Case Report: Abnormal Fluctuation of International Normalized Ratio Due to Laboratory Errors and Drug Interactions

Abstract

Background: Warfarin, a widely-used anticoagulant for thrombotic event management, can lead to overanticoagulation due to various factors. In patients with markedly elevated international normalized ratio (INR) on warfarin, practitioner often focus on medication changes and dietary influences, but inadvertently overlook the coagulation function report’s credibility.

Case information: We present a patient whose INR rapidly exceeded the detectable range after warfarin and ceftriaxone/tazobactam use, with subsequent challenges in correction. The patient experienced nosebleeds and extensive subcutaneous bleeding, and INR gradually returned to normal after multiple interventions. Retrospectively, the patient adjusted warfarin dosage without monitoring INR, posing overdose risk. The mismatch between INR and activated partial thromboplastin time (APTT) suggests possible laboratory errors contributing to the rapid INR increase. Additionally, potential warfarin-ceftriaxone/tazobactam interactions could cause recurring mild INR increases.

Conclusion: Evaluating coagulation function in warfarin patients necessitates assessing report credibility. INR-APTT correlation effectively confirms reliability. Healthcare professionals must be aware of the report’s credibility and this specific interaction, particularly when managing elderly patients with multiple complications and medications. Considering report credibility, close patient monitoring, and avoiding potential interacting drugs can minimize adverse event risk.

Note:

Funding Information: We would like to clarify that this research did not receive any external funding or financial support. It was conducted as part of routine clinical and academic activities without specific grant or sponsorship.

Conflict of Interests: None to declare

Ethical Approval: The studies were reviewed and approved by Medical Ethics Committee of the First Affiliated Hospital of Guangzhou University of Chinese Medicine. Seven months after the patient was released from the hospital, we contacted the patient for a followup and obtained informed consent.

Keywords: case report, coagulopathy, warfarin, antibiotic, laboratory errors