A nurse is reporting a client’s laboratory tests to the provider to obtain a prescription for the client’s daily warfarin.

Which of the following laboratory tests should the nurse plan to report to obtain the prescription for the warfarin?

The correct answer is choice A. INR.

Warfarin is a vitamin K antagonist that inhibits the synthesis of factors II, VII, IX, and X in the liver.

These factors are part of the extrinsic and common pathways of coagulation, which are measured by the prothrombin time (PT) and the international normalized ratio (INR).

The INR is a standardized way of reporting the PT that accounts for the variability of different reagents and instruments.

The INR is used to monitor the therapeutic effect of warfarin and to adjust the dose accordingly.

The target INR range depends on the indication for warfarin, but it is usually between 2 and 3 for most conditions.

Choice B is wrong because fibrinogen level is not affected by warfarin.

Fibrinogen is a precursor of fibrin, which forms the final step of the coagulation cascade.

Fibrinogen level can be decreased in conditions such as disseminated intravascular coagulation (DIC), liver disease, or severe bleeding. Choice C is wrong because aPTT is not affected by warfarin.

aPTT measures the intrinsic and common pathways of coagulation, which are mainly dependent on factors VIII, IX, XI, and XII.

These factors are not inhibited by warfarin.

aPTT is used to monitor the effect of heparin, a direct antithrombin agent that inhibits thrombin and factor Xa.

Choice D is wrong because platelet count is not affected by warfarin.

Platelets are cell fragments that adhere to damaged blood vessels and form aggregates to initiate hemostasis.

Platelet count can be decreased in conditions such as immune thrombocytopenia (ITP), heparin-induced thrombocytopenia (HIT), or bone marrow suppression.

Normal ranges:

• INR: 0.8-1.2
• Fibrinogen: 200-400 mg/dL
• aPTT: 25-35 seconds
• Platelet count: 150-450 x 10^9/L References: