Dilute Prothrombin Time (dPT / Tissue Thromboplastin Inhibition)

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Turnaround Time: 2 - 3 days
CPT Code:


Test Type: 1 mL Plasma, frozen


Qualitative detection of lupus anticoagulants (LA) in plasma.6

Improper preparation of the platelet-poor plasma at collection reduces the sensitivity of this assay for LA.6,7 The screening assay can be prolonged in patients with congenital or acquired factor deficiency and will be elevated in individuals on warfarin therapy.7 The reagent contains agents that neutralize unfractionated heparin at plasma levels up to 1.0 unit/mL.7 Samples with levels higher than this can produce anomalous results.7 No single LA test can detect all LA-positive patients. The ISTH recommends that any sample suspected of having LA be tested using two or more LA screening tests.6

Lupus anticoagulants are antibodies which inhibit one or more of the in vitro phospholipid-dependent tests of coagulation (eg, APPT, KCT, dRVVT, dPT). Recently, the SCC Subcommittee for the Standardization of Lupus Anticoagulants provided guidelines for the laboratory diagnosis of LA.6 No single screening test can detect all LA-positive patients. The ISTH recommends that any sample suspected of having LA be tested using two or more LA screening tests.6,9 The other screening tests commonly used to detect LA assess inhibitors of the intrinsic pathway (aPTT-LA) and the common pathways (dRVVT). The dPT assay screens for the phospholipid-dependent inhibitors of a different part of the coagulation cascade, the extrinsic pathway.10

The standard prothrombin time (PT) is usually normal in patients with LA because the thromboplastin reagent used in this assay typically contains a high concentration of phospholipids;11 however, in the dPT assay, the thromboplastin reagent is diluted, increasing assay sensitivity for phospholipid-dependent inhibitors of the extrinsic pathway.11 Several reports have suggested that a dPT assay using recombinant tissue factor and synthetic phospholipids can be sensitive for LA.11,12 The use of a higher phospholipid concentration confirmatory test allows for determination of the phospholipid dependence of the inhibitor.6

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. 1997 Jan; 107(1):105-110. PubMed 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. PubMed 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; 107(6):681-683. PubMed 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. PubMed 10539100

6. Brandt JT, Triplett DA, Alving B, Scharrer I. Criteria for the diagnosis of lupus anticoagulants: An update. On behalf of the Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibody of the Scientific and Standardization Committee of the ISTH. Thromb Haemost. 1995 Oct; 74(4):1185-1190. PubMed 8560433

7. Anticlot dPT®. American Diagnostica. 2005, Document N824CEIE (C)ADI2005rev1003.

8. Arnout J, Vanrusselt M, Huybrechts E, Vermylen J. Optimization of the dilute prothrombin time for the detection of the lupus anticoagulant by use of a recombinant tissue thromboplastin. Br J Haematol. 1994 May; 87(1):94-99. PubMed 7947261

9. Triplett DA. Use of the dilute Russell viper venom time (dRVVT): Its importance and pitfalls. J Autoimmun. 2000; 15(2):173-178. PubMed 10968905

10. Forastiero RR, Cerrato GS, Carreras LO. Evaluation of recently described tests for detection of the lupus anticoagulant. Thromb Haemost. 1994 Nov; 72(5):728-733. PubMed 7900080

11. Greaves M, Cohen H, MacHin SJ, Mackie I. Guidelines on the investigation and management of the antiphospholipid syndrome. Br J Haematol. 2000 Jun; 109(4):704-715. PubMed 10929019

12. Liestol S, Jacobsen EM, Wisloff F. Dilute prothrombin time-based lupus ratio test. Integrated LA testing with recombinant tissue thromboplastin. Thromb Res. 2002; 105(2):177-182. PubMed 11958810

Collection Details:

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.

Collection Instructions:

Blue-top (sodium citrate) tube.

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.