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Test ID: APCR
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Activated Protein C Resistance
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Useful For
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Useful in the evaluation of thrombophilia .
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Method name and description
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Turbidimetric
Test is performed using Sysmex CS5100 analyzer. When activated Protein C (APC) is added to plasma and an APTT is performed, there is normally a prolongation of the clotting time as a result of factor V and factor VIII degradation. The sample is prediluted with factor V deficient plasma to overcome possible deficiency of other coagulation factors. Presence of factor V Leiden will lead to shortening of the clotting time.
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Clinical information
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Protein C is a part of the natural anticoagulant system and it is a vitamin K-dependent protein zymogen that is synthesized in the liver and circulates at a plasma concentration of approximately 5 mcg/mL. Protein C is activated to activated protein C (APC) via proteolytic cleavage by thrombin bound to thrombomodulin, an endothelial cell surface membrane protein. APC downregulates the procoagulant system by proteolytically inactivating procoagulant factors Va and VIIIa. Protein S, another vitamin K-dependent coagulation protein, catalyzes APC inactivation of factors Va and VIIIa. APC interacts with and proteolysis factors V/Va and VIII/VIIIa at specific APC binding and cleavage sites, respectively. Resistance to activated protein C (APC resistance) is a term used to describe abnormal resistance of human plasma to the anticoagulant effects of human APC. APC resistance is characterized by a reduced anticoagulant response of patient plasma after adding a standard amount of APC. This generally indicate the presence of FV Leiden which is an abnormal version of factor V that is resistant to the proteolytic action action of APC.
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Specimen type / Specimen volume / Specimen container
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Plasma Na Cit. Plasma poor platelets
Specimen Volume: 2.7ml.
Container/Tube: Light Blue top (3.2% Sodium Citrate)
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Collection instructions / Special Precautions / Timing of collection
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- Samples collected in HMC facilities MUST reach the coagulation laboratory within 1 hour of collection.
- Samples collected in non-HMC facilities / external clients: MUST reach coagulation laboratory within 1 hour of collection, if not applicable, centrifuge the whole blood and carefully remove the plasma (by pipette not by decanting) and send it in a temperature-controlled environment (18- 25 ºC) within 2 hours of centrifugation. If the transportation of the plasma can’t be within a maximum of 2 hours, prepare platelet-poor plasma as follows:
- Re-centrifuge the plasma again.
- Remove the top portion of plasma leaving approximately 250 ul in the bottom to discard.
- The double-centrifuged plasma should be aliquoted into labeled plastic tubes.
- Freeze immediately at -20 ºC or below
- Specimens must arrive frozen.
- If patient HCT is >55%, test will not be processed. The ordering Physician will be contacted to reorder the test and call the patient to go to Phlebotomy for recollection. Instruct the patient to inform the phlebotomy about his high HCT% , the phlebotomy will contact the lab to request a coagulation tube after adjusting amount of anticoagulant.
Note:
Collection of blood for coagulation testing through intravenous lines that have been previously flushed with heparin should be avoided, if possible. If the blood must be drawn through an indwelling catheter, possible heparin contamination and specimen dilution must be considered. When obtaining specimens from indwelling lines that may contain heparin, the line should be flushed with 5 mL of saline, and the first 5 mL of blood or 6-times the line volume (dead space volume of the catheter) be drawn off and not used for coagulation testing. For those specimens collected from a normal saline lock (capped off venous port) twice the dead space volume of the catheter and extension set should be discarded.
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Relevant clinical information to be provided
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Patient/family history of thrombotic disorder.
History of chronic diseases .
Patients suspected with the FV Leiden mutation will show APC resistance by this test.
Further testing by molecular genetics will detect the mutation if present.
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Storage and transport instructions
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Specimen Rejection Criteria
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Specimens with no label or missing required identification
Broken, leaking or contaminated specimen
Clotted samples
Under-filled or overfilled sample tubes.
Wrong sample container sample received
Improper specimen transport temperature (e.g. like specimens which are needed to be sent on ice)
Old specimen (test-dependent)
Grossly Hemolyzed sample (test-dependent)
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Biological reference intervals and clinical decision values
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Normalized Ratio: 0.91– 1.19 %. .
With the currently used reagent, a cut-off of 0.7 for normalized ratio has a sensitivity of 98% for FV Leiden and a specificity of 99%.
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Factors affecting test performance and result interpretation
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No interference up to:
Triglycerides 1077 mg/dL
Hemoglobin 1000 mg/dL
Bilirubin 60 mg/dL
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Turnaround time / Days and times test performed / Specimen retention time
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