Additional Test Information
Citrated Plasma (light blue top)
Additional Sample Requirements
Protein S activity is measured by a prothrombin-time-based clotting method. Patients should be off warfarin for at least 4 weeks before drawing a sample. The assay kit manufacturer has demonstrated the assay to be unaffected by levels of unfractionated heparin or low molecular weight heparin up to 2 IU/mL, but the results may be artifactually elevated in samples containing dabigatran or rivaroxaban. Platelet contamination of plasma samples causes an under-recovery of Protein S level, and proper sample preparation is required. Age and gender specific reference intervals are used.
Additional Sample Information