Platform
Company
Immunology & Autoimmune
Review status
Currently under review
Pending specialist review and validation.
The Activated Protein C (APC) Resistance Preliminary test is a screening blood test that looks at how your blood responds to activated protein C, a natural anticoagulant that helps prevent excessive clotting. The assay measures clotting time in your plasma after adding specific reagents to see whether APC can slow the clotting process as expected.
This test is often used as an initial screen for decreased responsiveness to APC, which can be inherited or acquired. If the screen suggests resistance, your clinician may order a confirmatory functional assay or a genetic test for Factor V Leiden to clarify the cause.
APC resistance is a common cause of an inherited tendency to form blood clots in the veins. Finding it can help explain past events such as deep vein thrombosis or pulmonary embolism and can guide decisions about further evaluation. It may also be considered when there is a strong family history of clots or in selected cases of pregnancy complications.
Clinicians may order this test when a clot occurs at a young age, in unusual locations, or without clear triggers, or before starting estrogen therapy in someone with concerning history. Results are interpreted together with your history, examination, and other laboratory tests to decide on next steps.
If your result suggests normal sensitivity to activated protein C, the likelihood of APC resistance is lower, and additional testing may not be needed unless your history points strongly to a clotting tendency. If your result suggests resistance, your clinician may recommend confirmatory testing, such as a more specific functional assay or genetic testing for Factor V Leiden.
Several medications and conditions can interfere with this screen. Do not stop blood thinners or other medicines without medical advice. If there is a possible interference, your care team may repeat the test off certain medications or use alternative tests. Discuss your full medication list, recent clots, pregnancy status, and family history so your results can be interpreted accurately.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Heparin, warfarin, and direct oral anticoagulants can alter clotting assays and produce misleading results. Your clinician may time testing around therapy or use drug-neutralizing reagents or alternative methods.
Antiphospholipid antibodies and other coagulation inhibitors can prolong clotting tests and mimic or mask APC resistance. Additional testing may be needed to sort out the cause.
Active clot, recent surgery, infection, or elevated acute phase factors can shift clotting responses. Testing may be deferred or repeated once you are clinically stable.
Underfilled citrate tubes, improper mixing, or delayed processing can affect clotting times. Proper fill volume and timely centrifugation help ensure reliable results.
Estrogen therapy, pregnancy, and the postpartum period change coagulation balance and may influence screening assays. Your clinician may choose confirmatory or genetic testing in these settings.
Conditions that lower multiple clotting factors or alter natural anticoagulants can confound interpretation of APC resistance screens and may require targeted follow-up testing.
References