Hexagonal Phase Phospholipid

Single-analyte tests

• Hexagonal Phase Phospholipid (HPP) 117838

  Plasma · Fasting not stated · Turnaround 2 - 3 days

  Method and collection

  Method

  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 the laboratory defined cutoff.

  Preparation

  Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter.

  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.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 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, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used.4,5 When noncitrate 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 recentrifuge 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.

  Reference notes

  0–8 sec Patients with a prolonged aPTT or lupus sensitive aPTT screening test: • Reduction of the aPTT result by more than a laboratory-determined cutoff (test result that is elevated) as the result of adding hexagonal phase phospholipid (HPP) is consistent with the presence of a phospholipid-dependent inhibitor (lupus anticoagulant). • Failure of the HPP to reduce the aPTT result (test result that falls in the normal reference interval) can be interpreted as a possible indication of the presence of one or more specific factor inhibitors.

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