5 Laboratory Monitoring of Antithrombotic Therapy Free Online FlashCards

Which test monitors warfarin therapy?

Warfarin is monitored with prothrombin time reported as the international normalized ratio (PT/INR).

How should a warfarin INR be interpreted?

The prescribed target depends on the reason for treatment. A common target for many indications is 2.0–3.0; a high INR generally means greater anticoagulant effect, while a low INR may mean inadequate protection from clotting.

Which tests can monitor intravenous unfractionated heparin?

Unfractionated heparin is commonly monitored with aPTT or a heparin-calibrated anti-factor Xa assay, following the local protocol and assay-specific therapeutic range.

What can be considered when aPTT is unreliable during heparin treatment?

Consider whether aPTT is reliable for the patient; a baseline abnormality or lupus anticoagulant can make it unreliable. Anti-factor Xa monitoring may be preferred.

Which blood counts are important during heparin treatment besides the anticoagulation assay?

Follow the platelet count and hemoglobin/hematocrit, and investigate evidence of blood loss.

What can a substantial platelet fall during heparin exposure indicate?

A substantial platelet fall during heparin exposure can signal heparin-induced thrombocytopenia (HIT), a prothrombotic adverse reaction. Interpret the trend and clinical context, not just one value.

Is routine laboratory dose adjustment usually needed for low-molecular-weight heparin?

Routine anti-Xa monitoring is generally unnecessary for most patients on standard low-molecular-weight heparin therapy; selected cases may need anti-Xa testing. The aPTT is not a suitable measure of its effect.

Do normal PT/INR and aPTT results rule out an apixaban effect?

No. Routine PT/INR and aPTT are not reliable measures of apixaban activity, and normal results do not rule out a clinically relevant drug level. If testing is needed, use an appropriately calibrated apixaban anti-factor Xa assay when available.

Which tests can assess dabigatran effect when testing is needed?

A dilute thrombin time or ecarin-based assay can measure dabigatran effect when testing is clinically necessary; availability varies.

What does thrombin time show about dabigatran?

Thrombin time is highly sensitive to dabigatran: a normal result can help exclude a clinically relevant level, but a prolonged result alone does not quantify how much clinically important drug remains.

Can INR determine the intensity of rivaroxaban treatment?

No. PT changes with factor Xa inhibitors depend on the reagent, and INR is standardized for warfarin, not DOAC intensity. If a rivaroxaban level is needed, use a drug-calibrated anti-factor Xa assay when available.

Do routine coagulation tests measure aspirin or clopidogrel effects?

No routine coagulation test, including PT/INR or aPTT, measures the intended platelet inhibition from aspirin or clopidogrel. Platelet-function testing is reserved for selected situations.