OUP user menu

Protein S Assays
An Analysis of North American Specialized Coagulation Laboratory Association Proficiency Testing

Elizabeth M. Van Cott MD, Marlies Ledford-Kraemer MBA, MT, Piet Meijer PhD, William L. Nichols MD, Stephen M. Johnson MT, Ellinor I.B. Peerschke PhD
DOI: http://dx.doi.org/10.1309/BG1GR3ANAR9905F4 778-785 First published online: 1 May 2005


To assess current laboratory practice and the performance of different reagent-instrument combinations for protein S testing, protein S results from the North American Specialized Coagulation Laboratory Association (NASCOLA) proficiency testing surveys for 2002 and the first half of 2003 were analyzed. A written survey of NASCOLA laboratories also was performed to further assess current laboratory practices for protein S testing. The free protein S antigen assays and the Diagnostica Stago Staclot protein S assay were extremely accurate in detecting a heterozygous type I protein S deficiency. Another functional protein S assay and most total protein S assays were less reliable, depending to some extent on the instrument. All assays used by NASCOLA laboratories appropriately identified normal protein S specimens. NASCOLA laboratories performed at least as well as European Concerted Action on Thrombosis laboratories in the proficiency tests. The results suggest that the diagnosis of heterozygous protein S deficiency may be problematic with some currently available assays. Many total protein S antigen assays do not add to the diagnosis and can be unreliable for protein S deficiency subtyping. Better standardization of functional and antigenic assays is needed.

Key Words:
  • Protein S
  • Proficiency testing