{"id":"protein-s-free-antigen","name":"Protein S, Free Antigen","shortName":"Free Protein S","aliases":["Protein S, Free","Free Protein S Antigen","Free Protein S","Protein S Free Ag","Protein S Antigen, Free","Protein S Free, Antigen","Protein S Ag, Free, P","Protein S Ag Free","Free Protein S Ag","PRO S FREE"],"abbreviations":["Free PS","PS free"],"loinc":[{"code":"27821-8","primary":true},{"code":"4677-1","primary":false}],"specimen":"plasma","units":[{"ucum":"%","display":"%"},{"ucum":"[IU]/dL","display":"IU/dL"}],"referenceRanges":[{"population":"Men, 18+","low":74,"high":147,"unit":"%","unitDisplay":"%","note":"ARUP Laboratories interval for males 18 and over (latex immunoassay). Indiana University Health lists 59–118% for both sexes. Mayo Clinic Laboratories' thrombophilia profile follows up a free protein S antigen under 65% (men) with a total protein S antigen test. Use the range printed on your own report.","sources":[{"title":"Protein S Free, Antigen (test 0098894)","url":"https://ltd.aruplab.com/Tests/Pub/0098894","publisher":"ARUP Laboratories"},{"title":"Thrombophilia Profile, Plasma and Whole Blood (test ID AATHR)","url":"https://www.testcatalog.org/show/AATHR","publisher":"Mayo Clinic Laboratories (Extended Catalog, via testcatalog.org)"},{"title":"Thrombosis & Hemostasis Reference Ranges (updated 1/11/2021)","url":"https://cdn.iuhealth.org/resources/Thrombosis-Hemostasis-Ref-Ranges-No-StarMax.pdf","publisher":"Indiana University Health Pathology Laboratory","year":2021}]},{"population":"Women, 18+","low":55,"high":123,"unit":"%","unitDisplay":"%","note":"ARUP Laboratories interval for females 18 and over (latex immunoassay). Indiana University Health lists 59–118% for both sexes. Mayo Clinic Laboratories' thrombophilia profile follows up a free protein S antigen under 65% for women 50 and over and under 50% for women under 50 with a total protein S antigen test. Pregnancy and estrogen-containing medicines lower protein S, and this range is for people who are not pregnant. Use the range printed on your own report.","sources":[{"title":"Protein S Free, Antigen (test 0098894)","url":"https://ltd.aruplab.com/Tests/Pub/0098894","publisher":"ARUP Laboratories"},{"title":"Thrombophilia Profile, Plasma and Whole Blood (test ID AATHR)","url":"https://www.testcatalog.org/show/AATHR","publisher":"Mayo Clinic Laboratories (Extended Catalog, via testcatalog.org)"},{"title":"Thrombosis & Hemostasis Reference Ranges (updated 1/11/2021)","url":"https://cdn.iuhealth.org/resources/Thrombosis-Hemostasis-Ref-Ranges-No-StarMax.pdf","publisher":"Indiana University Health Pathology Laboratory","year":2021}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"Measures the active, unbound form of protein S, a natural blood thinner. It is the test many labs use first to look for low protein S.","url":"https://bloodtesttracker.com/markers/protein-s-free-antigen","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}