Abstract Number: PB1056
Meeting: ISTH 2021 Congress
Background: ISTH APS guidelines recommend two lupus anticoagulant (LA) reagent systems: the dilute Russell’s Viper Venom Time (DRVVT) and a LA-sensitive aPTT-like assay. Other LA reagents are available, including the dilute prothrombin time (DPT). At UChicago Medicine, we provide a comprehensive APS panel that includes lupus-sensitive aPTT, DRVVT, as well as the DPT LA assay. In combination with the DRVVT, the DPT can serve as an effective screen for confounding anticoagulant medications such as warfarin and Xa inhibitory DOAC.
Aims: Here we analyze the utility of DPT-based functional LA testing in contributing laboratory evidence of antiphospholipid syndrome as well as in assisting with interpretation of LA panels.
Methods: We retrospectively evaluated all lupus anticoagulant testing in a 4.5 year period (1693 patients, 2015 cases). DPT positivity was defined as a prolonged screening clotting time and a significant shortening of clotting time with high concentration phospholipid, in keeping with ISTH guidelines.
Results: Of the 2015 cases evaluated, DPT was generally positive in concert with other LA studies (Table 1). Only 56 cases showed sole LA positivity in the DPT-based system (2.8%). In only two cases was repeat LA testing performed and the DPT the only functional system that contributed confirmatory repeat laboratory evidence of antiphospholipid syndrome.
Warfarin and Xa inhibitory DOACs are common causes of interference with DRVVT testing. Prolonged DPT screens with negative confirmatory phase are commonly seen with these anticoagulants. Warfarin interference leads to DPT screen > DRVVT screen while Xa inhibitory DOAC lead to the opposite pattern (Table 2). These cases receive extra pathologist scrutiny for possible false positive DRVVT.
Table 1 | Total DPT Testing (2015 total screens) | ||
Number | Percent of total | Percent of subgroup | |
Prolonged DPT screen | 1154 | 57.3% | |
Abnormal DPT confirm | 213 | 10.6% | |
Abnormal DPT confirm cases with other positive lupus anticoagulant studies (DRVVT, aPTT) | 157 | 7.8% | 73.7% of abnormal DPT confirm |
Abnormal DPT confirm cases with no other positive lupus anticoagulant studies | 56 | 2.8% | 26.3% of abnormal DPT confirm |
Abnormal DPT confirm with no other positive lupus anticoagulant studies and with clinical evidence of APS | 27 | 1.3% | 50.0% of abnormal DPT confirm cases with no other positive lupus anticoagulant studies and available clinical data |
Table 2 | |||
Number | Percent of total DPT testing (2015 total screens) | ||
Cases with abnormal DRVVT confirm | 653 | 32.4% | |
– with prolonged DPT screen but negative DPT confirm | 371 | 18.4% | |
– with DPT screen > DRVVT screen | 229 | 11.4% | |
– with DRVVT screen > DPT screen | 139 | 6.9% |
Conclusions: The DPT is only rarely the sole positive LA system.
In combination with the DRVVT, the DPT can serve as an effective screen for anticoagulant interference and contributes to the accuracy of pathologist interpretation of APS panels.
To cite this abstract in AMA style:
Storozuk T, Wool G. The Utility of the Dilute Prothrombin Time Assay in the Diagnosis of Antiphospholipid Syndrome [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/the-utility-of-the-dilute-prothrombin-time-assay-in-the-diagnosis-of-antiphospholipid-syndrome/. Accessed March 22, 2024.« Back to ISTH 2021 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/the-utility-of-the-dilute-prothrombin-time-assay-in-the-diagnosis-of-antiphospholipid-syndrome/