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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Protein S Activity

Test Code(s): PS-ACT / XPSF

CPT Code(s): 85306

Methodology: Mechanical Clot Detection

Clinical Significance: Test is used for the qualitative determination of plasma Protein S activity by clotting method.

Days Performed: Mon-Fri, dayshift - day varies. Specimens are accepted at any time. Testing required during off hours must be approved by a Coagulation physician. Call 263-5005 before collection.

Turnaround Time: Stat: 1 working day.
Routine: 7 - 10 working days.

Specimen Requirements

Specimen: Blood

Patient Preparation: Patient must be off warfarin therapy for at least one week. See additional information below.

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.  

Please indicate patient history and if patient is receiving anticoagulant (warfarin/ Heparin/Vitamin K antagonist), direct thrombin inhibitor or fibrinolytic agent therapy and duration.

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: 1.5 mL
Pediatrics: 0.5 mL

Specimen Processing: Centrifuge specimen to yield platelet poor plasma (platelet count should be less than 10 K/uL). Separate plasma and transfer to plastic tube or vial. 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).

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. Test cannot be done if patient is receiving coumadin.

Stability: Ambient: 4 hours on spun tube
Refrigerated: Not acceptable
Frozen: 2 weeks at -20C; 6 months at -70C


Reference Interval:


Male:                      %NPP

0-4 days                 51-96   

5 days and up         75-140 


Females:                 %NPP

0-4 days                 51-96

5 days and up         55-130

Test Limitations:

Patients on oral anticoagulants will have decreased functional protein S values.

Patients should be off of oral anticoagulant therapy for one week for accurate functional protein S levels.


Artifactually decreased functional protein S values may be seen in patients with abnormally elevated levels of FVIII(>250%NPP).


Artifactually elevated levels of functional protein S may be seen in samples with heparin >1U/mL or the presence of thrombin inhibitors.

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