Background/Purpose Remission and low disease activity (LDA) are associated with decreased flares, damage, and mortality. However, little is known about the impact of disease activity states (DAS) on health care costs. We determined the independent impact of different definitions of remission and LDA on direct and indirect costs (DC, IC) in a multicentre, multi- ethnic inception cohort.
Methods Patients fulfilling revised ACR classification criteria for SLE from 33 centres in 11 countries were enrolled within 15 months of diagnosis and assessed annually. Patients with ≥2 annual assessments were included. Five mutually independent DAS were defined:
1) Remission off-treatment: clinical (c) SLEDAI-2K=0, without prednisone or immunosuppressants
2) Remission on-treatment: cSLEDAI-2K=0, prednisone ≤5mg/d and/or maintenance immunosuppressants
3) LDA-Toronto Cohort (TC): cSLEDAI-2K≤2, without prednisone or immunosuppressants
4) Modified Lupus LDA State (mLLDAS): SLEDAI-2K≤4, no activity in major organs/systems, no new disease activity, prednisone ≤7.5mg/d and/or maintenance immunosuppressants
5) Active: all remaining assessments
Antimalarials were permitted in all DAS. At each assessment, patients were stratified into 1 DAS; if >1 definition was fulfilled per assessment, the patient was stratified into the most stringent. The proportion of time patients were in a specific DAS at each assessment since cohort entry was determined.
At each assessment, annual DC and IC were based on health resource use and lost workforce/non-workforce productivity over the preceding year. Resource use was costed using 2021 Canadian prices and lost productivity using Statistics Canada age-and-sex-matched wages.
To examine the association between the proportion of time in a specific DAS at each assessment since cohort entry and annual DC and IC, multivariable random-effects linear regression modelling was used. Potential covariates included age at diagnosis, disease duration, sex, race/ethnicity, education, region, smoking, and alcohol use.
Results 1631 patients (88.7% female, 48.9% White, mean age at diagnosis 34.5) were followed for a mean of 7.7 (SD 4.7) years (table 1, Panel A). Across 12,281 assessments, 49.3% were classified as active (table 1, Panel B). Patients spending <25% vs 75-100% of their time since cohort entry in an active DAS had lower annual DC and IC (DC $4042 vs $9101, difference - $5060, 95%CI -$5983, -$4136; IC $21,922 vs $32,049, difference -$10,127, 95% -$16,754, - $3499) (table 2, Panel B&C).
In multivariable models, remission and LDA (per 25% increase in time spent in specified DAS vs active) were associated with lower annual DC and IC: remission off-treatment (DC -$1296, 95%CI -$1800, -$792; IC -$3353, 95%CI -$5382, -$1323), remission on-treatment (DC -$987, 95%CI -$1550, -$424; IC -$3508, 95%CI -$5761, -$1256), LDA-TC (DC -$1037, 95%CI -$1853, -$222; IC -$3229, 95%CI -$5681, -$778) and mLLDAS (DC -$1307, 95%CI -$2194, -$420; IC - $3822, 95%CI -$6309, $-1334) (table 3, Model B). There were no differences in costs between remission and LDA.
Conclusions Remission and LDA are associated with lower costs, likely mediated through the known association of these DAS with more favourable clinical outcomes.
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