Interference of factor V Leiden on protein S activity: Evaluation of a new prothrombin time-based assay

Armando Tripodi, Daniela Asti, Veena Chantarangkul, Eugenia Biguzzi, Pier Mannuccio Mannucci

Research output: Contribution to journalArticlepeer-review


Protein S activity in plasma from factor V Leiden (FVL)-positive patients may be lower than expected. We investigated a new commercially available method for protein S for such interference. Protein S activity was measured for plasmas from 50 individuals with FVL and their results were compared with those obtained for plasmas from 47 sex-matched and age-matched individuals without FVL. We assumed that the median protein S activity value from a relatively large number of individuals with or without FVL would not be significantly different if there is no influence from FVL. The FVL-positive plasmas gave relatively (albeit not significantly) lower protein S levels than FVL-negative plasmas when both were tested undiluted (86 versus 93 IU/dl, P = 0.06). Those differences were reduced (98 versus 102 IU/dl, P = 0.58) when testing was performed on diluted plasmas. Furthermore, the proportion of patients with FVL identified as low-abnormal on the basis of the specific cut-off values (undiluted = 64 U/dl; diluted = 71 IU/dl), which was 8% when testing was performed on undiluted plasmas, was reduced to 4% when testing was performed on diluted plasmas. Conversely, the corresponding proportions of patients without FVL remained unaltered (4.3 versus 4%). In conclusion, these results indicate that the evaluated method is somewhat affected by FVL and that dilution of plasma prior to testing improves specificity. Protein S activity measurement for FVL-positive patients should be performed on diluted plasma and the results interpreted on the basis of the cut-off value specifically determined for diluted plasmas.

Original languageEnglish
Pages (from-to)543-546
Number of pages4
JournalBlood Coagulation and Fibrinolysis
Issue number6
Publication statusPublished - Sep 2007


  • Congenital deficiency
  • Screening
  • Thrombophilia
  • Thrombosis

ASJC Scopus subject areas

  • Hematology


Dive into the research topics of 'Interference of factor V Leiden on protein S activity: Evaluation of a new prothrombin time-based assay'. Together they form a unique fingerprint.

Cite this