Factor XII (plasma)
Factor XII (Hageman factor) is part of the contact activation pathway. In contrast to Factors XI and V, Factor XII rises progressively during pregnancy due to estrogen-mediated hepatic synthesis.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| % | 50 – 150 | 78 – 124 | 90 – 151 | 129 – 194 |
Pregnancy physiology
- Factor XII increases progressively through gestation.
- Despite prolonging the aPTT, Factor XII is not required for physiologic hemostasis.
- Elevations reflect estrogen-driven hepatic synthesis.
Causes of low Factor XII
- Inherited Factor XII deficiency
- Liver disease
- Severe systemic inflammation
Isolated Factor XII deficiency causes a prolonged aPTT but does not cause clinical bleeding, even at very low levels.
Causes of elevated Factor XII
- Normal pregnancy physiology
- Estrogen exposure
- Acute inflammatory states
Clinical interpretation & pregnancy considerations
- Low Factor XII does not contraindicate neuraxial anesthesia.
- A prolonged aPTT with normal FVIII, FIX, and FXI often indicates FXII deficiency.
- Very high levels may be associated with thrombosis risk, but pregnancy-specific thresholds are undefined.
- Postpartum re-testing helps distinguish transient pregnancy-related changes.
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.
- Girolami A, et al. Clinical relevance of factor XII deficiency. J Thromb Haemost. 2004.
- Brenner B. Haemostatic changes in pregnancy. Thromb Res. 2004.
- James AH. Pregnancy-associated changes in coagulation. Hematol Oncol Clin North Am. 2011.