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LA Testing When PTT is Normal?

Hello Geo, I have a question about lupus anticoagulant (LA) testing. Before I go off and tell people wrong I thought I would run this by you. Situation is, we have physicans who want to run antiphospholipid syndrome panels on patients who have a history of having a clot (one time usually).  The activated partial thromboplastin time (PTT) is in normal range as are the prothrombin times (PTs). If they likely had an LA wouldn’t the PTT be prolonged? Is there something I am missing here?
Secondly they are ordering it on patients who are currently on heparin, which is a no no too. Right? Let me know, before I start telling these doctors that the test is not appropriate.  Thanks, Lindsey Davenport-Landry.

Hello, Lindsey, and thank you for your question, which I partially addressed in the last paragraph of my posted response to Mahnaz Sairi on December 5, 2012. The PTT reagent that you use to monitor heparin and to screen for intrinsic and common pathway coagulopathies is probably designed with high phospholipid content so that it is insensitive to LA. This avoids a lot of laboratory follow-up for common, transient, and clinically innocent LAs. Along with several colleagues, I wrote an article on this subject that is referenced in my comments to Mahnaz Sairi, which says in part that the trigger for initiating an antiphospholipid syndrome profile is usually clinical, meaning an unexpected thrombotic event. So your physicians are correct to order the LA profile even though the screening PTT is normal.

You can establish the presence of unfractionated heparin in the LA test specimen using the thrombin time, which will be prolonged, then neutralize up to 1 unit/mL of heparin with an inexpensive commercial polybrene preparation called Hepsorb. Once neutralized, the LA profile works well. If the heparin level exceeds 1 Unit/mL, you would need a new specimen later. I hope this helps! Geo.

Comments (1)
Lupus Anticoagulant
Herb Crown
Jan 15, 2013 1:28pm

Hi George and Lindsey, the answer is a definiative “YES”. G
Hi George and Lindsey, the answer is a definiative “YES”. George is correct, we covered this a while back and it goes back even further than he referenced, please check this link:

A common LA test system, the STA Clot LA, from Stago, contains polybrene which will handle upto 1 unit/ml heparin.

Herb Crown
St. Louis University Hospital Coagulation Reference Lab

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