Is the time in therapeutic range on coumarins predicted by previous time in therapeutic range?

Abstract

Background The benefit of vitamin K antagonists depends on the time within the therapeutic range (TTR). A patient’s previous TTR could be a factor in the decision to change the anticoagulation regimen. However, the predictive value of a previous TTR for a future TTR is not well established, nor is it clear which TTR should prompt action. Objectives To investigate the predictive performance of a TTR and identify a threshold below which no recovery of TTR should be expected. Patients/Methods From 18 031 patients who used acenocoumarol in a first‐line anticoagulation clinic, a TTR was calculated over multiple periods of 90, 180, and 365 days each. We assessed the correlation between baseline and later TTR and the separation between groups by quintile of baseline TTR. We describe the proportion of patients who obtain a TTR≥ 70% conditional on baseline TTR. Results The correlation between baseline and later TTR was 0.25 (95% confidence interval [CI], 0.24‐0.26), 0.27 (95% CI, 0.26‐0.28) and 0.34 (95% CI, 0.32‐0.35) for analyses over 90, 180, and 365 days. Corresponding c statistics for discrimination by baseline group were 0.60, 0.61, and 0.63. The probability to obtain a TTR ≥70% increased with baseline TTR: from 42% with a baseline TTR of 50%‐65% when TTR was 100% (TTR calculated over 180 days). Conclusions We conclude that a current TTR hardly predicts a future TTR. Physicians and patients should deliberate together which probabilities to accept, take measures to improve TTR, and consider potential alternatives.

The quality of pharmacist-led community warfarin management across 2 provinces in Canada: A cross-sectional observational study

“…While this is a logical explanation, a study including more than 18,000 patients suggested that past INR stability does not predict future INR control. 14 Our data suggested no difference between the quality of warfarin management between types of ambulatory practice sites. This provides support that with standardized training, pharmacist-led warfarin management using point-of-care INR testing and decision-support software can be effective regardless of the setting.…”

“…While this is a logical explanation, a study including more than 18,000 patients suggested that past INR stability does not predict future INR control. 14 …”

Effect of switching from acenocoumarol to phenprocoumon on time in therapeutic range and INR variability: A cohort study

“…A Polish study, confined to younger patients with arbitrarily defined "unstable anticoagulation", found a marked increase in TTR after the switch [18]. Because both studies lacked a control group, and TTR is not stable over time [19], their results could be distorted by "regression" to the mean.…”