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HEXAGONAL PHASE PHOSPHOLIPID
Message"Avoid warfarin (Coumadin®) therapy for two weeks and heparin therapy for two days prior to the test. Do not draw from an arm with a heparin lock or heparinized catheter.
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Test Code
117020
Alias/See Also
Neutralization, Hexagonal Phase Phospholipid
Staclot LA
Staclot LA
CPT Codes
85598
Preferred Specimen
"Plasma, frozen
2 mL
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2 mL
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Minimum Volume
"1 mL
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Instructions
"If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted.
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Transport Container
"Blue-top (sodium citrate) tube
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Specimen Stability
Freeze
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
"Gross hemolysis; clotted specimen; frozen specimen thawed in transit; tubes <90% full; improper labeling; specimen collected in tube other than 3.2% citrate
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Methodology
"Clotting time using an activated partial thromboplastin time (aPTT) reagent is determined both in the presence and in the absence of HPP. The assay is considered to be positive for lupus anticoagulant when addition of HPP reduces the aPTT by more than 8 seconds. "
Limitations
"Plasma heparin levels >1 IU/mL may interfere with this test.7 Platelets are a rich source of phospholipid that can neutralize LA. Improper preparation of the platelet-poor plasma at collection reduces the sensitivity of this assay for LA. This test is subject to false-positive cross-reactivity with factor VIII inhibitors.8
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Reference Range
"Patients with a prolonged aPTT or aPTT-LA screening test:
• Reduction of the aPTT result by more than eight seconds (test result more than eight seconds) as the result of adding hexagonal phase phospholipid (HPP) is consistent with the presence of a ph
• Reduction of the aPTT result by more than eight seconds (test result more than eight seconds) as the result of adding hexagonal phase phospholipid (HPP) is consistent with the presence of a ph
Clinical Significance
"Lupus anticoagulants are nonspecific inhibitors of phospholipid-dependent in vitro coagulation tests.6 The HPP assay takes advantage of the fact that many LA antibodies specifically recognize the HPP phospholipid configuration as an antigenic epitope. Addition of HPP to the reaction mixture serves to neutralize the inhibitory effect caused by LA antibodies and does not neutralize most factor-specific antibodies.9,10 The assay design includes several features that serve to improve the clinical utility of the test.7 The aPTT reagent used is diluted to reduce its phospholipid concentration and increase sensitivity to LA. The addition of normal plasma to the test system serves to correct for any clotting time prolongation caused by factor deficiencies in the patient plasma. This improves the specificity for LA by making the test relatively insensitive to factor deficiency. The assay reagent also contains a heparin neutralizer, which makes the test system insensitive to heparin levels up to 1 IU/mL. This assay can be used to detect lupus anticoagulants in patients receiving warfarin therapy.
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