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Case Reports
. 2025 Mar 19:9:a25425358.
doi: 10.1055/a-2542-5358. eCollection 2025.

Problem Solved? An Individual Ratio between Point-of-Care and Venous International Normalized Ratio Values in Two Patients with Antiphospholipid Syndrome: Two Case Reports

Bettina C Geertsema-Hoeve  1 , Massimo Radin  2 , Savino Sciascia  2 , Rolf T Urbanus  3 , Albert Huisman  3 , Josine Borgsteede-de Wilde  1 , Maarten Limper  1
Affiliations
Case Reports

Problem Solved? An Individual Ratio between Point-of-Care and Venous International Normalized Ratio Values in Two Patients with Antiphospholipid Syndrome: Two Case Reports

Bettina C Geertsema-Hoeve et al. TH Open. .

Abstract

Antiphospholipid syndrome (APS) is a rare autoimmune disorder characterized by thromboembolic and obstetric complications in the presence of persistent antiphospholipid antibodies (aPL). Treatment aims to prevent recurrent thrombosis, primarily using anticoagulation therapy with vitamin K antagonists (VKA). Monitoring of VKA therapy relies on the International Normalized Ratio (INR), which can be assessed using point-of-care testing (POCT). However, in a subset of APS patients with a high-risk aPL profile, the POCT-INR is falsely elevated, which might lead to underdosing of VKA and subsequent high risk of recurrent thrombosis. This case report describes two female patients with triple-positive thrombotic APS receiving VKA therapy. Both patients underwent biweekly paired INR measurements via POCT-INR and venous INR methods. Despite significant discrepancies, a strong individual linear correlation was observed: r = 0.77 (95% confidence interval [CI]: 0.54-0.99, p < 0.001) and r = 0.93 (95% CI: 0.88-0.97, p < 0.001), respectively. These findings suggest that individualized correction factors could be developed to improve the accuracy of POCT-INR measurements, thereby optimizing VKA dosing in these patients.

Keywords: International Normalized Ratio; antiphospholipid syndrome; case report; point-of-care testing; vitamin-k antagonists.

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Conflict of interest statement

Conflict of Interest None declared.

Figures

Fig. 1
Fig. 1
Correlation between POCT-INR and venous INR values in two patients with antiphospholipid syndrome. The results of serial paired measurements of POCT-INR and venous INR, measured by Owren's method. Although the underlying mathematical formulas differ, both patients exhibited a linear correlation between POCT-INR and venous INR. Y formula is the formula with which a venous INR can be calculated from a POCT-INR value. Pearson's correlation for patient 1 was r  = 0.77 ( p  < 0.001), Pearson's correlation for patient 2 was r  = 0.93 ( p  < 0.001). INR, International Normalized Ratio; POCT, point-of-care testing.
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References

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