George had a phone conversation with a reference lab colleague who generated protein S levels on a patient specimen: free and total protein S concentrations over 70%, clot-based protein S activity less than 1%. PT normal, PTT prolonged by about 15 seconds. DRVVT prolonged, not shortened by platelet phospholipid-rich reagent. What could account for these findings, and what would you do next?
Added on 3-29-18: My colleague ran a thrombin time; the result was normal, and also found that two addition specimens from the same facility had similar results. Does this change your assessment? Geo.