All used immunoenzymatic quantification of circulating SP-D, yet inter-assay heterogeneity persisted: three employed sandwich ELISAs (Hycult, BioVendor) with detection limits 1.5–5.0 ng/mL1, whereas the influenza study utilised a high-throughput Luminex platform calibrated to an in-house recombinant standard. The gene discussed is SFTPD; the disease is influenza.