Patients with serologically active but clinically quiet systemic lupus erythematosus remain at high risk of disease flare, with changes in anti-dsDNA antibodies and C3 levels providing valuable early warning of disease reactivation.
Patients with systemic lupus erythematosus who appear clinically well despite persistently abnormal serology may still require close surveillance, with new research showing that changes in two long-established biomarkers can predict impending disease flare.
Researchers, including Melbourne rheumatologist Dr Luigi Zolio, found that almost two-thirds of patients with prolonged serologically active clinically quiescent (SACQ) lupus experienced at least one disease flare during follow-up, while rising immunoglobulin G (IgG) anti-double stranded DNA (anti-dsDNA) antibody levels and falling complement C3 concentrations independently predicted both subsequent flare and sustained disease activity.
Their findings have been published in Rheumatology.
“Most SACQ patients developed clinical flares. Changes in IgG anti-dsDNA and C3 levels emerged as strong predictors of flare in prolonged SACQ patients in a visit-by-visit analysis, supporting close clinical monitoring and highlighting the value of serological trends despite the presence of prolonged clinical quiescence and sustained biomarker abnormalities,” the researchers wrote.
SACQ lupus describes patients who have persistently elevated anti-dsDNA antibodies and/or low complement levels despite having no clinical evidence of active disease.
The condition affects an estimated 6-25% of people with SLE and has long posed a management dilemma, with uncertainty over whether abnormal serology alone should prompt closer monitoring or changes in treatment.
To better define the prognostic value of these biomarkers, the researchers analysed data from the University College London Hospital Lupus Cohort collected between 2020 and 2025.
They identified 60 patients with prolonged SACQ disease, defined as at least six months of persistently elevated IgG anti-dsDNA antibodies, low C3 levels, or both, in the complete absence of clinical activity according to the BILAG-2004 disease activity index.
Patients were followed through 531 clinic visits over a mean of 3.3 years.
By the end of follow-up, 38 patients (63.3%) had experienced at least one clinical flare, accounting for 117 flare episodes overall.
Fifteen patients developed moderate-to-severe flares, while 14 experienced disease activity affecting multiple organ systems simultaneously. The median time to the first flare was approximately 16 months after entering the prolonged SACQ state.
Haematological flares were the most frequent, occurring in almost 42% of patients who flared, followed by musculoskeletal disease (33%), mucocutaneous involvement (25%), and renal flares (13%).
Cardiorespiratory and constitutional flares were uncommon but still occurred despite prolonged periods of apparent clinical remission.
Using longitudinal generalised estimating equation models that assessed biomarker levels at each visit against disease activity at the subsequent visit, the researchers found both biomarkers independently predicted worsening disease.
Every 10IU/mL increase in IgG anti-dsDNA antibody titre increased the odds of a subsequent flare by 4% and increased the odds of sustained disease activity by 8%. The associations were even stronger for moderate-to-severe flares and persistent moderate-to-severe disease activity.
Complement C3 proved an even stronger predictor. Every 0.1g/L reduction in C3 increased the odds of any flare by 25%, moderate-to-severe flare by 39%, sustained disease activity by 23%, and persistent moderate-to-severe disease activity by almost 60%.
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Analysis showed the risk rose sharply once C3 levels fell below 0.9 g/L before plateauing at higher concentrations.
These associations remained significant after adjustment for age, sex, and treatment de-escalation, suggesting the findings reflected genuine disease biology rather than changes in therapy or follow-up schedules.
The researchers also found little evidence that reducing corticosteroids, hydroxychloroquine or immunosuppressive therapy independently explained the increased risk of flare.
Most baseline demographic and clinical characteristics were similar between patients who flared and those who remained clinically quiescent.
However, anti-Ro antibodies were significantly more common among patients who later developed disease activity, suggesting they may represent an additional risk marker – but the authors cautioned that larger studies were needed to confirm this observation.
The findings contrast with earlier studies that failed to show fluctuations in anti-dsDNA antibodies or complement reliably predicted flare in prolonged SACQ lupus.
The researchers said their study’s longitudinal design, frequent serial measurements, and use of the more sensitive BILAG-2004 disease activity index allowed a more accurate assessment of biomarker dynamics than previous analyses based on isolated time points.
They also noted that the high flare rate observed in the cohort suggested prolonged SACQ disease was rarely a benign state.
Rather than representing true remission, persistent serological activity may signal ongoing immunological processes that eventually translated into clinical disease.
“In conclusion, prolonged SACQ patients represent a distinct subgroup of SLE in whom persistent serological activity without clinical manifestations makes flare prediction challenging,” the researchers wrote.
“To our knowledge, this study provides the first longitudinal evidence of a direct correlation between rising IgG anti-dsDNA titres and/or declining C3 levels and subsequent disease activity in this population, supporting their genuine predictive value and providing important insight into its temporal dynamics.
“The high likelihood of developing clinical flares indicates that the SACQ state is significant, and regular monitoring of IgG anti-dsDNA antibodies and C3 levels may support a more personalised and timely approach to disease management, helping to reduce flare-related morbidity and long-term organ damage.”
