Lupus Anticoagulant

Rivaroxaban Causes False LAC Positive

George reviewed this question posted to the American Society for Clinical Laboratory Science Consumer Web Forum: “After DVT/PE helped by TPA/heparin and now on Xarelto 4 weeks, my first blood draw shows factor VIII 228%, DRVVT screen 126 sec, confirmation 61 sec, normalized ratio 1.96, but hex phase phospholipid normal range and antiphospholipid normal range. […]

Anticoagulant Therapy

Do DOACs Interfere with LAC Testing?

Bonnie Jo Taylor, MHS, MT(ASCP)SH, of Shreveport, LA answers inquiries on the American Society for Clinical Laboratory Science Consumer Web Forum. She and I recently collaborated on this question from Dr. J. S.: “Does Pradaxa anticoagulant Rx affect any of the usual tests for anti-phospholipid antibodies?” Our answer was… Thank you for your question. Yes, Pradaxa […]

Lupus Anticoagulant

DRVVT Divisor

Maria Cordova, Mayo Labs, asks, How would calculate your DRVVT screen divisor? Hello, Maria, and thank you. You’ve opened a provocative topic and inspired me to relive fun we had with our provocative September 25, 2015 post on this subject, “Don’t Normalize the DRVVT.” This attracted perhaps the most attention of any 2015 topic. I’ll […]

Lupus Anticoagulant

Elevated Protein C Activity

From colleague and friend Kelly Townsend, Tricore Laboratories, Albuquerque: We periodically see elevated protein C activity results in our rheumatology patients. We’ve been wondering what might be leading to this finding. They do not all have positive LA, and in fact tend to have PTT‘s in the lower half of the reference interval (sometimes quite […]

Lupus Anticoagulant

Mixing Studies and the Rosner Index

Here is another excellent question from Sheila Minor: We use the Rosner index for both interpretation of a PT or PTT mixing study and for LA testing, in which we follow up the DRVVT confirm and ratio with a 50:50 DRVVT mix to resolve discrepancies. Most references state that a Rosner index value of 15 or […]

Lupus Anticoagulant

Don’t Normalize the DRVVT Ratio

A new note from Sheila Minor: Hi George! Thank you for responding to my question in regard to using an intermediate sensitivity PTT reagent for general screening and heparin management and a LAC-sensitive reagent like PTT–LA for LAC detection. I have one more question about reporting the results of the DRVVT/Confirm and Ratio results. I […]

Lupus Anticoagulant

More on PTT Sensitivty for LAC

Here is a provocative follow-up from Dr. Ning Tang describing PTT reagent sensitivity to LAC: Hi, Prof George, We performed an experiment to compare APTT of samples with or without LAC by different APTT reagents. The results suggest that the type of activator in APTT reagent seems not to be the determinant of sensitivity for […]

Lupus Anticoagulant

Detecting Coagulants in Patients with LAC

From Dr. Ning Tang: Hi, George, We have a patient with strong lupus anticoagulant (LAC or LA). Diluting the plasma can’t recover the intrinsic factor activities (all <20%), also all results of the intrinsic factor inhibitors were positive. Hence we replaced the APTT reagent by a silica clotting time reagent that contains sufficient phospholipid and […]

Lupus Anticoagulant

Mixing Study: LA Effect?

Hello Mr. Fritsma! My name is Agustin Rodriguez and I am a haematologist from Spain. I have a question for you, if you are so kind to ansxwer it: I have a patient with a lupus anticoagulant. His PTT (aPTT) is 46 s; normal aPTT is 30 s in my laboratory. The inmediate mixing study 1:1 with […]

Lupus Anticoagulant

Hex-phase Only for LA?

From Lorna Bogertman, Valley Health: Hello George, I have a question concerning lupus anticoagulant (LA) testing. We have had several requests from physicians to perform hexagonal phase LA testing only. Is it valid to perform this test without the rest of the LA profile? We have found that if we performed Stago’s LA-sensitive partial thromboplastin time […]

Lupus Anticoagulant

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George Fritsma is a medical laboratory scientist, educator, and author. George holds faculty appointments with Rutgers University and Michigan State University, and is a member of the International Society on Thrombosis and Hemostasis, American Association of Clinical Chemists, and American Society for Clinical Laboratory Science.

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