Lupus Anticoagulant

PTT and C-reactive Protein

From Dean Willett, Precision BioLogic Inc. As I read the 11-8-17 comments from Dr. Elman a bit of a lightbulb went off in my head. I’m sure you’ve seen the various publications that demonstrate the effect of C reactive protein (CRP) on APTT assays. Here are: https://www.ncbi.nlm.nih.gov/pubmed/22224499; and https://biblio.ugent.be/publication/5838447/file/6839536. There have been some proficiency samples […]

Lupus Anticoagulant

LAC Profile: PTT Versus PTT-LA

From “Ari.” Hi George, I stumbled upon your amazing site when researching this question and was wondering if you could shed some light on this. I have a patient who had a DVT. His PCP noted a slightly prolonged aPTT and sent mixing studies. From what I can tell, the aPTT mostly corrected with mix, […]

Lupus Anticoagulant

Is APS Hereditary?

An intriguing case from Heather DeVries, Indiana University Health. Hi George, I have an interesting (cold) case study for you. We recently tested a 44 yo female for lupus antibodies and she had textbook results–nothing equivocal about them. Her history includes a late-term pregnancy loss 12 years ago, and a recent diagnosis of lupus, so […]

Lupus Anticoagulant

ACA Pt Specimens Vs. Calibrators

From Wendy Sutula, Hi, George. We are validating a new vendor’s ACA kit. When we perfom patient ACA tests, the serum samples are frozen at –20 for 2–7 days before tesing. When establishing or validating the reference range for the new vendor’s kit, is it acceptable to use serums which have been collected and frozen […]

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

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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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