Question 1

What is the most common cause of a high INR in a stable patient?

Accepted Answer

Drug interactions (new antibiotics, antifungals, amiodarone, NSAIDs), dietary changes (reduced vitamin K intake), acute illness (reduced warfarin clearance and catabolism), or unintentional warfarin dose duplication.

Question 2

How should I manage a single subtherapeutic INR (1.5–1.9)?

Accepted Answer

If the patient has no recent thromboembolism and no mechanical valve, a single subtherapeutic INR does not require bridging with LMWH. The warfarin dose should be increased per the local nomogram and the INR rechecked in 7–14 days.

Question 3

Is INR reliable in patients with lupus anticoagulant?

Accepted Answer

Lupus anticoagulant can interfere with PT reagents and cause falsely elevated INR. Alternative monitoring strategies (chromogenic factor X assay or serial factor II levels) may be needed to guide warfarin dosing.

Question 4

Can I use INR for DOAC monitoring?

Accepted Answer

No. DOACs (dabigatran, rivaroxaban, apixaban, edoxaban) have predictable pharmacokinetics and do not require routine monitoring. The INR is not sensitive or specific for any DOAC. Specific anti-Xa or dilute thrombin time assays are used when DOAC level measurement is needed.