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Test Code LAB492 Protein S Antigen (Free)

Important Note

Blue tubes that are not filled to the required line will not be processed, due to result integrity being affected.  

Useful For

Useful for detecting deficiencies significant in the diagnosis of thrombosis.   Protein S acts as a necessary cofactor to activated protein C, playing a part in the plasma anticoagulant system.

Decreased levels of protein S antigen can be seen in:

  • Congenital defects (Type I, III)
  • Vitamin K deficiency
  • Inflammatory syndrome
  • Hepatic disorders
  • Nephrotic syndrome
  • Oral contraceptives, anticoagulants, L-asparaginase

Elevated protein S levels are of uncertain clinical significance.

Methodology

Immunoturbidimetric

Performing Laboratory

Bozeman Health Laboratory Services

Specimen Requirements

Specimen must arrive and be tested within 4 hours of draw.
 

Specimen Type: Whole blood
Container/Tube: Blue top (3.2% sodium citrate)

Specimen Volume: Full tube

Collection Instructions: Click here to link to a You Tube video tutorial

1. Immediately after draw, invert tubes several times to mix blood with additive.

2. Send specimen in original tube.

3. If there is a delay in transport of >4 hours, specimen must be double-centrifuged to prepare a platelet-free plasma specimen as follows:

a. Immediately centrifuge at 3,200 rpm for 15 minutes.

b. Carefully remove plasma from cells avoiding platelet/buffy coat, and transfer plasma into a plastic tube.

c. Centrifuge plastic tube at 3,200 rpm for 15 minutes.

d. Carefully remove top portion of plasma and transfer plasma into a plastic tube leaving approximately 250 mL in bottom to discard.

e. Double-centrifuged plasma should be aliquoted (0.5 mL-1 mL each) into clearly labeled plastic tubes. (Glass vial is not acceptable.)

Note: Number of tests ordered will determine number of aliquots needed, generally 1 aliquot per test.

f. Specimens should be frozen at <-40° C, if possible, and sent together in same container with at least 5 lbs of dry ice. Specimens must arrive in a frozen state.

Additional Information: Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.

Specimen Transport Temperature

Ambient (whole blood) <4 hours/Frozen (plasma) >4 hours

Specimen Stability

Specmen Type Temperature Time
Whole Blood (unspun) Ambient 4 hours
Plasma Na Citrate (spun) Ambient 4 hours
Plasma Na Citrate (double spun) Frozen 14 days

Reference Values

Males: 70-148%

Females: 50-134%

Additional Information

  • During pregnancy,there is a decrease in free protein S level.
  • Direct acting oral anticoagulants (eg, direct thrombin inhibitors: DTI, such as dabigatran [Pradaxa], argatroban [Acova], bivalirudin [Angiomax]) and direct factor Xa inhibitors (eg, rivaroxaban [Xarelto], apixaban [Eliquis], edoxaban [Savaysa]) may cause the protein S activity to appear spuriously normal (or elevated), when protein S activity is truly decreased (or normal). Clinical correlation is suggested, and in the absence of anticoagulation therapy, consider repeating the protein S activity and antigen assay.  
  • Coumadin therapy may result in decreased protein S activity and free protein S antigen.

Day(s) Test Set Up

Thursday

Test Classification and CPT Coding

85306-Protein S Ag, Free