The Haematex Newsletter
Hyphen BioMed Update
Hyphen BioMed have released a new Liaphen test for Protein C. This joins the current Liaphen range, which are very simple one step quantitative tests for Fibrinogen, Antithrombin, free Protein S and von Willebrand factor. Hyphen Biomed will have a stand at ISTH in London and would welcome any visits from Aussie haematologists or coag lab scientists.
...on the significance of weak lupus anticoagulant (LAC)
Only recently noticed a potentially important paper on the significance of weak lupus anticoagulant (LAC). According to this publication, patients showing a weakly positive LAC result with the Stago dRVVT Screen/Confirm pair (just over the normal cutoff) have a 7-fold higher risk of thrombosis than those with a normal result. (Clinical relevance of isolated lupus anticoagulant positivity in patients with thrombotic antiphospholipid syndrome. Yin D, de Groot PG, Ninivaggi M, Devreese KMG, de Laat B. Throm.Haemost.2021 121:1220-1227).
This publication is likely to stimulate even greater use of the Stago dRVVT for thrombophilia testing than currently. But there may be a problem? Most of this patient group were already on warfarin when tested (private communication from Bas de Laat).
So, is this a correct conclusion or not? It has been observed in other studies that patients on warfarin tended to have higher Screen/Confirm ratios than untreated patients being screened for LA. One paper (Isert M, et al. Int J Lab Hematol. 2015. 37: 758-65) suggested an increased cutoff of 1.7 for patients on warfarin rather than the usual 1.2-1.3 for normal. So, is this a cause or effect? It’s probably unethical to test normal individuals for LA before and after warfarin but that’s probably what is needed. That, or perhaps mixing tests to reduce the effect of the factor deficiency in warfarin plasmas might be useful after all.
Flip de Groot is an eminent co-author on this paper and is well known for previously publishing that only “triple positive” LA patients (with LAC, anticardiolipin and antibeta2 GPI antibodies) posed significant thrombotic risk. In this latest study with Yin, triple positive LA were less significant for thrombosis than the isolated weak dRVVT results. Interestingly, none of the 30 cases displayed LAC in a LAC sensitive APTT test, nor had anticardiolipin or anti beta2GPI antibodies.
Katrien Devreese, also a co-author on this paper, previously showed the Stago reagents to have 10.8% false positive rate in warfarin plasmas compared with nil with the Haematex dRVT reagent pair. (Depreter B, Devreese KMJ. Dilute Russell's viper venom time reagents in lupus anticoagulant testing: a well-considered choice. Clin Chem Lab Med. 2017. 55:91-101).
Haematex is currently developing an adsorbent similar to DOAC Stop which removes heparin from plasmas without introducing any other effect and invites any lab which may be interested to participate in pioneering studies to contact us by e-mail.
We also have an experimental collagen product, similar to the previous Horm collagen, which might be useful for some labs. We can provide free samples to any lab expressing interest in trying it out for aggregation or surface binding studies.
Happy clotting from Haematex