Plasminogen Activator Inhibitor Type 1 Deficiency

Laboratory Evaluation

Common tests of coagulation including the PT, aPTT and TCT are normal. Euglobin clot lysis time (ECLT) is short. The ECLT and whole blood clotting assays such as the thromboelastogram are helpful in diagnosis of hyperfibrinolytic states but are insufficient to confirm PAI-1 deficiency where the diagnosis is based on the measurement of antigenic [enzyme-linked immunosorbent assay (ELISA)] and functional (chromogenic test) PAI-1.

Iwaki et al. (2017) are in the process of developing a highly sensitive human PAI-1 assay using AlphaLISA® technology (PerkinElmer Japan, Yokohama, Japan). Anti-human PAI-1 rabbit polyclonal antibody coated AlphaLISA® Acceptor beads and biotinylated antihuman PAI-1 rabbit polyclonal antibody are mixed with samples or unglycosilated recombinant human PAI-1 as a standard. Then, streptavidin-coated AlphaLISA Donor beads are added to the mixture. This test was used for the first time in the 70-year old patient with a dysfunctional protein described above. This new test revealed patient’s PAI-1 plasma level was 120 pg/ml, which could not be detected by conventional assays.63

PAI-1 antigen assays lack the ability to detect qualitative defects and activity assays lack the appropriate sensitivity at very low levels to differentiate low normal from a true deficiency state. The majority of PAI-1 tests performed are used to detect enhanced activity, not a deficiency state.  Often times, an activity level of zero is reported to be within the normal limits of assay detection.49

PAI-1 also has diurnal variation with higher values observed in the morning and nadir values in the afternoon.73. This variance may be regulated by proteins CLOCK:ARNTL1 and CLOCK:ARNTL2 which bind to the SERPINE1 promoter and up regulate  its expression. These proteins are contained in ARNTL locus of the Chromosome 11p15.2.74,75

Additionally, it has been reported that PAI-1 exists in both an active and an inactive, latent form.3 The antigen test is unable to distinguish between active and inactive PAI-1. Given these findings, it is best to analyze both PAI-1 antigen and activity levels simultaneously. If the patient has delayed surgical or posttraumatic bleeding with all other known deficiency states having been evaluated and ruled-out, and the PAI-1 activity level is <1 IU mL-1, PAI-1 deficiency can be considered. Concurrently run t-PA levels might also be performed and may be elevated.

Since tumor necrosis factor alpha, IL-1, -2 and -6, and transforming growth factor beta can induce increased activity of PAI 1, infection and inflammation can mask low levels of PAI-1 when an individual has some ability to produce the protein.76-80

PAI-1 activity increases immediately in association with surgery and is responsible for the down regulation and control of fibrinolysis.81 Elevated levels are seen with metabolic syndrome82 and obesity possibly because PAI-1 is secreted by adipocytes.83 A reduction in levels of PAI-1 is seen with estrogen treatment.84 Finally the 4G/5G polymorphism in the promoter region of the PAI-1 gene also has an effect on measured activity levels as mentioned above.85