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Print CPT 85613; 85732. If reflex testing is performed, concomitant CPT codes/charges will apply.
Synonyms
- Lupus Anticoagulant
- Lupus Anticoagulant Screen
Test Details
Turnaround Time
2 - 3 days
Use
This test is used for qualitative detection of lupus anticoagulants in plasma.
Limitations
Patients with high clinical suspicion of having APS, but without presence of criteria aPL, are suggested to have “seronegative APS” (SNAPS). These patients may be positive for so-called non-criteria aPL or be negative for the criteria aPL through insufficient sensitivity of the assays.11,24
Inherent to the test principle of phospholipid-based coagulation assays, LAC testing is prone to interferences.
Elevated c-reactive protein interferes in vitro with aPTT testing through its affinity for phospholipids, leading to false-positive results of the LAC test.25
Increased factor VIII (FVIII) coagulant activity is associated with shorter aPTT clotting times and can lead to false-negative LAC aPTT screening assays.26 dRVVT screening is not influenced by FVIII levels as factor X is directly activated by Russell’s viper venom. Increased levels of FVIII can be observed during pregnancy, surgery, inflammation, malignancy and other conditions.27
LAC is often found to be positive during inflammatory conditions, without clear association with a clinical APS phenotype, recently highlighted in patients with coronavirus disease 2019.28 LA positivity after viral and bacterial infections is often transient and not accompanied by the clinical APS phenotype.29
Certain drugs (e.g., antibiotics, antiarrhythmics and chlorpromazine) and to a lesser extent vaccines (e.g., against hepatitis B virus) are also found to be associated with LA activity.29
In the acute setting of thrombosis, increased FVIII levels can lead to false-negative LA assessment, while increased CRP can lead to false-positive LA testing. Therefore, it is not recommended to assess LAC status during the thrombotic event or in patients with acute inflammation. Retesting patients with LAC positivity, at least 12 weeks after the initial finding, is an important strategy in avoiding misclassification of patients with transient LAC.4
Anticoagulation treatment complicates LAC testing and interpretation by prolonging aPTT and dRVVT. LAC testing during anticoagulation treatment is discouraged,4 although it is not always desirable to postpone LAC analysis until treatment cessation.20
Vitamin K antagonists (i.e., warfarin) can cause prolongation of aPTT and dRVVT through production of incomplete coagulation factors by inhibition of vitamin K-dependent gamma carboxylation of factors II (prothrombin), VII, IX and X.30 This acquired factor deficiency can lead to false-positive interpretation of LA testing, especially in the screening step, and false negative in the mixing step.
Unfractionated heparin (UFH), LMWH and heparinoids mainly interfere by indirectly inhibiting thrombin and activated factor X (FXa) action.31 dRVVT and the PTT-LA reagents contain heparin-neutralizing agents, quenching the effect of heparin in vitro.
Direct Oral Anticoagulants (DOACs) directly inhibit thrombin (e.g., dabigatran) or Factor Xa (e.g., apixaban, betrixaban, edoxaban and rivaroxaban),32 with various effects on coagulation tests, even at trough levels, leading to both false-negative and false-positive LA interpretation.33-36 Adsorption of DOACs from plasma prior to testing can overcome DOAC interference in vitro.
Methodology
PTT-LA (lupus-sensitive aPTT) and dRVVT screen; mixing study if screening tests are prolonged; confirmation if the mixing studies do not correct
Related Documents
For more information, please view the literature below.
Additional Information
Antiphospholipid syndrome (APS) represents a serious clinical condition in which patients may be at high risk for thrombosis, pregnancy/fetal morbidity/mortality, or other multi-system clinical presentations.1 The latest APS classification criteria2 identify patients as having definite APS based on a clinical and laboratory scoring system as the entry criterion and persistent presence of certain antiphospholipid antibodies (aPL). These aPL tests are also more broadly used to diagnose or exclude APS.3
Antiphospholipid syndrome (APS) is an acquired autoimmune disorder that manifests clinically as recurrent venous, arterial and/or small vessel thrombosis and/or fetal loss in the context of persistently positive antiphospholipid antibodies (aPL).4-9 At least one clinical criterion and one laboratory criterion must be present for a patient to be classified as having APS. The clinical criteria consist of vascular thrombosis and pregnancy morbidity.
Vascular thrombosis is defined as the following:
One or more clinical episodes of arterial, venous, or small-vessel thrombosis in any tissue or organ confirmed by findings from imaging studies, Doppler studies or histopathology.
Thrombosis may involve the cerebral vascular system, coronary arteries, pulmonary system (emboli or thromboses), arterial or venous system in the extremities, hepatic veins, renal veins, ocular arteries or veins or adrenal glands.
Investigation is warranted if a history of deep venous thrombosis, pulmonary embolism, acute ischemia, myocardial infarction (MI) or stroke (especially when recurrent) is present in a younger individual (males <55 y; females <65 y) or in the absence of other risk factors.
Pregnancy morbidity is defined as the following:
One or more late-term (>10 weeks' gestation) spontaneous abortions.
One or more premature births of a morphologically healthy neonate at or before 34 weeks’ gestation because of severe preeclampsia or eclampsia or severe placental insufficiency.
Three or more unexplained, consecutive, spontaneous abortions before 10 weeks’ gestation.
Besides the criteria currently regarded as classification criteria for APS, other manifestations such as thrombocytopenia, autoimmune hemolytic anemia, livedo reticularis, neurologic manifestations, nephropathy and valvular heart disease are associated with presence of aPL.10-13
In addition to the clinical criteria, at least one of the following laboratory criteria is necessary for the classification of APS:4-8
Presence of lupus anticoagulant (LA) in plasma on two or more occasions at least 12 weeks apart.
Presence of moderate to high levels of anticardiolipin (aCL; IgG or IgM) in serum on two or more occasions at least 12 weeks apart.5
Presence of moderate to high levels of anti–beta-2 glycoprotein I antibodies (β2GP1; IgG or IgM) in serum on two or more occasions at least 12 weeks apart.5
Lupus Anticoagulant Testing
Current LA testing guidelines recommend use of at least two tests based on different assay principles before excluding LA, recommending the activated partial thromboplastin time (aPTT) and dilute Russell viper venom time (dRVVT).4,6,14 The aPTT is based on contact activation, and the dRVVT is based on factor (F)X activation.15,16
Lupus anticoagulants (LA) are nonspecific autoantibodies that extend the clotting time of phospholipid-dependent clotting assays.4-8 LA do not specifically inhibit individual coagulation factors; rather they neutralize anionic phospholipid-protein complexes that are involved in the coagulation process. The International Society of Thrombosis and Haemostasis (ISTH) has established criteria for the identification of LA by clot-based assays.4 Prolongation of clot-based assays is dependent on the sensitivity of the reagent employed to detect the presence of LA. Assays are made more sensitive for LA by decreasing the amount of phospholipid in the reagent. The ISTH guidelines call for the use of two LA-sensitive reagent systems in testing for LA as no single test has sufficient sensitivity and specificity.4-8 Both assays are complementary as aPL do not always react in both test systems.17 The most recent update of the ISTH guidelines on LA detection recommends parallel testing of the dilute Russell’s viper venom time (dRVVT) and aPTT.4
The dilute Russell Viper Venom Time (dRVVT) dilute and activated Partial Thromboplastin Time (aPTT-LA) are the most used tests for LA and are specifically mentioned in the guidelines.4 The dRVVT assay is based on direct activation of factor X by an enzyme present in the venom of Russell’s vipers. aPL in patient plasma will react with phospholipid components of the reagent through cofactors and prolong the dRVVT by decreased activity of the prothrombin activator complex.18 The aPTT-LA assay is based on activation of the contact (intrinsic) pathway. Analogous to the dRVVT assay, aPL inhibit phospholipid-dependent steps in the aPTT coagulation pathway. A prolonged clotting time in either screening test is followed by demonstration of phospholipid dependence and inhibitory properties in confirmatory and mixing tests, respectively, which are modifications of the parent screening test. In order for an extended screening result to be interpreted as a lupus anticoagulant, the assay clotting time must exhibit correction (reduced clotting time) on re-addition of phospholipid in what is referred to as a “confirmation” assay.
The Labcorp LA reflex testing procedure was designed based on the recommendations of the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the ISTH updated in 2020.4 The three-step procedure starts with performance of the two LA-sensitive screening tests (PTT-LA and dRVVT). Samples with prolonged screening results for either of these tests are further tested by a mixing test (to exclude a deficiency in coagulation factor as the cause of the extended screening test) and a confirmation test (to ascertain if a phospholipid dependent inhibitor (LA) is detected). The LAC testing is considered positive if one of the two test systems gives a positive confirmation result.4
Specimen Requirements
Information on collection, storage, and volume
Specimen
Plasma, frozen
Volume
2 mL
Minimum Volume
1 mL (Note: This volume does not allow for repeat testing.)
Container
Blue-top (sodium citrate) tube
Storage Instructions
Freeze.
Causes for Rejection
Severe hemolysis; improper labeling; clotted specimen; specimen diluted with IV fluids; samples thawed in transit; improper sample type; sample out of stability
Collection
Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.19 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.20,21 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube.22,23 When non-citrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and re-centrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a Labcorp PP transpak frozen purple tube with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.