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Easy, specific, and stable protein S antigen testing

The INNOVANCE® Free PS Ag assay is straightforward to use and easily fits into the laboratory routine. Meanwhile, the ISTH Guideline1 recognizes that free protein S antigen assays are the first-line diagnostic for protein S deficiency. The INNOVANCE Free PS Ag assay is a liquid latex reagent with high specificity for free protein S using two different antibodies that do not bind to protein S/C4b-binding protein complexes. In addition, this assay shows low interference with rheumatoid factors and heterophilic antibodies.

Features & Benefits

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Economical testing

  • The liquid, truly ready-to-use reagent requires no additional mixing or standing time, so it is easy to handle without the wait on Siemens Healthineers hemostasis systems.

  • The assay is economical to use, with superior once-opened stability of 8 weeks at 2–8°C.

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Excellent precision

  • The assay provides high linearity and excellent precision over the entire measuring range of 10–150% of norm.
  • The INNOVANCE Free PS Ag assay shows no major interferences, including interferences from rheumatoid factors and heterophilic antibodies.

Technical Specifications

No waiting time

Liquid, ready-to-use reagent requires no manual preparation or standing time

152 tests
Number of tests per kit

96 hours
Onboard stability

10-150% of norm
Measuring range

Within-device CV of Control Plasma N

8 weeks
Stability once opened at 2–8°C

The INNOVANCE Free PS Ag assay is a turbidimetric, latex-based assay that employs a liquid, ready-to-use reagent. The assay consists of three components and can be ordered as a kit.



INNOVANCE Free PS Ag Assay kit

  1. Siemens Healthineers INNOVANCE VWF Ac reagent I

    INNOVANCE Free PS Ag Buffer

    Ready-to-use liquid containing a heterophilic blocking reagent and preservatives.

Sysmex CN-3000/6000 Systems
Available on CN-3000/6000 Systems.3

For details on available assay applications and ordering information, download the hemostasis reagent portfolio catalogue.

Clinical Use

Complete thrombophilia and protein S testing portfolio 

The Siemens Healthineers INNOVANCE Free PS Ag and Protein S Ac assays support differentiation between type I and type II protein S deficiencies. Combined with other Siemens Healthineers thrombophilia assays, the INNOVANCE Free PS Ag assay completes your lab's thrombophilia testing portfolio. Now you can obtain a broad thrombophilia testing solution from a single, trusted supplier, streamlining your ordering and administration processes. Benefit from excellent result correlation across Siemens Healthineers hemostasis testing platforms.

About protein S

Protein S is a plasma protein produced in the liver. It is an anticoagulant, functioning as a cofactor for protein C-mediated inhibition of activated factor V and factor VIII. There are two forms of protein S in plasma: free protein S (the active form) and protein S bound to C4b-BP. Synthesis of protein S is vitamin K-dependent, and normal activity for protein S ranges from 60-130% of norm.

Protein S deficiency and venous thrombosis

Protein S deficiency is a risk factor for venous thrombosis. Therefore, protein S testing plays an important role in thrombophilia screening. Protein S deficiency may be congenital or acquired in many ways, including oral anticoagulation therapy, hepatic or kidney disorders, pregnancy, and oral contraceptives or estrogen therapy.

Protein S determination

Several methods currently exist for determination of protein S. Functional assays such as protein S Ac assays measure protein S activity. In contrast, immunoassays measure different types of protein S antigen. Free protein assays measure free protein S only, while total protein S assays measure both free and bound protein S antigen. According to latest guidelines, the initial assay for congenital PS deficiency should be the free PS antigen assay.

  • Before testing for protein S deficiency, causes of acquired deficiencies and for interfering factors should be assessed. Testing for congenital protein S deficiency on patients with acquired conditions is recommended to be deferred.
  • Protein S deficiency was classified into three phenotypes (type I, II, and III) by Bertina in 1991 (during the ISTH-SSC meeting).
  • A free protein S Ag assay is recommended as the initial assay for congenital Protein S deficiency. A total Protein S Ag assay can be performed to differentiate between type I and type III deficiency but is recognized to provide little clinical information. Protein S activity testing in a patient with a normal free protein S Ag result may be useful in case of strong clinical suspicion, to identify Protein S type II deficiency. Protein S activity is measured with a protein S Ac assay, an activated protein C (APC)-cofactor activity test using the factor Xa-pathway. It uses Russell’s viper venom (RVV) as a factor X-activator by adding protein S-deficient plasma and APC.
  • If an abnormal value is obtained, testing must be repeated after at least 4 weeks for confirmation.
  • There are different types of protein S activity and antigen assays1,2 that generate different result levels. Samples from a given patient should always be measured with the same type of assay.
  • The current protein S type II deficiency is an APC-cofactor deficiency. A deficiency in TFPIα-cofactor activity (single or pleiotropic with APC-cofactor) was recently described. To date, no cases of these subtypes have been reported. Moreover, its association with venous thromboembolism is not yet established. 
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