A client is at risk for pulmonary embolism and is on anticoagulant therapy with warfarin (Coumadin). The client’s prothrombin time is 20 seconds, with a control of 11 seconds. The nurse assesses that this result is:
A. The same as the client’s own baseline level.
B. Lower than the needed therapeutic level.
C. Within the therapeutic range.
D. Higher than the therapeutic range.
Correct Answer: C. Within the therapeutic range.
The therapeutic range for prothrombin time is 1.5 to 2 times the control for clients at risk for thrombus. Based on the client’s control value, the therapeutic range for this individual would be 16.5 to 22 seconds. Therefore the result is within the therapeutic range. PT measures the time, in seconds, for plasma to clot after adding thromboplastin, (a mixture of tissue factor, calcium, and phospholipid) to a patient’s plasma sample.
Option A: Many different preparations of thromboplastin reagents are available which can give different PT results even when using the same plasma. Due to this variability, the World Health Organization (WHO) introduced the international normalized ratio (INR) and has become the standard reporting format for PT results.
Option B: The reference ranges for PT vary by laboratory since different facilities use reagents or instruments. However, in most laboratories, the normal range for PT is 10 to 13 seconds. The normal INR for a healthy individual is 1.1 or below, and the therapeutic range for most patients on VKAs is an INR of 2.0 to 3.0.
Option D: An increased PT/INR for patients on VKAs may suggest a super-therapeutic level and will require medication dose adjustments to prevent bleeding. As the use of VKAs increases, it is vital to educate patients on the importance of routine monitoring of PT/INR. Proper monitoring will allow for medication adjustments and prevention of adverse events.
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