Hypercoagulable States - Inherited Thrombophilias, When to Test, and Antiphospholipid Syndrome

A young woman turns up with a proximal leg DVT and no surgery, no trauma, no cancer and no immobility - just six months of a combined oral contraceptive and a family history of clots. This is the full walkthrough of how to think about a hypercoagulable state. A comprehensive resident lecture on the natural anticoagulant brakes, the inherited thrombophilia table, when a thrombophilia panel is worth sending, and antiphospholipid syndrome from the revised Sapporo criteria through catastrophic disease. What you'll learn: • The three brakes on coagulation - tissue factor pathway inhibitor, antithrombin (accelerated roughly a thousandfold by heparin), and thrombin-thrombomodulin activation of protein C with protein S as cofactor • Why factor V Leiden (Arg 506 Gln, about 5 percent prevalence, relative risk about 5) and prothrombin G20210A (2 percent, relative risk about 4) are common and weak, while protein C, protein S and antithrombin deficiency are rare and carry relative risks above 20 • Why testing at the moment of the clot misleads - consumption during acute thrombosis, warfarin lowering protein C and S, heparin lowering antithrombin - and why the question is revisited at three to six months • How the site of the clot directs the acquired workup: splanchnic or cerebral venous sinus toward myeloproliferative neoplasm (JAK2 V617F) and PNH (CD55 and CD59), arterial toward antiphospholipid syndrome, plus the roughly 4 percent occult cancer yield and the absence of benefit from routine abdominal and pelvic CT • The revised Sapporo criteria - one clinical plus one laboratory criterion, the same antibody positive twice at least twelve weeks apart, titers above 40 units and IgG weighted over isolated IgM - and the APS anticoagulation rules the source teaches: heparin to warfarin, lifelong for most, warfarin preferred over a DOAC in triple positive patients, INR 2 to 3, with or without aspirin 81 mg daily for arterial events, and prompt triple therapy in catastrophic APS Key takeaway: A thrombophilia lowers the threshold rather than causing the clot - treat the thrombosis by the venous thromboembolism pathway first, and let the testing question wait until three to six months, when the answer can actually change something. Chapters: 0:00 The unprovoked clot 1:08 Learning objectives 2:50 Exam and the initial workup 4:30 The brakes on coagulation and factor V Leiden 5:50 The prothrombin G20210A variant 7:05 Antithrombin deficiency and heparin resistance 8:53 Common and weak, rare and strong 9:59 The search for an occult cancer 11:08 When testing might change something 12:43 The patient who has already clotted 13:50 A second patient 15:02 The thrombotic criterion 16:08 The laboratory criteria 17:18 What the antibody actually does 19:01 Treating antiphospholipid syndrome 20:10 Catastrophic antiphospholipid syndrome 21:21 Pitfalls 22:31 Summary and references Part of Teaching Service — Hospital Rounds: education for residents and advanced practice providers. For clinician and trainee education only. Not medical advice; verify against current guidelines and institutional protocols before applying to patient care. #Thrombophilia #FactorVLeiden #AntiphospholipidSyndrome #Hypercoagulable #DVT #VTE #ProteinCDeficiency #Antithrombin #Hematology #MedicalEducation