Ordering Recommendation

Use to detect and subtype protein S deficiency. Do not order if individual has been on warfarin therapy in the previous 2-4 weeks.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Lt. blue (sodium citrate). Refer to Specimen Handling at aruplab.com for hemostasis/thrombosis specimen handling guidelines.

Specimen Preparation

Transfer 2 mL platelet-poor plasma to an ARUP Standard Transport Tube. (Min: 1 mL)

Storage/Transport Temperature

CRITICAL FROZEN. Separate specimens must be submitted when multiple tests are ordered.

Unacceptable Conditions

Serum. EDTA plasma, clotted or hemolyzed specimens.


Ambient: 4 hours; Refrigerated: Unacceptable; Frozen at -20°C: 3 months, at -70°C: 6 months


Microlatex Particle-Mediated Immunoassay




1-4 days

Reference Interval

1-89 days: 15-55%
90-179 days: 35-92%
180-364 days: 45-115%
1-5 years: 62-120%
6-9 years: 62-130%
10-17 years: 60-140%
18 years and older Male: 74-147%
18 years and older Female: 55-123%

Interpretive Data

Patients on warfarin may have decreased free protein S values. Patients should be off warfarin therapy for two weeks for accurate measurement of free protein S levels. Decreased levels of free protein S are also associated with DIC, liver disease, pregnancy, and inflammatory syndromes.

Compliance Category



If low Protein S Free Antigen is detected, then Protein S, Total Antigen, will be added. Additional charges apply.

Hotline History


CPT Codes

85306; if reflexed, add 85305


Component Test Code* Component Chart Name LOINC
0098894 Protein S Ag Free 27821-8
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • Protein S Profile
  • Protein S, Free and Total Antigen
Protein S, Free Antigen with Reflex to Protein S, Total Antigen