Test and retest – the key to correct diagnosis of VWD types


14 Apr 2016

Repeat testing is key to reducing errors in the identification of types of von Willebrand disease (VWD), in particular Type 2M, says a leading researcher.

A new study published in Haemophilia particularly highlighted the “considerably greater difficulty” laboratories had in identifying Type 2M VWD.

They correctly identified T2M VWD on average only 29.4% of occasions, with a significant 70.6% error rate.

Lead author Emmanuel J Favaloro, Principal Hospital Scientist at Westmead Hospital’s Institute of Clinical Pathology and Medical Research, said it was important for specialists to be aware of how commonly VWD is misdiagnosed or missed.

“This is due to a combination of factors,” he told the limbic.

“Clinicians, haematologists and others that may be involved in the management of patients, rely heavily on the results of testing of patient blood. There are a number of steps in this process, beginning from the blood draw, the sample processing (centrifugation to obtain plasma; storage of blood/plasma prior to testing), then the tests are performed, and the results relayed to the doctor, often with some sort of laboratory based ‘interpretation’ around the likelihood of VWD, and the type of VWD.”

VWD is the most common inherited bleeding disorder and is characterised by low levels of and/or abnormal function in the plasma protein von Willebrand factor (VWF). Mr Favaloro said the study findings were significant.

“Any misdiagnosis is significant,” he said. “Our ongoing recommendation to clinicians is to always repeat a test in a given patient to mitigate any diagnosis problem. That way a misdiagnosis can generally be avoided.”

The study also questions the representation that Type 2A VMD is the most common of the Type 2 sub-types, and suggests it might be more about a case of mistaken identity.

“Most labs do not identify Type 2M VWD – they identify these cases (usually) as Type 2A,” Mr Favaloro explained. “Thus, many clinicians do not even know that Type 2M VWD exists – the labs may suggest it is 2A VWD, and that is the diagnosis the patient receives.

“Type 2M VWD is generally considered a rare VWD type; however, it is my contention that this is just a case of mistaken identity. Data from my lab and a few select labs worldwide who actually recognise 2M VWD cases properly, suggest it is just as common as 2A VWD.”

The clinical significance of this is difficult to estimate, although was currently perhaps not high as patients are treated similarly whether they have 2A or 2M.

However, he said it was likely to become important in the future.

“I cannot say it currently strongly impacts patient treatments and efficacy, but I do predict it will in the future – so, now is a good time to redress the problem and educate people,” he said.

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