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 mass spectrometer, at least in principle can detect the species conforming to each chromatographic peak through its unique mass spectrum, minimizing the need to chromatographically separate isotopic or mass-differentiated isobaric components. It is this dual selectivity that makes LC-Mass Spectrometry such a powerful analytical tool for separation, detection, and quantitation.

• Chloroquine (C₁₈H₂₆CLN₃) , Molecular weight 319.9, less soluble.
• Hydroxy...