Author Question: A patient is stabilized on warfarin therapy and being monitored using the prothrombin time (PT) ... (Read 118 times)

CQXA · **on:** Jun 25, 2018

A patient is stabilized on warfarin therapy and being monitored using the prothrombin time (PT) followed by calculation of the international normalized ratio (INR). The formula for calculating the INR is:

INR = (PTpatient/PTnormal)ISI (where ISI = international sensitivity index)

What is used for the PTnormal?

a. Arithmetic mean PT for the control
b. Geometric mean PT for the reference population
c. Arithmetic mean PT as found in a standard reference textbook
d. Geometric mean PT reported by the manufacturer of the PT reagent being used

Question 2

Once a patient is stabilized on warfarin therapy, how often should he or she be monitored?

a. Once every 6 months
b. Once every week
c. Once a year
d. Once a month

Expo · **Reply #1 on:** Jun 25, 2018

Answer to Question 1

ANS: B
The PTnormal is the geometric mean for the PT reference interval determined by the clinical laboratory scientists in the laboratory where the testing is being performed. Using the wrong value in this calculation has led to major reporting errors that have resulted in bad patient outcomes.

Answer to Question 2

ANS: D
Once a patient is stabilized on warfarin therapy, monitoring should continue monthly until therapy is complete. Changes in diet, metabolism, renal function, other drugs being taken, as well as additional factors all change the response to warfarin and may require making dosage adjustments.