Platelet count is not the primary diagnostic test used to monitor the therapy’s effect of warfarin. Platelets are involved in the clotting process, but warfarin specifically works by inhibiting the synthesis of vitamin K-dependent clotting factors, which does not directly involve platelets.

Choice B rationale

The white blood cell count (WBC) is not used to monitor the effect of warfarin therapy. WBC is typically used to monitor for infection or inflammation, not the coagulation status of a patient.

Choice C rationale

Prothrombin time (PT) is the correct answer. Warfarin therapy is monitored using the PT, which is reported as the International Normalized Ratio (INR). Warfarin inhibits the synthesis of vitamin K-dependent clotting factors, which include Factors II, VII, IX, and X, and Proteins C and S. The PT/INR is sensitive to changes in these factors. An elevated INR indicates a higher risk of bleeding, while a lower INR suggests a higher risk of clotting.

Choice D rationale

Activated partial thromboplastin time (aPTT) is not typically used to monitor warfarin therapy. The aPTT test evaluates the intrinsic and common pathways of coagulation, which includes factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen). Warfarin affects the extrinsic pathway and common pathway, not the intrinsic pathway. Therefore, aPTT is not the best test to monitor the effects of warfarin.

Choice A rationale

Respiratory alkalosis is typically associated with hyperventilation, which can occur in conditions such as anxiety, fever, or certain lung diseases. However, it is less likely in a patient who is nauseous and vomiting.

Choice B rationale

Metabolic alkalosis is a condition that can occur due to the loss of acid from the body, which can happen when a patient is vomiting. When a person vomits, they lose stomach acid (hydrochloric acid), and this can disrupt the acid-base balance in the body, leading to metabolic alkalosis.

Choice C rationale

Metabolic acidosis is typically associated with conditions that cause the accumulation of acid in the body or the loss of bicarbonate, such as kidney disease, lactic acidosis, or certain poisonings. It is less likely in a patient who is nauseous and vomiting.

Choice D rationale

Respiratory acidosis is typically associated with conditions that cause an inability to remove enough carbon dioxide from the body, such as chronic obstructive pulmonary disease (COPD) or airway obstruction. It is less likely in a patient who is nauseous and vomiting.