Background/Purpose: SLE patients with persistent lupus anticoagulant (LAC) have been observed to be at significantly higher risk of thrombosis.  A common clinical definition of persistent  LAC is to have two confirmed tests for LAC separated in time by at least 12 weeks.  The likelihood of identifying a patient with LAC based on this definition depends on the frequency with which it is assessed. The purpose of this analysis is to determine the impact of frequent repeated testing of LAC on patient identification and clinical outcomes.

Methods: LAC was measured repeatedly in patients in a large American clinical cohort of prevalent and incident SLE patients. (51% Caucasian-American, 40% African American) . Patients were defined as LAC positive at a clinic visit if they had a dRVVT of 45 or more seconds, a mixing study, and then a positive confirmatory test.  For 20% of the patients, the confirmatory test was missing and these values were imputed using multiple imputation based largely on the value of dRVVT.  Persistent lupus anticoagulant was defined as having two consecutive visits with confirmed lupus anticoagulant separated by at least 12 weeks. We determined the number of patients who would be identified as having persistent LAC under two scenarios: 1) if only 5 LAC assessments were made, or 2) if multiple repeated assessments were made.  In addition, we determined whether those identified with persistent LAC based on multiple repeat assessments but who were not identified based on only 5 assessments were at increased risk of thrombosis.  This was based on discrete survival analysis including followup that occurred after at least 5 LAC assessments was included.

Results: The analysis was based on 36,218 clinical tests of LAC from 1457 different patients who had at least 5 LAC tests.  The number of tests per patient ranged from 5 to 74 with a mean of 25.  Based on only the first 5 tests per patient, the prevalence  of persistent LAC was 11.7%.  Based on all the LAC tests, the prevalence of persistent LAC was found to be 15.8%.  Table 1 shows the rates of thrombosis in months defined by LAC classification based on all prior tests.  In those months that were not preceded by persistent LAC the rate of thrombosis was 1.3 per 1000 person-months.  In those months that were preceded by a diagnosis of LAC based on the patient’s first 5 LAC tests, the rate of thrombosis was 2.5 per 1000 person-months (p=0.018 relative to months without LAC).  In those months that were not classified as having prior persistent LAC based on the patient’s first 5 LAC tests, but were classified as having persistent LAC based on all prior LAC tests, the rate of thrombosis was 1.8 per 1000 person months (p=0.46 relative to months without LAC).

Conclusion: 26% of those with persistent LAC are missed if LAC assessment is based only on the first 5 LAC tests. However, those classified as having LAC based on their first 5 tests are at highest risk of thrombosis.  This information can inform decision-making related to frequency of LAC testing.

Table 1

« Back to 2019 ACR/ARP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/how-often-should-sle-patients-be-tested-for-lupus-anticoagulant/