{"id":"antithrombin-activity","name":"Antithrombin Activity","shortName":"Antithrombin","aliases":["Antithrombin III","AT III","ATIII","Antithrombin","AT Activity","Antithrombin III Activity","Antithrombin Activity, Plasma","Antithrombin, Enzymatic (Activity)","Antithrombin Activity, Chromogenic","Antithrombin Functional","AT-III","AT3","Antithrombin III (AT3)","Antithrombin Activity, with Reflex to Antithrombin Antigen"],"abbreviations":["AT","AT III","ATIII","AT3"],"loinc":[{"code":"27811-9","primary":true},{"code":"3174-0","primary":false}],"specimen":"plasma","units":[{"ucum":"%","display":"%"}],"referenceRanges":[{"population":"Adults","low":80,"high":130,"unit":"%","unitDisplay":"%","note":"Adult chromogenic-assay interval from Mayo Clinic Laboratories (80–130%). ARUP lists 76–128% for ages 18 and older, and the exact limits depend on the lab's assay (anti-Xa and anti-IIa based tests can differ for some inherited variants). Newborns have lower levels (Mayo: at least 35–40% in full-term babies, reaching adult values by about 90 days). Levels also fall in late pregnancy and the first weeks after delivery (BSH).","sources":[{"title":"Antithrombin Activity, with Reflex to Antithrombin Antigen, Plasma (test AATTF)","url":"https://www.testcatalog.org/show/AATTF","publisher":"Mayo Clinic Laboratories (Extended Catalog)"},{"title":"Antithrombin, Enzymatic (Activity) (ARUP test 0030010)","url":"https://ltd.aruplab.com/Tests/Pub/0030010","publisher":"ARUP Laboratories"},{"title":"Thrombophilia testing: A British Society for Haematology guideline","url":"https://pubmed.ncbi.nlm.nih.gov/35645034/","publisher":"British Journal of Haematology","year":2022},{"title":"Comparison of antithrombin activity assays in detection of patients with heparin binding site antithrombin deficiency: systematic review and meta-analysis","url":"https://pubmed.ncbi.nlm.nih.gov/37794095/","publisher":"Scientific Reports","year":2023}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"Measures how well antithrombin, a natural brake on blood clotting, is working in your blood.","url":"https://bloodtesttracker.com/markers/antithrombin-activity","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}