SFTPD and systemic sclerosis: Most studies investigating SP‐D in association with CTD‐ILD have assessed patients with systemic sclerosis (SSc).21, 22 Serum SP‐D levels in patients with SSc are significantly higher than in healthy controls, and serum SP‐D levels in patients with systemic sclerosis‐associated ILD (SSc‐ILD) are significantly higher than in patients without SSc‐ILD.