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Lupus Anticoagulant (LA) Evaluation with Reflex

Test code(s) 7079X

Question 1. How does Quest Diagnostics perform a Lupus Anticoagulant Profile?

Question 2. The PTT-LA is prolonged, yet the interpretive comment states “No Lupus Anticoagulant Detected.” Is this significant?

The PTT-LA is a sensitive, but nonspecific screening test for LA. It may be prolonged if the patient is on anticoagulant therapy (ie, heparin, warfarin, or thrombin inhibitors).

If the patient is not anticoagulated and the result is ≤50 sec then you may want to consider an aPTT with a routine reagent. PTT-LA is a modified aPTT with dilute phospholipids that make it very sensitive to LA. The trade-off for the increased sensitivity is a small percentage of false-positive screens. A compelling clinical history, bleeding, or thrombosis, warrants further investigation.

Question 3. Can I test my patient while he/she is anticoagulated with heparin or warfarin?

For warfarin, the screening tests (PTT-LA, dRVVT) may be prolonged, but the confirmatory tests are good at distinguishing LA from warfarin effect.

For unfractionated heparin, the Hexagonal Phase and both dRVVT tests have heparin neutralizers. It is possible to overwhelm the neutralizing capacity resulting in false- positive confirmatory studies. Expect the PTT-LA to be markedly prolonged.

However, many thought leaders—including the Scientific Subcommittee (SSC) of International Society of Thrombosis and Haemostasis (ISTH) on LA—recommend not testing patients for LA while anticoagulated (Pengo, et al. J Thromb Haemost. 2009;7(10):1737-1740).

Question 4. What is the significance of a “weak” positive Hexagonal Phase Confirm?

The designation of "weak" LA is based on the observation that the Hexagonal Phase Confirm result is just above the cut-off for positivity. This is a laboratory finding only and does not reflect the in vivo thrombophilia potential.

Question 5. The interpretation states that “a Lupus Anticoagulant is detected because 1 of 2 confirmatory tests is positive.” How can this be?

LAs are heterogenous antibodies that differ in titer, avidity, and isotype. This is why the ISTH recommends using two different reagents that evaluate different coagulation pathways (PTT-LA–intrinsic pathway, dRVVT–common pathway) to increase the sensitivity of detection.

This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
Document: FAQS.01 Revision: 2