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Protein S qualitative screening test (using a probe-based assay)

Published: August 9, 2026Updated: August 16, 2026

This test checks for the presence of Protein S, a natural blood protein that helps prevent abnormal blood clots. It is often used to evaluate inherited or acquired conditions that may increase your risk of clotting.

Quick summary

["Protein S helps maintain healthy blood flow by supporting blood thinning processes; low levels may raise clot risk."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
93393-7
Short code
Proteus sp DNA Bld Pos Ql NAA+probe
Synonyms
Proteus sp DNA Bld Pos Ql NAA+probe
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
probe-amp-tar
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Might Be Ordered

Your healthcare provider may recommend this test if you have a history of blood clots, certain blood disorders, or symptoms like leg swelling, unexplained bruising, or fatigue. It may also be part of screening for conditions like antiphospholipid syndrome or inherited thrombophilia.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm or vein to draw blood. If you’re taking blood thinners, let your provider know before the test.

What the Results Mean

This test provides a qualitative result (positive or negative) rather than a specific quantity. A positive result suggests sufficient Protein S levels, while a negative result may indicate low levels that could increase clotting risk.

Common Conditions Linked to Protein S Deficiency

Low Protein S levels are associated with conditions like venous thromboembolism (blood clots in veins), arterial clots, or recurrent pregnancy losses. It’s not a standalone diagnosis but may guide further testing or treatment.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Protein S Screening (Qualitative)

Frequently asked questions

What does a positive result mean?
A positive result means Protein S is present in your blood, supporting normal clotting regulation. However, this test alone cannot confirm a diagnosis of Protein S deficiency; further testing may be needed if symptoms or risk factors are present.
How often should I get this test?
Your provider will determine frequency based on your medical history, symptoms, and risk factors. Some patients may need periodic monitoring if they have a history of clotting disorders.
Can I eat or drink before this test?
You can eat and drink normally before the test unless instructed otherwise. Avoid alcohol or caffeine in excess, as they may affect blood clotting temporarily.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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