We congratulate Jensen et al on their paper entitled “Post-natal serum Insulin-like Growth Factor one and retinopathy of prematurity” published in Retina 2016:0:1–61 particularly with their attempts to assess whether IGF-1 estimation in predicting retinopathy of prematurity (ROP) is useful in a racially diverse U.S. cohort. Interestingly, we found the utility of IGF-1 to be race specific in our racially diverse U.K. cohort and not so useful in babies with black mothers.2 The mean values of serum IGF-1 levels (μg/L) from the U.K. cohort are remarkably similar to the United States and different from Hellstrom et al's cohort as illustrated in the Table 1.
To address the different conclusions, we would like to ask for further information regarding three points.
Our cohort of black babies had significantly lower IGF-1 levels at 32 weeks to 33 weeks compared with non-black babies despite none of them needing treatment. Maybe the IGF-1 levels did not rise to a threshold level and therefore did not trigger the proliferative phase.
The difference between the two groups (no retinopathy of prematurity and severe retinopathy of prematurity) in the United States was less than the Scandinavian cohort. Although the reported 3 μg/L difference in IGF-1 might be statistically significant, it may be of little practical use.