Are whole blood hydroxychloroquine blood levels helpful in patients taking chloroquine?  

I could not find anything in the literature, but a personal communication with Dr. Michelle Petri at the Johns Hopkins Lupus Center says that the answer is, "No."

Hydroxychloroquine levels are typically measured by most laboratories using Liquid Chromatography-Tandem Mass Spectrometry technique ( LC-MS). Liquid chromatography distinguishes compounds based on their physicochemical properties and Mass spectrometry uses Mass to charge ratio for the same. The mas...