Tissue plasminogen activator (tPA) antigen — plasma
Tissue plasminogen activator is a key enzyme in fibrinolysis that converts plasminogen to plasmin. During pregnancy, tPA antigen levels rise progressively, but net fibrinolytic activity is reduced due to marked increases in plasminogen activator inhibitors (PAI-1 and PAI-2).
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| ng/mL | 1.6 – 13 | 1.8 – 6.0 | 2.4 – 6.6 | 3.3 – 9.2 |
Pregnancy physiology
- tPA antigen levels rise gradually across gestation.
- Pregnancy is a prothrombotic state with reduced effective fibrinolysis.
- Placental production of PAI-2 markedly increases in the 2nd and 3rd trimesters.
- Most circulating tPA becomes PAI-1/PAI-2 bound and functionally inhibited.
- tPA antigen assays reflect both active and inhibited tPA.
Causes of elevated tPA
- Preeclampsia and severe gestational hypertension
- Placental dysfunction and fetal growth restriction
- Acute thrombosis or endothelial injury
- Sepsis and systemic inflammatory states
- Advanced maternal age
- Thrombolytic therapy
Causes of low tPA
- Marked elevation of PAI-1 or PAI-2 (typical of late pregnancy)
- Genetic deficiency of tPA (rare)
- Severe hepatic dysfunction
- Suppressed endothelial activity
Clinical interpretation & pregnancy considerations
- Despite rising tPA antigen, net fibrinolysis is reduced in pregnancy.
- This contributes to protection from hemorrhage but increases thrombotic risk.
- Marked abnormalities may be seen in preeclampsia, abruption, and placental disease.
- Interpret alongside PAI-1, PAI-2, D-dimer, fibrinogen, and clinical context.
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.