Protein Spot 3: Protein S (Protein S Antigen) in Plasma
This test measures the amount of Protein S, a vitamin K-dependent protein that helps prevent blood clots by regulating other clotting factors. Protein S is important for maintaining healthy blood flow.
["Protein S supports blood clot prevention and helps maintain healthy circulation."]
Key facts at a glance
- LOINC
- 35321-9
- Short code
- Prot sp3 p sincalide Fld-mCnc
- Synonyms
- Prot sp3 p sincalide Fld-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why Is This Test Done?
Your healthcare provider may order this test to check for conditions that affect blood clotting, such as inherited or acquired deficiencies in Protein S. It may also be used to monitor treatment for conditions like thrombophilia or to evaluate symptoms like easy bruising, excessive bleeding, or unexplained clots.
What to Expect Before the Test
No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if your blood is drawn in the morning. Avoid smoking or consuming alcohol for a few hours beforehand. Bring any medications or supplements you’re taking to your appointment.
What Happens During the Test?
A healthcare professional will insert a small needle into a vein in your arm to draw a blood sample. You may feel a brief pinch, but it usually doesn’t cause discomfort. The blood will be sent to a lab for analysis.
What to Expect After the Test
After the blood is drawn, the needle site will be bandaged. You may experience mild bruising or soreness, but this usually goes away quickly. Avoid heavy lifting or strenuous activity for a few hours to prevent excessive bleeding.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Low levels of Protein S can increase your risk of blood clots (thrombosis) or bleeding disorders. It may be linked to conditions like antiphospholipid syndrome, liver disease, or certain medications. High levels may rarely be associated with other health concerns, but this is less common. Your provider will interpret results in the context of your medical history and symptoms.
Short name
Protein S Level (Plasma)
Frequently asked questions
How long does it take to get results?
What does a low Protein S level mean?
Can I eat or drink before this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy