From Tom Exner, Haematek: Hope you had a good 4th of July…
Thanks very much for including me sometimes in your interesting online discussions. This time I have an issue on which I would appreciate your advice and possible comments from others if you think it might be suitable for your online interest group.
Regarding significance of weak dRVVT LA test results.
The dRVVT test is favoured by many labs as being simple and reliable for LA. Most labs seem to find 10–20% of “LA positive” results with this test (using current reagent suppliers) in a hospital patient setting based just on “Screen/Confirm” or “LA-1/LA-2″ ratios. This is a much higher incidence than I used to find when I was working at a lab bench. Many such cases display only weak LA and are often on warfarin or other anticoagulants at the time of testing. The combination of thrombotic episode plus LA leads to a diagnosis of anti-phospholipid syndrome according to current classification guidelines.
I would like to know if these weaker LA are “true” LA or if they have been induced somehow by the effect of anticoagulant treatment on the dRVVT. Of course DOACs are well known to mimic LA with the most popular dRVVT reagents, (but not with some newer ones). I’m mainly concerned about the effect of vitamin K antagonists (VKA).
How many such patients with weaker LA whilst on VKA still show abnormal dRVVT Screen/Confirm ratios indicative of LA when the VKA is discontinued or when the INR normalizes. (Note that INR and “Confirm” results are also affected by VK deficiency, and not just VKA).
I would be grateful for any case reports of patients losing their weak LA status and consequently ADS diagnosis when taken off AVK.