Filter paper–based insulin-like growth factor assay

This study assessed validity, reliability, and feasibility of a filter paper blood spot insulin-like growth factor 1 (IGF-1) assay for retinopathy of prematurity (ROP) research. Blood samples were collected from 45 healthy children. Half of each sample was spun to obtain serum; half was applied to filter cards and stored for varying times and at different temperatures. IGF-1 assays were performed using a commercially available kit. Intraclass correlation between blood spot and serum IGF-1 values was high (0.97) for validity, and the mean differences were low for test-retest reliability. Time (up to 25 days) and temperature (4° C to 37° C) had no significant effect on sample stability. Feasibility was further assessed in a second cohort study of 74 premature infants being screened for ROP. A total of 817 filter card samples were successfully collected and transported to a central lab, where IGF-1 assays were successfully performed.