Overview
Lupus anticoagulant testing detects antibodies that prolong phospholipid-dependent clotting times in vitro yet are associated with thrombosis in vivo.
Clinical Importance
Evaluate antiphospholipid syndrome laboratory criteria
Investigate unexplained aPTT prolongation and selected thrombosis/pregnancy morbidity pathways
Specimen Requirements
- Specimen: platelet-poor plasma prepared from whole blood
- Tube: light-blue top; 3.2% sodium citrate (0.109 mol/L)
- Anticoagulant ratio: 9:1 blood-to-citrate (CLSI H21); fill to the tube fill line
- Handling: invert gently; transport promptly; avoid traumatic draws and line heparin contamination
- Processing: centrifuge to platelet-poor plasma per institutional protocol before testing
- Stability: assay-specific (CLSI H21). aPTT is generally less stable than PT; do not exceed validated time/temperature limits for the ordered tests.
Analytical Method
A three-step approach is used: (1) screening with LA-sensitive assays (commonly dRVVT and/or LA-sensitive aPTT), (2) mixing studies to demonstrate inhibitor pattern, (3) phospholipid dependence confirmation (excess phospholipid shortens the clotting time). ISTH/SSC guidance informs panel design. Persistently positive results ≥12 weeks apart are required for APS classification criteria.
Instruments Used
Automated analyzers
- Automated coagulometers running dRVVT and LA-sensitive aPTT reagent pairs
Manual methods
- Manual tilt-tube clotting methods in specialized reference settings
Reference Values
Typical adult SI examples below follow widely published international hematology practice (e.g., Dacie and Lewis; Henry's). Always interpret against the method- and demographics-specific interval printed on the patient report (CLSI EP28-A3c). Neonatal, pediatric, pregnancy, and altitude intervals differ.
Negative LA expected in the absence of phospholipid-dependent inhibitors. Positive/negative calls follow normalized ratios and reagent cutoffs; method-specific (CLSI EP28 does not replace APS persistence criteria).
Interpretation
Common Causes of Increased Results
- LA positive; interpret with aCL/anti-β2GPI, clinical criteria, and repeat testing for persistence
Common Causes of Decreased Results
- LA negative; does not exclude APS if solid-phase antibodies are positive
Clinical Significance
- APS laboratory panels
- Unexplained aPTT prolongation workups
Factors Affecting Results
Pre-analytical
- Heparin contamination prolonging clotting times
- Underfilled citrate tubes
- Testing during acute thrombosis or while on some anticoagulants without method-aware interpretation
Analytical
- Reagent phospholipid content differences
- Incomplete three-step algorithms
Post-analytical
- Diagnosing APS on a single LA result without solid-phase antibodies and persistence
Advantages and Limitations
Advantages
- Essential APS criterion not replaced by ELISA alone
Limitations
- Affected by anticoagulation
- Requires paired solid-phase aPL testing for complete APS serology
Clinical Pearls
Lupus anticoagulant is a pattern of clotting tests; not a single tube labeled 'LA positive forever.'
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Rodak BF, Carr JH. Rodak's Hematology: Clinical Principles and Applications. 6th ed. Elsevier; 2020.
- Hoffbrand AV, Moss PAH, Pettit JE. Essential Haematology. 8th ed. Wiley-Blackwell; 2019.
- McKenzie SB, Williams JL. Clinical Laboratory Hematology. 4th ed. Pearson; 2022.
- Bain BJ, Bates I, Laffan MA. Dacie and Lewis Practical Haematology. 12th ed. Elsevier; 2017.
- Kaushansky K, et al. Williams Hematology. 10th ed. McGraw-Hill; 2021.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays; Approved Guideline. CLSI document H21-A5. CLSI; 2017.
- Clinical and Laboratory Standards Institute. One-Stage Prothrombin Time (PT) Test and Partial Thromboplastin Time (PTT) Test; Approved Guideline. CLSI document H47-A2. CLSI; 2008.
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Management of Critical- and Significant-Risk Results. CLSI guideline GP47-Ed1. CLSI; 2015.
Frequently Asked Questions
Common questions about using this Lupus Anticoagulant laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Lupus Anticoagulant laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Lupus Anticoagulant. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Lupus Anticoagulant specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Lupus Anticoagulant. Confirm collection details against your laboratory protocol.
Where are Lupus Anticoagulant reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret Lupus Anticoagulant results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for Lupus Anticoagulant?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from Lupus Anticoagulant?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Lupus Anticoagulant?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Hematology topic.
What are the clinical pearls for Lupus Anticoagulant?
See the Clinical Pearls section for concise laboratory practice notes associated with Lupus Anticoagulant. Apply pearls alongside institutional protocols.
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