Hexagonal Phase Phospholipid (HPP)

CPT: 85598
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Test Details


  • Neutralization, Hexagonal Phase Phospholipid
  • Staclot LA


This test system is designed for the qualitative detection of lupus anticoagulants in plasma.6


Anticoagulant therapy may cause false-positive results. 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


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.

Reference Interval

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.

Additional Information

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.

Specimen Requirements


Plasma, frozen


2 mL

Minimum Volume

1 mL


Blue-top (sodium citrate) tube

Patient 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.


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 N° 49482). Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.

Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.

Storage Instructions


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

Clinical Information

Special Instructions

If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer to Coagulation Collection Procedures for directions.


1. Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997Jan; 107(1):105-110. 8980376
2. Reneke J, Etzell J, Leslie S, Ng VL, Gottfried EL. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998 Jun; 109(6):754-757. 9620035
3. National Committee for Clinical Laboratory Standardization. Collection, Transport, and Processing of Blood Specimens for Coagulation Testing and General Performance of Coagulation Assays; Approved Guideline. 5th ed. Villanova, Pa: NCCLS; 2008. Document H21-A5:28(5).
4. Gottfried EL, Adachi MM. Prothrombin time and activated partial thromboplastin time can be performed on the first tube. Am J Clin Pathol. 1997 Jun; 107(6):681-683. 9169665
5. McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999 May-Jun; 12(3):137-139. 10539100
6. Brandt JT, Triplett DA, Alving B, et al. Criteria for the diagnosis of lupus anticoagulants: An update. On behalf of the Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibody of the Scientific and Standardisation Committee of the ISTH. Thromb Haemost. 1995; 74(4):1185-1190. 8560433
7. StaClot LA [package insert]. Parsippany, NJ: Diagnostica Stago; April 2001. Document #23142 01.
8. Brandt JT, Barna LK, Triplett DA. Laboratory identification of lupus anticoagulants: Results of the Second International Workshop for Identification of Lupus Anticoagulants. On behalf of the Subcommittee on Lupus Anticoagulants /Antiphospholipid Antibodies of the ISTH. Thromb Haemost. 1995 Dec; 74(6):1597-1603. 8772243
9. Rauch J, Tannenbaum M, Janoff AS. Distinguishing plasma lupus anticoagulants from antifactor antibodies using hexagonal (II) phase phospholipids. Thromb Haemost. 1989; 62(3):892-896. 2512678
10. Triplett DA, Barna LK, Unger GA. A hexagonal (II) phase phospholipid neutralization assay for lupus anticoagulant identification. Thromb Haemost. 1993; 70(5):787-793. 8128436


Adcock DM, Gosselin R. Direct oral anticoagulants (DOACs) in the laboratory: 2015 review. Thromb Res. 2015 Jul; 136(1):7-12. 25981138


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
117838 Hexagonal Phase Phospholipid 3282-1 117839 Hexagonal Phase Phospholipid sec 3282-1
Reflex Table for Hexagonal Phase Phospholipid
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 117800 Comment 117800 Comment N/A
Reflex Table for Hexagonal Phase Phospholipid
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 117841 Comment 117841 Comment 77202-0

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