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J Thromb Thrombolysis. 2003 Jun;15(3):213-6.

Quality assessment of anticoagulation dose management: comparative evaluation of measures of time-in-therapeutic range.

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Departments of Medicine & Pharmacy, Boston University Medical Center, 88 East Newton Street, Boston, MA 02118, USA.



The results of clinical trials often hinge on the quality of oral anticoagulation management, yet the quality of such management is frequently not mentioned or measured. Time-in-therapeutic range (TTR) is one measure of quality of anticoagulation dose management, but various methodologies exist for measuring TTR.


This study was initiated to compare three commonly used methodologies for measuring TTR to see how they compare within the same cohort of patients.


Three common methodologies of calculating time-in-therapeutic range were analyzed retrospectively in a cohort of patients over six two-month intervals. Additional analysis was performed for three and six-month intervals. The methodologies included fraction of INRs in range; cross-section of the files; and linear interpolation.


Fraction of the INRs in range and cross-section of the files methodologies gave similar results, while linear interpolation yielded significantly shorter time-in-range for the two-month, three-month, and six-month intervals measured. The advantages and disadvantages of each methodology are discussed.


The decision of which method to use should be based on clinic size, information desired, and clinic resources for ease of applying either of the methods in clinical practice. Each of these methodologies has their limitations and the question remains as to which method best reflects the quality of anticoagulation management. Regardless of these limitations, investigators are urged to employ at least one method of measuring the quality of oral anticoagulation management so as to better assess the validity of the clinical outcomes.

[Indexed for MEDLINE]

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