Different Control Populations May Lead to Different Understanding of Hydroxychloroquine Blood Levels as a Risk Factor for Retinopathy: Comment on the Article by Petri et al.

We read with great interest the article by Petri et al. describing the association between hydroxychloroquine (HCQ) blood level and HCQ retinopathy in systemic lupus erythematosus (SLE) (1). Retinopathy occurred in 4.3% of 537 SLE patients. Both mean (p=0.0124) and maximum (p=0.034) HCQ blood levels predicted HCQ retinopathy. By contrast, in a recent case-control study including 23 SLE patients with HCQ retinopathy and 547 controls, no association was found between HCQ blood levels and HCQ retinopathy (2) with a median HCQ blood level of 944ng/mL in the retinopathy group versus 849ng/mL in the control group (p=0.46).