Total Protein S
Total Protein S — Trimester-Specific Reference Ranges
Total Protein S includes both bound and free fractions. Although total Protein S decreases in pregnancy, the fall in free Protein S is much more pronounced and clinically relevant.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| % (total antigen) | 70 – 140 | 39 – 105 | 27 – 101 | 33 – 101 |
Physiologic changes in pregnancy
- Total Protein S decreases slightly in pregnancy.
- Free Protein S decreases markedly due to ↑ C4b-binding protein binding capacity.
- Pregnancy-associated hypercoagulability reduces Protein S activity.
- Testing for hereditary Protein S deficiency should ideally occur postpartum.
Causes of low total Protein S
- Expected physiologic reduction in pregnancy
- Hereditary Protein S deficiency (Types I–III)
- Liver disease (reduced synthesis)
- Vitamin K deficiency
- Consumptive coagulopathy (e.g., DIC)
- Acute thrombosis (consumption)
- Nephrotic syndrome (urinary protein loss)
- Inflammatory states (↑ C4b-binding protein)
- Estrogen therapy
- HIV or varicella infection
Causes of high total Protein S
- Rare compensatory elevations after thrombosis
- Occasional idiopathic increases
- Generally not associated with clinical pathology
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table. Obstet Gynecol. 2009;114:1326–31. PMID: 19935037
- Khor B, Van Cott EM. Laboratory evaluation of hypercoagulability. Clin Lab Med. 2009;29:339–66.
- Laboratory Test Handbook. Jacobs DS et al., 5th ed., Lexi-Comp.