# A case of protein S-specific activity triggers detection with potential thrombosis development

## TL;DR

A patient with decreased protein S-specific activity and a genetic variant had an increased risk of thrombosis, highlighting the importance of measuring this specific activity.

## Contribution

Demonstrates the clinical relevance of measuring protein S-specific activity in identifying thrombosis risk beyond standard protein S activity and antigen levels.

## Key findings

- The patient had normal protein S activity and antigen levels but decreased protein S-specific activity.
- A genetic variant (protein S Tokushima) was identified as a potential cause of thrombophilia.
- Measuring protein S-specific activity can reveal increased thrombosis risks not detected by standard tests.

## Abstract

Protein S gene abnormalities are the most common congenital predisposition to thrombophilia in the Japanese population, but not in the Caucasian population. It is important to measure protein S activity, specific activity, and antigen levels in patients with thrombophilia. A 52-year-old man presented with suspected deep vein thrombosis after previously visiting an orthopedic clinic with right lower extremity swelling after his long-distance walk 5 days prior. His D-dimer level was elevated, and a thrombus was found from the femoral to the below-the-knee veins on ultrasonographic echography. Anticoagulation therapy was initiated. His parents had previously been diagnosed with deep vein thrombosis; therefore, he was examined for thrombophilic predisposition. The results showed normal protein S activity and antigen levels, but decreased protein S-specific activity. Genetic testing revealed the presence of a protein S variant (protein S Tokushima). In addition to measuring protein activity and antigen levels, protein S-specific activity measurements can reveal increased risks of thrombosis.