INFLUENCE OF GENDER, AGE AND SAMPLING TIME ON PLASMA FIBRINOLYTIC VARIABLES AND FIBRINOGEN - A POPULATION STUDY

Reference data are provided for tissue plasminogen activator (t-PA) activity, t-PA antigen levels, plasminogen activator inhibitor type 1 (PAI-1) activity and fibrinogen levels in plasma. The data are from a population-based sample of 1288 healthy 25 to 64-year-old men and women who were not taking any medication. Time of sampling influenced the measurements in that, from 07:00 to 14:00 t-PA activity rose, t-PA antigen levels and PAI-1 activity declined, whereas plasma fibrinogen levels remained unchanged. Age had little influence on t-PA activity or PAI-1 activity, although t-PA antigen levels correlated with increasing age (r=0.26 and 0.34, in men and women, respectively). Fibrinogen levels also correlated with age (r=0.29 in both sexes). In the 45 to 54-year age group, t-PA activity was significantly lower (p<0.001) and PAI-1 activity significantly greater (p < 0.01) in men than in women; otherwise there were no gender differences in t-PA and PAI-1 activities. t-PA antigen levels were consistently greater in men up to the age of 55. Fibrinogen levels were greater in women in the youngest and oldest age group. The strongest interrelations between the fibrinolytic variables were observed between t-PA and PAI-1 activities (r=-0.73 in men, -0.59 in women, p<0.001) and between PAI-1 activity and t-PA antigen levels (r=0.40 in men, 0.37 in women, p<0.001). This first population-based description of fibrinolytic parameters, including t-PA activity, in healthy middle-aged people shows that timing of blood sampling should be standardized and that reference data must be age- and sex-specific. In the assessment of fibrinolytic function, measurements of t-PA antigen levels seem to add little to determinations of t-PA and PAI-1 activities.