BACKGROUND: Dabigatran has demonstrated promising results for the prevention of 
strokes in patients with non-valvular atrial fibrillation (NVAF). However, there 
have been episodes of major bleeding, especially in elderly patients or those 
with renal dysfunction. The purpose of this study was to retrospectively examine 
the relationship between the bleeding events and activated partial 
thromboplastin time (APTT) values under dabigatran usage in the everyday 
clinical practice. Moreover, we investigated which factors would contribute to 
the APTT values.
METHODS AND RESULTS: A total of 139 NVAF patients (112 men, 65 ± 11 years) were 
included. We evaluated the influence of the putative etiological variables and 
the bleeding score, HAS-BLED score, on APTT values: age greater than 70 years, 
renal function, gender, dose of dabigatran, and the concomitant prescription of 
a P-glycoprotein inhibitor. There were 50 patients with an age of ≥ 70 years 
(36.0%). A P-glycoprotein inhibitor was administered in 18 patients. During the 
observation period (median 120 days) there was 1 episode of asymptomatic 
cerebral infarction. There were no intrinsic major bleeding events, however, 11 
patients had minor hemorrhagic events. The results of the APTT measurements 
exhibited a variety of values both among inter- and intra-individuals. On 
multivariable analysis, significant associations were found between the 
following risk factors and the APTT values: creatinine clearance, dose of 
dabigatran, and concomitant use of a P-glycoprotein inhibitor. The minor 
bleeding events did not correlate with the APTT values, nor HAS-BLED score.
CONCLUSIONS: The APTT values became prolonged under dabigatran usage and 
exhibited a remarkable diversity. Although major bleeding did not occur unless 
APTT was prolonged excessively, minor bleeding arose irrespective of the APTT 
values even within the range of the APTT values not exceeding 80s.