# Discrepancy between international normalized ratio measurements in a heterozygous carrier of F10:p.Gly244Arg with recurrent venous thromboembolism: a case report

## TL;DR

A patient with a F10 gene variant had inconsistent INR measurements due to different thromboplastin types, highlighting the need to consider F10 variants in anticoagulant monitoring.

## Contribution

This case report shows that F10:p.Gly244Arg heterozygosity can cause INR discrepancies with different thromboplastins.

## Key findings

- A patient with F10:p.Gly244Arg had different INR values when using rabbit versus human thromboplastin.
- Genetic variants in F10 may affect INR measurements similarly to F7 variants.
- Discrepant INR results should prompt testing for F10 and F7 genetic variants.

## Abstract

The international normalized ratio (INR) is designed to monitor vitamin K antagonist (VKA) treatment. Before patients start a self-managing VKA program, parallel measurements are conducted to compare point-of-care testing (POCT) INR with venous INR samples. Previously, genetic variants in F7 have shown discrepancies in INR measurements when thromboplastins from different species were used. It is unknown whether genetic variants in F10 affect INR measured with thromboplastins from different species.

Does F10:p.Gly244Arg heterozygosity affects the INR when measured using rabbit compared with human thromboplastin?

A patient self-managing warfarin treatment had a recurrent venous thromboembolism during VKA treatment. The POCT therapeutic range was low (ie, 1.6-2.4) based on parallel measurements of POCT INR (human thromboplastin) and venous INR (rabbit thromboplastin). Subsequently, it was noted that the patient had a spontaneous increase in INR (1.3), and the patient was found to be a heterozygous carrier of F10:p.Gly244Arg.

Genetic variants in F10 may also interfere with INR or prothrombin time measurements when different thromboplastins are used. This case illustrates that discrepancies in INR measurements with different thromboplastins should prompt consideration of genetic variants in F10 and F7 to ensure sufficient anticoagulant VKA treatment.

•Warfarin treatment can be monitored by a point-of-care INR test.•Discrepancies in INR measurements have previously been observed in carriers of genetic variants in F7.•Here, a heterozygote carrier of F10:p.Gly244Arg had different INR values depending on the thromboplastin used.•Genetic variants in F10 should also be considered when the INR result depends on the thromboplastin used.

Warfarin treatment can be monitored by a point-of-care INR test.

Discrepancies in INR measurements have previously been observed in carriers of genetic variants in F7.

Here, a heterozygote carrier of F10:p.Gly244Arg had different INR values depending on the thromboplastin used.

Genetic variants in F10 should also be considered when the INR result depends on the thromboplastin used.