Saleh Shamse Basha: When ‘Low Protein S’ Isn’t Necessarily Low
Saleh Shamse Basha, Senior Hematology Technologist (Reference Lab, HQ) at PureLab, shared a post on LinkedIn:
“When ‘Low Protein S’ Isn’t Necessarily Low.
A quick coagulation puzzle
A patient’s Protein S activity low and also ProC Global (APCR) test comes back low too.
Two abnormal results pointing the same direction it must be a real thrombophilia, right?
Not accrually.
- Pre-Analytical Trap (Platelet-Poor-plasma).
Both of these are clotting tests because Protein S is the cofactor APC needs to work so when one drops the other often follow.
If the frozen plasma has a leftover platelets that means the sample wasn’t spun down properly before freezing, those platelets rupture on thaw and release phospholipid (plus stored Factor V) into the plasma.
That extra material speeds up clotting artificially and both tests read ‘faster clotting’ as ‘weaker anticoagulant activity.’
The result: a falsely low Protein S and a falsely abnormal APCR that reflect nothing about the patient’s actual biology.”

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