Control of warfarin treatment in patients with antiphospholipid syndrome and falsely high INR at point-of-care-testing
Jørn Dalsgaard Nielsen a), Thomas Steffen Hermann a), Konstantinos Dimopoulos b), Anne Storgaard Nørskov c) d)
a) Center of Excellence for Anticoagulant Treatment, Department of Cardiology, Copenhagen University Hospital – Bispebjerg and Frederiksberg, Denmark
b) Department of Clinical Biochemistry, Copenhagen University Hospital – Bispebjerg and Frederiksberg, Denmark
c) Research Division, Department of Cardiology, Copenhagen University Hospital – Bispebjerg and Frederiksberg, Denmark
d) Department of Cardiology, Copenhagen University Hospital – North Zealand, Hillerød, Denmark
Abstract
Background
The standard of care for thrombotic antiphospholipid syndrome (APS) is anticoagulation with vitamin K antagonists (VKA). Several studies have indicated that lupus anticoagulant (LA) can interfere with the international normalized ratio (INR) results obtained by point-of-care testing (POCT) devices. A subset of patients with APS has clinically significant systematic differences between POCT INR and plasma INR (P-INR) measured in the hospital laboratory.
Objectives
We aimed to investigate a potential correlation between POCT INR (CoaguChek, Roche Diagnostics) and P-INR in these patients.
Materials and methods
In our anticoagulation clinic, we compared 363 paired CoaguChek-INR (CC-INR) with P-INR results using Owren’s method from 37 patients with APS receiving self-managed VKA. Each patient had a minimum of three paired measurements of CC-INR and P-INR and a median CC-INR/P-INR ratio > 1.20.
Results
In all patients, we found a strong linear correlation between CC-INR and P-INR (median R2: 0.89; IQR: 0.78–0.94). Each patient had their own characteristic regression line from which CC-INR could be converted to P-INR. Thirty-four patients continued with self-managed treatment and the use of a conversion table. However, 3 patients had to switch to INR control in the anticoagulation clinic, as the upper limit of their therapeutic CC-INR interval exceeded the maximum (INR: 8.0) on their CoaguChek device.
Conclusions
In a subset of patients with APS who, during self-managed VKA therapy, had persistently higher POCT INR than P-INR, the majority could continue with self-managed therapy using a conversion table, as the falsely elevated POCT INR values were linearly correlated to P-INR.