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29 January 2025: Articles  Malaysia

Impact of Lupus Anticoagulant on INR Using Recombinant Prothrombin Time Reagent

Unusual clinical course, Challenging differential diagnosis, Unusual or unexpected effect of treatment, Diagnostic / therapeutic accidents, Clinical situation which can not be reproduced for ethical reasons

Fatmawati Kamal ORCID logo1ABCDEF*, Halimatun Radziah Othman2ABCDEF

DOI: 10.12659/AJCR.945579

Am J Case Rep 2025; 26:e945579

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Abstract

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BACKGROUND: Lupus anticoagulants (LA) can interfere with routine coagulation tests such as the activated partial thromboplastin time (aPTT) and prothrombin time (PT). The international normalized ratio (INR) is derived from PT and is used to monitor warfarin therapy. A positive LA result is one of the laboratory criteria of the 2023 ACR/EULAR antiphospholipid syndrome (APS) classification criteria. We report a case in which LA interfered with INR measurement in an APS patient.

CASE REPORT: Our patient was a 45-year-old man who had experienced multiple episodes of thromboembolism. His INR was consistently high, despite not being on any anticoagulant. Our laboratory used a recombinant PT reagent, Siemens Healthineers Dade® Innovin® on a fully automated coagulometer, the Sysmex CS-2500. PT measurements were repeated using 2 different analyzers, the Sysmex CA-104 and Werfen ACL Top 550 CTS. The PT results were 40.5 s (reference range (RR): 9.3-10.8 s) and 56 s, using Sysmex CS2500 and CS104, respectively. However, the PT was 13.4 s (RI: 10.3-12.7 s) using Werfen ACL Top 550 CTS. We retested the sample using Thromborel® S, a tissue-derived PT reagent, and PT was found to be within the reference range. The patient tested positive for LA, anti-cardiolipin, and anti-beta2 glycoprotein I antibodies.

CONCLUSIONS: LA can falsely prolong the PT when a recombinant PT reagent is used. When we retested the plasma using a tissue-derived PT reagent – Thromborel® S – PT was within normal limits. Thus, it is important to acknowledge that LA can react differently with different PT reagents.

Keywords: Antiphospholipid Syndrome, Lupus Coagulation Inhibitor, Prothrombin Time

Introduction

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by vascular thromboembolic events and persistent antiphospholipid antibodies. A diagnosis of APS should be suspected in young adults with at least 1 unexplained thromboembolic event or severe obstetric complication such as severe pre-eclampsia or placental insufficiency. Evidence of persistent antiphospholipid antibodies such as lupus anticoagulants (LA), anti-cardiolipin (aCL), and anti-beta2 glycoprotein I (aβ2GPI) antibodies must be present to support the diagnosis. APS can occur with or without other autoimmune diseases like systemic lupus erythematosus (SLE) [1]. LA are non-specific coagulation inhibitors that can cause in vitro prolongation of routine coagulation tests such as the activated partial thromboplastin time (aPTT) and prothrombin time (PT), which are phospholipid-dependent clotting times. The detection of LA requires 2 tests based on different principles. The first test should be the diluted Russell’s viper venom time (dRVVT) and the second test should be a sensitive aPTT [2]. The LA-sensitive aPTT re-agent contains a small amount of phospholipid and uses silica as an activator. LA should be considered positive if 1 of the 2 test systems gives a positive result in the 3 steps (screen-mix-confirm) [2]. The aCL and aβ2GPI antibodies can be detected in solid-phase assays, such as enzyme-linked immunosorbent assay (ELISA) [3]. We present a case of an unexpected prolonged PT in a patient with antiphospholipid syndrome.

Case Report

A 45-year-old man with stage 3 chronic kidney disease, mitral valve replacement, and multiple episodes of thromboembolic events presented to our facility for neurological rehabilitation. He was on rivaroxaban 15 mg once daily. His initial blood test in December 2021 showed a hemoglobin level of 11.6 g/dL and a platelet count of 81×109/L (Table 1). Based on his clinical history, he was suspected of having APS and was referred to a clinical hematologist for further management.

He was seen by the clinical hematologist on 5 January 2022. His blood sample was sent for a full blood count and coagulation study. His blood investigations showed normochromic normocytic anemia with thrombocytopenia and abnormal coagulation study (Table 1).

His INR was 8.5 and although he did not have any history of bleeding, he was admitted for further investigation. His blood sample was then sent for thrombophilia study and outsourced to a reference laboratory. Meanwhile, he was kept on rivaroxaban 15 mg once daily and started on subcutaneous enoxaparin 60 mg/0.6 mg twice daily. His platelet counts remained consistently low during admission, ranging between 61×109/L and 81×109/L. His coagulation study was consistently abnormal, with mean PT, INR, and aPTT of 57.7 s, 6.0, and 36.6 s, respectively (reference range (RR) PT: 9.3–10.8 s, INR: <1.2, aPTT: 22.2–33 s). The patient was discharged home a week later with only subcutaneous enoxaparin. His INR on discharge was 4.0.

The coagulation study was repeated during clinic follow-up on 20 January 2022 and 24 January 2022, showing that his PT, INR, and aPTT results were still abnormal. A PT mixing test was performed on 24 January 2021. aPTT mixing was not done because the patient was on low-molecular-weight heparin (LMWH). At this point, he had been off rivaroxaban for about 10 days and was only on subcutaneous enoxaparin. PT showed non-correction (Table 1). Thus, the possibility of a plasma inhibitor needed to be excluded. The result for the lupus anticoagulants was still pending, as it had been outsourced earlier. Additionally, the clinician ordered factor VII antigen and inhibitor levels, which were also outsourced to a reference laboratory. The results for PT and INR from the outsourced laboratory were slightly prolonged at 13.8 s and 1.8. His factor VII level was 78.4% and no FVII inhibitor was detected (Table 2).

An investigation into the cause of the discrepancy of results between the 2 laboratories was carried out on 9 February 2022 assisted by the application specialist from Sysmex. Sysmex CS-2500 was used at our laboratory to run all routine coagulation testing, which operates using a photo-optical method. The application specialist also brought the portable Sysmex CA-104 to run PT at our laboratory, and the reference laboratory. PT was also performed using the Werfen ACL Top 550 CTS at the reference laboratory. The findings are shown in Table 3. Two weeks later, the application specialist ran another test on different PT reagents on Sysmex CS-2500. The findings are shown in Table 4.

The PT was 13.1s with Thromborel® S, compared to 41.3 s and 37.9 s with the different lots of Siemens Dade® Innovin®. Based on these findings, the PT reagent was changed to Thromborel® S and the patient was started on warfarin 3 mg once daily on 2 March 2022. While waiting for the laboratory to establish the new mean normal PT (MNPT) for Thromborel® S, the coagulation screen was sent to our satellite laboratory, which uses Stago STA Compact Max (Stago Diagnostica). This analyzer uses a mechanical viscosity-based detection system in which a magnetic sensor is used to detect the movement of a steel ball within the test solution. PT is the time taken to detect the change or reduction in the ball movement, indicating clot formation, while the photo-optical method detects a change in the optical density (OD) of a test sample. PT in this case was calculated as the time taken for clot formation, indicated by a drop in photo-density.

The initial PT and INR were 16.2 s and 1.2, respectively. It was slightly more prolonged than the upper-limit normal of 14 s. LA does not seriously interfere with PT measurement with this system because it does not use Siemens Dade® Innovin®. Neoptimal was not as sensitive to LA as the Siemens Dade® Innovin®. The MNPT was established a month later and we were able to run the patient’s sample in-house using the new PT reagent in April 2022. The serial PT/INR results are shown in Table 5.

The results of the thrombophilia study were received on 29 March 2022. LA was reported as positive, whereas IgG aCL and aβ2GPI were 118.709 GPL/mL and 214.325 U/mL, respectively. The tests for protein C, protein S, antithrombin, activated protein C resistance (APCR), and factor V Leiden mutation were not done. The reference laboratory used diluted Russell’s viper venom time (dRVVT) and silica clotting time (SCT) to detect LA. IgG aCL and IgG aβ2GPI were measured using standardized solid-phase assays. The patient continued to come for his clinic appointments regularly until was lost to follow-up 1 year later.

Discussion

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by thromboembolic events and/or pregnancy complications, in the presence of persistent antiphospholipid (aPL) autoantibodies, which are lupus anticoagulants (LA), aCL and aβ2GPI [1]. The preliminary classification criteria for antiphospholipid syndrome were introduced at Sapporo in 1999 to provide uniformity and consensus in classifying APS in clinical studies [4]. The classification was later updated in 2006 as the revised Sapporo Classification Criteria, which have been used in clinical practice. However, because of the heterogeneity of the disease, diagnosis in clinical settings remains a challenge [5]. Certain clinical manifestations associated with APS were not included in the revised Sapporo Classification Criteria. The American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR) through a collaborative effort released the latest APS classification criteria in 2023, featuring 6 clinical and 2 laboratory domains, which improve the identification of patients for APS research [3].

Lupus anticoagulants (LA) are non-specific plasma inhibitors. They are associated with thrombosis, but bleeding can also occur when associated with hypoprothrombinaemia [6]. In clinical practice, a mixing test is usually performed whenever there is an abnormal prolonged PT or aPTT by mixing an equal volume of the patient’s plasma and normal pooled plasma. PT and/or aPTT will be repeated using the mixture. The Rosner Index (RI) is used to determine whether full or partial correction of the clotting has been achieved. A low index value of 10 or lower indicates correction or factor deficiency, whereas 15 and above indicates no correction or presence of inhibitor. A value between 10 and 15 is inconclusive and the test should be repeated. The mixing test for this patient showed non-correction (RI=39). Thus, an inhibitor may have been present. The most likely inhibitor in this patient was LA, given the clinical history and presentation. His factor VII antigen was within normal range and no inhibitor was detected. FVII deficiency is a rare coagulation factor deficiency. The development of FVII inhibitors is associated with severe FVII deficiency (FVII antigen <10%) in those who received recombinant FVII as factor replacement treatment [7].

Our patient was on rivaroxaban when his initial blood samples were sent. His coagulation results were abnormal. Subsequent results showed significant prolongation of PT compared to aPTT. Previous studies have shown that rivaroxaban can cause PT prolongation but does not affect aPTT [8]. Douxfils et al reported a dose-dependent prolongation of PT due to rivaroxaban, and Siemens Dade® Innovin® was shown to be the least affected [9].

LA rarely interferes with PT/INR measurement, unlike aPTT. This is because PT reagents contain higher concentrations of phospholipids than aPTT reagents and neutralize the effect of LA. However, PT/INR may still be affected by LA in some patients because of the different phospholipid amounts and composition [10]. Our patient’s PT/INR results were prolonged when Siemens Dade® Innovin® was used. However, the PT/INR results were only slightly prolonged when Werfen HemosIL RecombiPlasTin® 2G assay was used, even though both PT reagents contain recombinant thromboplastins. The PT/INR produced with RecombiPlasTin® 2G assay was similar to the PT/INR results produced with Siemens Thromborel® S and Stago STA®-NeoPTimal, which contain tissue-derived thromboplastins. Studies have shown that recombinant human thromboplastins are more sensitive to the presence of LA, which could be due to the different phospholipid composition and concentration [11,12]. Tissue-derived thromboplastins may be contaminated with traces of FVII and activated FVII (FVIIa), making them less sensitive to FVII deficiency compared to recombinant thromboplastins [11]. A case report stated that Siemens Dade® Innovin® was more sensitive to LA compared to Siemens Thromborel® S [13]. Another possible reason for the different PT/INR results could be the interaction of LA with the recombinant replicated tissue factor [14].

The results for LA, aCL, and aβ2GPI were positive for all 3 antibodies. Testing for LA was done while the patient was on enoxaparin, and anti-Xa activity levels were not available at the point of blood sampling. The International Society on Thrombosis and Haemostasis recommended that for patients on low-molecular-weight heparin (LMWH), samples should be taken, when feasible, at least 12 hours after the last dose of LMWH and as near as possible to the next dose, with anti-Xa activity levels checked alongside the LA test [12]. LMWH rarely affects LA testing using diluted Russell’s viper venom time (dRVVT) because the reagent contains heparin neutralizers and can douse the therapeutic levels of heparin (up to 1U/mL) [2].

Thrombocytopenia is included in Domain 6 of the 2023 ACR/EULAR antiphospholipid syndrome classification criteria, in which the presence of a true thrombocytopenia with an otherwise unexplained platelet count of between 20 and 130×109/L, on repeat testing, is a criterion for APS [3]. Our patient’s platelet count ranged from 59 to 127×109/L until his last clinic follow-up in April 2023. Initially, rivaroxaban was stopped because it was thought to have been the cause of thrombocytopenia in this patient. However, even after cessation of the anti-Xa, the platelet count did not return to normal. Thus, thrombocytopenia can be immune-mediated in the setting of APS, as reported by some studies [16]. Rivaroxaban has been reported to cause thrombocytopenia in non-APS patients [17]. Our patient was also mildly anemic, with hemoglobin levels ranging between 9.7 g/dL and 12.1 g/dL (mean 11.1g/dL), which is probably due to his underlying chronic disease.

Warfarin is a criterion standard treatment for APS patients with prior thromboembolic events. It is used as a secondary antithrombotic prophylaxis with a target INR of 2.0–3.0 and should be taken lifelong. The anticoagulant effect of warfarin can be monitored using INR.

Conclusions

Antiphospholipid syndrome (APS) is a complex autoimmune disorder marked by thromboembolic events and pregnancy complications, associated with specific autoantibodies. Despite the evolution of classification criteria from the initial Sapporo Criteria in 1999 to the latest ACR/EULAR Criteria in 2023, diagnosing APS remains challenging due to its heterogeneity. APS requires lifelong anticoagulation therapy with warfarin to prevent further thromboembolic events. Monitoring warfarin therapy using INR in the background of APS may be complicated by LA because LA can interfere with routine coagulation tests. Our case highlights the impact of LA on PT/INR measurements and the importance of understanding the limitations of the tests available. We had to change to a tissue-derived PT reagent to allow INR to be used to monitor the anticoagulant effect in this patient. Unfortunately, the patient was lost to follow-up after 1 year. Nevertheless, this case illustrates how extensive troubleshooting can be to ensure a reliable result.

References:

1.. Knight JS, Branch DW, Ortel TL, Antiphospholipid syndrome: Advances in diagnosis, pathogenesis, and management: BMJ, 2023; 380; e069717

2.. Devreese KMJ, de Groot PG, de Laat B, Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis: Update of the guidelines for lupus anticoagulant detection and interpretation: J Thromb Haemost, 2020; 18(11); 2828-39

3.. Barbhaiya M, Zuily S, Naden R, 2023 ACR/EULAR antiphospholipid syndrome classification criteria.: Ann Rheum Dis, 2023; 82(10); 1258-70

4.. Yang Y, Jiang H, Tang Z, Assessment of the 2023 ACR/EULAR antiphospholipid syndrome classification criteria in a Chinese cohort: Impact on clinical practice: J Autoimmun, 2024; 146; 103237

5.. Tektonidou MG, Andreoli L, Limper M, EULAR recommendations for the management of antiphospholipid syndrome in adults.: Ann Rheum Dis, 2019; 78(10); 1296-304

6.. Pérez ML, Laso RV, Velasco-Rodríguez D, Lupus anticoagulant-hypoprothrombinemia syndrome: A cerebral bleeding case report as systemic lupus erythematosus debut: Reumatol Clin (Engl Ed), 2023; 19(4); 223-27

7.. Ramezanpour N, Zaker F, Biswas A, Dorgalaleh A, Inhibitor in congenital factor VII deficiency; A rare but serious therapeutic challenge – a systematic literature review: J Clin Med, 2021; 10(2); 211

8.. Song Z, Wu H, Cao H, Routine coagulation test abnormalities caused by rivaroxaban: A case report: Medicine (Baltimore), 2018; 97(45); e13104

9.. Douxfils J, Mullier F, Loosen C, Assessment of the impact of rivaroxaban on coagulation assays: Laboratory recommendations for the monitoring of rivaroxaban and review of the literature.: Thromb Res, 2012; 130(6); 956-66

10.. Tripodi A, de Laat B, Wahl D, Monitoring patients with the lupus anticoagulant while treated with vitamin K antagonists: Communication from the SSC of the ISTH: J Thromb Haemost, 2016; 14(11); 2304-7

11.. Smith S, Comp P, Morrissey J, Phospholipid composition controls thromboplastin sensitivity to individual clotting factors: J Thromb Haemost, 2006; 4(4); 820-27

12.. Gehlen R, Moesbergen RG, Bai C, Interference of lupus anticoagulant causing antiprothrombin and anti-beta-2-glycoprotein I antibodies on international normalized ratio measurements: Comparative analysis of international normalized ratio methods: Res Pract Thromb Haemost, 2024; 8(5); 102470

13.. Huseynov A, Haselmann V, Kittel M, Lupus antibody mimicking reduced plasmatic coagulation in a patient with atrial fibrillation and ischemic stroke: Front Neurol, 2020; 11; 896

14.. Tripodi A, Chantarangkul V, Clerici M, Laboratory control of oral anticoagulant treatment by the INR system in patients with the antiphospholipid syndrome and lupus anticoagulant. Results of a collaborative study involving nine commercial thromboplastins.: Br J Haematol, 2001; 115(3); 672-78

15.. Favaloro EJ, Pasalic L, Lupus anticoagulant testing during anticoagulation, including direct oral anticoagulants: Res Pract Thromb Haemost, 2022; 6(2); e12676

16.. He XY, Bai Y, Acute thrombocytopenia after anticoagulation with rivaroxaban: A case report.: World J Clin Cases, 2020; 8(5); 928-31

17.. Tomasello R, Giordano G, Romano F, Immune thrombocytopenia in antiphospholipid syndrome: Is it primary or secondary?: Biomedicines, 2021; 9(9); 1170

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American Journal of Case Reports eISSN: 1941-5923
American Journal of Case Reports eISSN: 1941-5923