PB0416 - Falsely elevated PT-INR results measured with Quick point-of-care methods and Quick laboratory method in patients with antiphospholipid syndrome.

Sunday, July 10, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Presenting Author(s)

Ann Helen Kristoffersen, MD, PhD

MD, PhD
Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
Bergen, Hordaland, Norway

Co-Author(s)

Tomas L. Lindahl, MD, PhD

Director of Reseach, professor
Linköping University, Linköping, Sweden
Linköping, Ostergotlands Lan, Sweden
HA

Hege Alvheim

Biomedical Scientist
Noklus, Haraldsplass Deaconess Hospital, Bergen, Norway
Bergen, Hordaland, Norway
AS

Anne Stavelin

Biomedical Scientist, PhD
Noklus, Haraldsplass Deaconess Hospital, Bergen, Norway
Bergen, Hordaland, Norway
MH

Marit Hellum

Researcher, PhD
Institute of Clinical Medicine, University of Oslo, Oslo, Norway
Oslo, Oslo, Norway
U�

Una Ørvim Sølvik

Associate Professor
Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway
Bergen, Hordaland, Norway
TG

Thue Geir

Professor, MD
Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway
Bergen, Hordaland, Norway
EB

Ellen Brodin

MD, PhD
Akershus University Hospital, Lørenskog, Norway
Lørenskog, Akershus, Norway
SS

Sverre Sandberg

Professor, MD
Noklus, Haraldsplass Deaconess Hospital, Department of Global Public Health and Primary Care, University of Bergen and Norwegian porphyria centre, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
Bergen, Hordaland, Norway
CH

Carola Elisabeth Henriksson, MD

MD, Associate professor
Institute of Clinical Medicine, University of Oslo, Oslo, Norway
Oslo, Oslo, Norway

Background: Falsely elevated PT-INR results are reported in some patients with antiphospholipid syndrome (APS), but it is not clear which methods and patients that are affected.

Aims: To study which PT-INR methods are most prone to interference, and if antibody profiles in APS-patients may explain such interference.

Methods: Blood was drawn from 29 controls and 21 APS-patients for 1 - 4 times per participant. PT-INR was analysed with five different point-of-care (POC) instruments (three Quick methods (capillary blood, no dilution) and two Owren methods (1:21 and 1:6 dilution)); one Quick laboratory method (1:3 dilution), and one Owren laboratory method (1:21 dilution, used as the reference PT-INR method). Chromogenic factor X was analysed as an alternative monitoring method. To establish antibody profiles, lupus anticoagulant, anti-cardiolipin, anti-beta-2-glycoprotein I, anti-phosphatidylserine/prothrombin (anti-PS/PT) and anti-beta-2-glycoprotein I domain I (anti-B2GPI-DI) antibodies were analysed.

Results: Falsely elevated PT-INR results (>20% PT-INR difference compared to the reference method) were seen in up to five of 21 APS-patients with the Quick methods (both POC instruments and laboratory method), but not with POC Owren methods (Figure 1). The five APS-patients were tetra-positive (including anti-PS/PT antibodies) with an anti-B2GPI-DI antibody titer above 500 U/mL. Falsely elevated PT-INR and high titer antiphospholipid antibodies were seen consistently over time. Tetra-positivity was also seen in six of 21 APS-patients without falsely elevated PT-INR, but their anti-B2GPI-DI antibody titer was either normal ( < 30 U/mL, n=2) or less than 180 U/mL (n=4).

Conclusion(s): PT-INR POC Quick methods with no dilution of patient samples have the highest risk of falsely elevated PT-INR in APS-patients, but PT-INR Quick laboratory methods may also give falsely elevated results in some of these patients. Very high anti-B2GPI-DI antibody titers were only seen in the five APS-patients with falsely elevated PT-INR, and in such patients, Owren methods should be used.