Skip to Content
UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Protein S Antigen, Free

Test Code(s): PSFREE / HCPSFREE

CPT Code(s): 85306

Methodology: Immunoturbidimetry

Request Form: UWHC Special Coagulation Outreach Request Form (UWH SCLR-O)

Days Performed: Mon-Fri, dayshift - day varies.

Turnaround Time: Stat: Not available stat.
Routine: 7 - 10 working days.


Specimen Requirements

Specimen: Blood

Patient Preparation: Patient must be off warfarin therapy for at least one week or on a stable dose of warfarin for at least one week.

Collection Instructions: Do NOT draw through a line containing heparin. The venipuncture MUST be atraumatic to avoid hemolysis and contamination with tissue factors and platelets. Tube must be allowed to fill completely.  

Indicate if patient is receiving anticoagulant (warfarin/ Heparin/Vitamin K antagonist), direct thrombin inhibitor or fibrinolytic agent therapy.

Collection Container: Preferred: Light blue top (3.2% NaCitrate)

Collection Volume: Preferred: Full 3.5 mL tube
Pediatrics: Pediatric tube filled to fill mark

Sample Analyzed: Plasma

Volume Required: Preferred: 1 mL
Pediatrics: 0.5 mL

Specimen Processing: Ultracentrifuge sample and label "ULT".  If an ultracentrifuge is not available, centrifuge specimen to yield platelet poor plasma (platelet count should be 10K/uL or less). Separate plasma and transfer to plastic tube and spin again. Transfer plasma from second spin to clean plastic tube or vial. Indicate on the tube "spun twice". Freeze plasma within 4 hours of collection at
-20C or below.

Specimen Transport: Transport whole blood specimen at room temperature to UWHC Core Laboratory (B4/220) within 4 hours of collection. See Specimen Processing for instructions if transport criteria are not met. Transport frozen plasma aliquot on dry ice to UWHC Core Laboratory (B4/220).

Outreach Specimen Transport: Centrifuge specimen to yield platelet poor plasma (platelet count should be 10 K/µL or less). Separate plasma and transfer to labeled plastic tube and spin again. Transfer plasma from second spin to clean plastic labeled tube or vial. Indicate on tube "spun twice". Freeze plasma within 4 hours of collection at -20°C or below.

Unacceptable Criteria: Hemolyzed specimens, clotted specimens, partially filled tubes and whole blood specimens greater than 4 hours old when received by the laboratory are not acceptable. Specimens from patients who have not been off warfarin therapy for at least one week or on a stable dose of warfarin for at least one week are not acceptable.

Stability: Ambient: 4 hours on a spun tube
Refrigerated: Not acceptable
Frozen: 1 month at -20C; 6 months at -70C


Interpretation

Reference Interval:
 MALES  
 0-6 days:  30-85%
 7 days-3 months:  40-110 %
 4-11 months:  50-115 %
 12 months and up:  70-150 %
   
 FEMALES  
 0-6 days:  30-85 %
 7 days-3 months:  40-110 %
 4-11 months:  50-115 %
 12 months and up:  60-150 %

Test Limitations:

The presence of rheumatoid factor leads to an over-estimation of the free protein S level.  The presence of anti-bovine albumin and/or anti-mouse antibodies in certain subjects may lead to an over-estimation of the free protein S level.

Additional Information:

A clotting test for Protein S (functional portion) is also available (see Protein S Activity).

Protein S - Free, Free Protein S

Back to Lab Test Directory Index