Monitoring of warfarin/vitamin K antagonists in patients with antiphospholipid syndrome
| Monitoring test . | Type of assay . | Target range . | Points to note . |
|---|---|---|---|
| PT-INR (venous) | Clotting assay INR = PT/MNPT | 2.0-3.0 3.0-4.0 | • Venous (laboratory) INR standard test to monitor VKA anticoagulation intensity in APS patients • Ensure new thromboplastins have low sensitivity to LA before using to monitor VKA • Define MNPT and ISI for reagent/instrument combination • Check baseline PT before anticoagulation, if possible • If baseline PT prolonged, check for acquired factor II deficiency (LA-hypoprothrombinemia syndrome) |
| PT-INR (point-of-care) | Clotting assay INR = PT/MNPT | 2.0-3.0 3.0-4.0 | • Reliable, accurate INRs versus venous INRs in general population • Interpret with caution in APS patients - may be discordant versus venous INRs Pragmatic approach for APS patients: In patients using POC INRs (including self-testing/self-monitoring), via an anticoagulation clinic, ensure: • Check for concordance versus venous INRs (ie, <0.5 INR unit difference) before use for monitoring: initially on three occasions when venous INR in therapeutic range, thereafter, suggest check concordance once every 6-12 months • Regular internal quality control: run at minimum when testing a new batch of test strips or if unexpectedly high or low INR • Regular external quality assessment |
| Chromogenic factor X | Chromogenic assay | ~40%–20% = INR 2.0-3.0 | • LA-independent measure of anticoagulant intensity • Therapeutic ranges not established • Poor utility at INRs >3.0 (equivalent to chromogenic factor X < 12 IU/dL; ie, inverse relationship) • Not widely available or practicable for routine use • Could assist (1) in INR monitoring when prolonged INR before warfarin/VKA; or (2) if recurrent thrombotic event while on apparently therapeutic VKA anticoagulation |
| Thrombin generation | Fluorogenic substrate, continuous measurement of TG | Therapeutic range not established | • ETP and peak TG showed significant inverse correlations with INR in non-APS and APS patients24 • A subgroup of APS patients with increased peak TG, despite therapeutic INR and CFX, suggests that TG might identify an ongoing prothrombotic state24 • The use of TG remains limited to specialized laboratories due to lack of standardization and established therapeutic ranges |
| Monitoring test . | Type of assay . | Target range . | Points to note . |
|---|---|---|---|
| PT-INR (venous) | Clotting assay INR = PT/MNPT | 2.0-3.0 3.0-4.0 | • Venous (laboratory) INR standard test to monitor VKA anticoagulation intensity in APS patients • Ensure new thromboplastins have low sensitivity to LA before using to monitor VKA • Define MNPT and ISI for reagent/instrument combination • Check baseline PT before anticoagulation, if possible • If baseline PT prolonged, check for acquired factor II deficiency (LA-hypoprothrombinemia syndrome) |
| PT-INR (point-of-care) | Clotting assay INR = PT/MNPT | 2.0-3.0 3.0-4.0 | • Reliable, accurate INRs versus venous INRs in general population • Interpret with caution in APS patients - may be discordant versus venous INRs Pragmatic approach for APS patients: In patients using POC INRs (including self-testing/self-monitoring), via an anticoagulation clinic, ensure: • Check for concordance versus venous INRs (ie, <0.5 INR unit difference) before use for monitoring: initially on three occasions when venous INR in therapeutic range, thereafter, suggest check concordance once every 6-12 months • Regular internal quality control: run at minimum when testing a new batch of test strips or if unexpectedly high or low INR • Regular external quality assessment |
| Chromogenic factor X | Chromogenic assay | ~40%–20% = INR 2.0-3.0 | • LA-independent measure of anticoagulant intensity • Therapeutic ranges not established • Poor utility at INRs >3.0 (equivalent to chromogenic factor X < 12 IU/dL; ie, inverse relationship) • Not widely available or practicable for routine use • Could assist (1) in INR monitoring when prolonged INR before warfarin/VKA; or (2) if recurrent thrombotic event while on apparently therapeutic VKA anticoagulation |
| Thrombin generation | Fluorogenic substrate, continuous measurement of TG | Therapeutic range not established | • ETP and peak TG showed significant inverse correlations with INR in non-APS and APS patients24 • A subgroup of APS patients with increased peak TG, despite therapeutic INR and CFX, suggests that TG might identify an ongoing prothrombotic state24 • The use of TG remains limited to specialized laboratories due to lack of standardization and established therapeutic ranges |
ETP, endogenous thrombin potential.
Adapted from Table 1 in Cohen et al.52