Background and objective. High plasminogen activator inhibitor type 1 (PAI‐1) activity is associated with inflammatory reactions and insulin resistance, but it is unclear what regulates PAI‐1 activity at the low end. The purpose of this study was to investigate if patients with low PAI‐1 activity have a lack of inflammatory response or a low insulin level.
Design. Retrospective cohort study with internal controls.
Subjects. Sixty‐three patients referred for investigation of bleeding tendency and with low PAI‐1 activity were compared with 118 patients with normal or high PAI‐1 activity.
Outcome. Levels of C‐peptide, proinsulin, high‐sensitivity C‐reactive protein (hs‐CRP) and interleukin‐6 (IL‐6). Adjustments were made for body mass index (BMI), oral oestrogens and age. Low PAI‐1 activity was defined as less than 1 U mL−1.
Results. Body mass index in the low normal range, oral oestrogens, young age and low C‐peptide were significantly associated with low PAI‐1 activity and there was a trend for association with IL‐6 in univariable analysis. The effect of age disappeared after correction for oral oestrogens and the effect of C‐peptide and IL‐6 disappeared after further adjustments. Low BMI remained as the strongest predictor of low PAI‐1 activity.
Conclusion. Patients with bleeding tendency and low PAI‐1 activity have inflammatory and insulin profiles similar to those with normal or high PAI‐1, whereas BMI seems to be the most important determinant.