HCQ Blood Level Monitoring — SCE Rheumatology MCQ

Correct answer: E — Whole-blood concentrations can assess adherence and drug exposure and may support individualised dosing, but universal routine monitoring and improved outcomes from concentration-guided escalation are not established.

Whole-blood HCQ measurement provides an objective assessment of exposure and is useful when non-adherence, pharmacokinetic variability or inadequate response is suspected. Levels below 200 ng/mL strongly suggest severe non-adherence. Recent observational evidence proposes an emerging reference range of 750 to less than 1150 ng/mL, but this has not established mandatory routine testing. EULAR supports selected use to assess adherence or guide individualised dosing where available. Importantly, the PLUS randomised trial did not show that concentration-guided dose escalation reduced flares. Serum and whole-blood values are not interchangeable using the same thresholds, and blood testing does not replace retinal screening. A concentration below 750 ng/mL does not by itself prove complete non-adherence, while aiming above 1200 ng/mL is unsupported and may increase toxicity risk.

Reference: Fanouriakis A et al. EULAR recommendations for the management of systemic lupus erythematosus: 2023 update, hydroxychloroquine recommendation. Annals of the Rheumatic Diseases, 2023. https://pubmed.ncbi.nlm.nih.gov/40746405/