To evaluate the influence of age, sex and ABO blood group on the activated partial thromboplastin time (APTT), we performed this test in 642 preoperative ambulant adult subjects. There was a significant negative correlation (R = 0.31, p < 0.001) between age and APTT. Sex and ABO blood group had a significant influence on APTT, with lower mean in females (30.9 s) and non-0 subjects (30.7 s) than in males (31.6 s) and·subjects (32.0 s) (p = 0.015 and < 0.001, respectively). The largest difference between the upper cut-off values of APTT determined in patient subgroups defined on age, sex and ABO blood group is observed for non-O females over 40 years (36.9 s) and·males under 40 years (41.1 s). These results emphasize the laboratory’s difficulties to define valid APTT normal range and thus to detect true mild coagulation disorders in preoperative asymptomatic patients.

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