Test Details
Methodology
The patient plasma is added to PS-depleted normal plasma with normal levels of all factors but PS. The mixture is supplemented with excess aPC and factor V is then added. The extent of prolongation of the time to clot formation after calcium chloride is added is proportional to plasma PS activity.
Result Turnaround Time
2 - 3 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Use
This test is used for confirmation and characterization of protein S (PS) congenital deficiency.
Special Instructions
If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer to Coagulation Collection Procedures for directions.
Limitations
The presence of heparin or lupus anticoagulants leads to overestimation of PS. aPC resistance due to factor V Leiden mutation or some other cause can falsely lower measured PS activity levels.6
Custom Additional Information
See Protein S Deficiency Profile [117754] for more clinical information.
Specimen Requirements
Specimen
Plasma, frozen
Volume
1 mL
Container
Blue-top (sodium citrate) tube
Collection Instructions
Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples, except when using a winged blood collection device (i.e., "butterfly"), in which case a discard tube should be used.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a Labcorp PP transpak frozen purple tube with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Stability Requirements
| Temperature | Period |
|---|---|
| Frozen | 28 days |
| Freeze/thaw cycles | Stable x3 |
Reference Range
| Age | Range |
| 1 d | 28–47% |
| 3 d | 33–67% |
| 1 to 11 m | 29–162% |
| 1 to 5 y | 67–136% |
| 6 to 10 y | 64–154% |
| 11 to 16 y | 65–140% |
| >16 y | 54–129% |
Storage Instructions
Freeze.
Patient Preparation
Avoid warfarin (Coumadin®) therapy for two weeks and heparin therapy for two days prior to the test. Do not draw from an arm with a heparin lock or heparinized catheter.
Causes for Rejection
Gross hemolysis; clotted specimen; frozen specimen thawed in transit; improper labeling
References
Gupta A, Tun AM, Gupta K, Tuma F. Protein S Deficiency. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan. 2022 Dec 5. PubMed 31335064
Moore GW. Thrombophilia Screening: Not So Straightforward. Semin Thromb Hemost. 2024 Nov;50(8):1131-1152. PubMed 38733983
STA® – Staclot® Protein S Instructions For Use (IFU) [package insert]. May 2018.
Footnotes
7. Summerhayes R, et al. J Thromb Haemost. 2007;5(Supp 2):P-S-397.
8. Labcorp internal validation of adult reference interval for protein S functional.
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 164525 | Protein S-Functional | 27822-6 | 164526 | Protein S-Functional | % | 27822-6 |
| Order Code | 164525 | |||||
| Order Code Name | Protein S-Functional | |||||
| Order Loinc | 27822-6 | |||||
| Result Code | 164526 | |||||
| Result Code Name | Protein S-Functional | |||||
| UofM | % | |||||
| Result LOINC | 27822-6 |