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Variable Findings in One-Stage Clotting Assays in a Patient with Waldenstrom’s Macroglobulinaemia

S. Platton1, A. McCormick2, A. Riddell3, E. Bromidge2, C. Fenoo4, G.W. Moore2,5, C. Boshier4

1Haemophilia Centre, Royal London Hospital, Barts Health NHS Trust, London, United Kingdom, 2Haemostasis and Thrombosis Centre, Viapath Analytics, St Thomas' Hospital, London, United Kingdom, 3Katharine Dormandy Haemophilia and Thrombosis Centre, Royal Free NHS Foundation Trust, London, United Kingdom, 4Haematology Laboratory, Queen's Hospital, Barking,Havering and Redbridge University Hospitals NHS Trust, London, United Kingdom, 5Specialist Haemostasis Unit, Addenbrooke's Hospital, Cambridge University Hospital NHS Foundation Trust, Cambridge, United Kingdom

Abstract Number: PB0604

Meeting: ISTH 2020 Congress

Theme: Diagnostics and OMICs » Laboratory Diagnostics

Background: A patient with Waldenstrom’s Macroglobulinaemia had samples sent to Laboratory-1 who found a raised prothrombin time (PT) ratio (3.7), activated partial thromboplastin time (APTT) ratio (1.3), factor (F)V≤1IU/dL, and FVII 18IU/dL. Samples were referred to Laboratory-2 for confirmation and to Laboratory-3 and Laboratory-4 in an inter-laboratory exchange.

Aims: Establish consensus between laboratories in diagnosis of rare inhibitors.

Methods: Laboratories performed screening, one-stage clotting assays (OSCA) and inhibitor screening by their routine methods.

Results:
Laboratory-2 measured FVII≥59IU/dL, FII≥41IU/dL and FX≥23IU/dL (non-parallel curves), and FV≤1.0IU/dL at all dilutions. A Bethesda-principle inhibitor assay was consistent with a FV-inhibitor (18.1BU/mL). Lupus anticoagulant (LA) was detected by dilute Russell’s viper venom time (DRVVT), dilute APTT and Taipan Snake Venom Time (TSVT) confirmed by Ecarin Clotting Time (ECT).
Laboratory-3 measured FV and FVII activity below 1IU/dL, a FV-inhibitor (16.6BU/mL), a FVII-inhibitor (not quantified) and LA detected by DRVVT, dilute APTT and TSVT/ECT.
Laboratory-4 found normal levels of FII, FV, FVII and FX using PT reagent, but reduced FX using an APTT-based OSCA, and a FX-inhibitor (16BU/mL). No LA was detected by DRVVT or Silica Clotting Time.
Further OSCA were performed using a variety of different reagents on new samples (see table 1).

  Lab 1 Lab 2 Lab 3 Lab 4
  Aug 19 Sept 19 Nov 19 Sept 19 Nov 19 Sept 19 Nov 19
Factor II [IU/dL]   40.5Innovin 69.0Innovin 92.3ThromborelS 92.6ActinFS >10.2Innovin >36.9Innovin 52Recombiplastin 49Recombiplastin
Factor V [IU/dL] <1Innovin <1.0Innovin <1.0Innovin 95.8ThromborelS 162.8ActinFS <1.0Innovin 70.7Antigen >28.8Innovin 107.7Antigen 60Recombiplastin 79Recombiplastin
Factor VII [IU/dL] 18Innovin >=59.2Innovin >=73.1Innovin 77.4ThromborelS <1.0Innovin >6.2Innovin 49Recombiplastin 46Recombiplastin
Factor X [IU/dL]   >=22.7Innovin >=39.4Innovin 77.5ThromborelS 81.1ActinFS >11.7Innovin 58.6Antigen >19.6Innovin 58Recombiplastin 17Synthasil 58Recombiplastin 14Synthasil
Factor VIII [IU/dL]   108.5Chromogenic 116.5ActinFS 60.8ActinFSL 82.9PathromtinSL 89.6Chromogenic       106Synthasil
Factor IX [IU/dL]   59.1Actin FS 77.2ActinFS 47.4ActinFSL 61.8PathromtinSL       20Synthasil
Factor XI [IU/dL]     61.5ActinFS 37.8ActinFSL 52.3PathromtinSL       25Synthasil
Factor XII [U/dL]     55.8ActinFS 49.0ActinFSL 55.8PathromtinSL       55Synthasil

[Factor Assay Results]

Using LA-sensitive reagents, PT and APTT were prolonged even when mixed with normal plasma, and OSCA showed non-parallel curves, indicating the presence of an inhibitor. Using LA-insensitive PT and APTT reagents showed mildly prolonged clotting times and normal factor assays.

Conclusions: This patient had a strong LA that interfered with all OSCA performed with LA-sensitive reagents, even at high dilutions. These findings highlight: that LA can affect PT and/or APTT; the importance of using LA-insensitive reagents for performing OSCA; the importance of checking parallelism in OSCA, even when factor levels appear to be normal; and that even expert laboratories find such scenarios challenging.

To cite this abstract in AMA style:

Platton S, McCormick A, Riddell A, Bromidge E, Fenoo C, Moore GW, Boshier C. Variable Findings in One-Stage Clotting Assays in a Patient with Waldenstrom’s Macroglobulinaemia [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/variable-findings-in-one-stage-clotting-assays-in-a-patient-with-waldenstroms-macroglobulinaemia/. Accessed November 29, 2023.

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