007-2008. In our service, patients presenting with a suspicion of DVT are clinically assessed using the Wells scoring tool and a point of care D-dimer test. If the Wells score indicates that patients are low risk and the D-dimer test is negative, then a Doppler scan will not be necessary. An alternative diagnosis will need to be considered.

Several different types of D-dimer kits both qualitative (Clearview) and quantitative (Roche Cobas h232) are available. Both are validated and giving 100% negative predictive values, and can be used by practices with minimal training.

I would strongly encourage practices and CCGs to invest in this project as this can reduce hospital referrals safely and also improve patient experience.

Dr Asim Malik is a GP in Bletchley and at GPSI in cardiology at the Milton Keynes Community Cardiovascular Service.

Dr Ivan Bennett: Better availability will lower the threshold for testing and increase the false positive rate

Dr Ivan Benett - online

Like BNP testing, a D-dimer is rarely useful in general practice, so I would not suggest investing in this product.

A DVT can be ruled out in a patient who is judged clinically unlikely to have DVT and who has a negative D-dimer test.

However, having easy availability will lower the threshold for testing and increase the false positive rate, which is about 50% in a low risk population.

There are many well known risk factors that should alert us to the possibility of DVT. The Wells score allows us to establish the likelihood of DVT based on medical history and clinical examination. A score of zero or less, in other words when there is alternative diagnosis, makes the risk low (<3%). Higher scores increase the risk progressively and a negative test does not reduce the likelihood sufficiently to remove the need for definitive testing by venous ultrasound or venogram.

In general practice, if a patient has more than one clinical feature without an alternative explanation, they need definitive testing. There are a few who may have a DVT but who are at low risk and you need more reassurance. For these I suggest sending blood to the local laboratory for D-dimer testing and being available for the result.

There may be a place for D-dimer tests in A&E where the prior probability of DVT is higher.

Dr Ivan Benett is clinical director of Central Manchester CCG, and a cardiology GPSI in Manchester.

Prof David Fitzmaurice: Inappropriate tests will result in overuse of diagnostic services

Prof David Fitzmaurice NTI

 

It is probably inappropriate for individual practices to implement testing in isolation.

While D-dimer testing is useful in diagnosis of venous thromboembolism, it must be included as part of a diagnostic pathway that includes an assessment of clinical probability (usually the Well’s score) prior to testing and as such it is only negative testing which is useful.

Anyone using these tests will need to understand the performance characteristics of the test being used, the difference between qualitative and quantitative test and how the results affect referral for radiological diagnosis.

As such it is probably inappropriate for individual practices to implement testing in isolation. D-dimer testing must therefore be part of a locality based diagnostic pathway that will involve collaboration with radiological and haematological colleagues as a minimum.

Inappropriate tests will result in overuse of diagnostic services, whereas appropriate use will reduce the need for these services and ultimately reduce costs. These issues need therefore to be considered in a wider setting than practice level, and should be integrated within commissioning decisions within a specific locality.

Professor David Fitzmaurice is a GP and clinical lead for Primary Care Clinical Sciences and deputy head of School for Health and Population Sciences at the University of Birmingham. His main area of research interest is cardiovascular disease.

Readers' comments (1)

  • There are so many confounders to the DDIMER that the answer, at the moment is - no. Until the specificity of the DDIMER - taking into account principally - age and suitable adjustment (see recent papers on this) - then DVT is a Dx based on clinical probability (Wells Score) and scan. Anything else, particularly in an older population, you might as well organise a bus for the elderly to the USS dept on the back of point of contact DDIMERs.

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