Rationale and methodology
Planning group member Medha Barbhaiya, MD, MPH, an attending physician at the Hospital for Special Surgery and assistant professor at Weill Cornell Medicine in New York, explained the rationale for the update. “The existing criteria were drafted in 1999 and updated in 2006 and require one clinical criterion, either vascular thrombosis event or pregnancy morbidity along with antiphospholipid antibodies,” she said.
Those 16-year-old criteria also ignored heterogeneous manifestations such as heart valve disease or thrombocytopenia, failed to stratify thrombotic events as risk factors, and used an outdated definition of pregnancy morbidity related to APS, she said.
“These findings helped to support our rationale for new criteria development, along with the fact that over the last 1 to 2 decades there have been important advancements in the methodology of classification criteria development,” she said. ACR and EULAR both endorsed the new methodology for developing the classification criteria, Dr. Barbhaiya added.
That methodology involved multidisciplinary international panels of experts and data-driven efforts, with the goal of identifying patients with a high likelihood of APS for research purposes. The planning group collected 568 cases from 29 international centers, dividing them into two validation cohorts of 284 cases each.
How classification criteria work
Doruk Erkan, MD, MPH, coprincipal investigator representing the United States on the planning group, an attending physician at the Hospital for Special Surgery in New York, and a professor at Weill Cornell Medicine in New York, explained how the classification system works. “If you have a patient that you are considering for APS classification, the story starts with entry criteria, which are one documented clinical criterion plus a positive aPL [antiphospholipid] test within 3 years of observation of the clinical criteria,” he said.
Once the entry criteria for APS are met, there are the clinical and laboratory domains. Dr. Erkan explained that weighted point values are assigned to individual categories under each domain. For example, in the macrovascular VTE domain, VTE with a high VTE risk profile is worth 1 point, but VTE without a high VTE risk profile is worth 3 points.
“APS classification will be achieved with at least three points from clinical domains and at least three points from the laboratory domains,” he said.
The planning group conducted a sensitivity and specificity analysis of the draft classification system using the two validation cohorts. “Our goal was very high specificity to improve the homogeneity in APS research, and we achieved this in both cohorts with 99% specificity,” Dr. Erkan said. That compares to sensitivity of 91% and 86% of the Sapporo criteria in the validation cohorts.
“Our sensitivity was 83% and 84% capturing a broad spectrum of patients assessed with APS suspicion,” he added, vs. 100% and 99% with the Sapporo criteria.
These criteria are not absolute and are structured to permit future modifications, Dr. Erkan said. “When this work is completed, another chapter will start,” he said. “If a case doesn’t meet APS classification criteria, the case may still be uncertain or equivocal rather than not APS. Uncertain or controversial cases should be studied separately to guide future updates of the new criteria.”