This assay measures the whole blood concentration of hydroxychloroquine. Monitoring HCQ may improve adherence, and whole blood HCQ concentrations may be useful in titrating dose to achieve maximal clinical benefit in lupus while minimizing long-term retinal toxicity in lupus and other chronic autoimmune diseases.

In lupus, RA and other autoimmune diseases, several weeks or months may be required to reach maximum therapeutic benefit that correlates with whole blood HCQ measurement.

This test should be ordered after 3 - 6 months of daily HCQ to assess daily dosage in lupus, RA and other autoimmune diseases.

Lavender (EDTA), 4mL

Immediately following collection, mix sample thoroughly by gentle inverting 8 - 10 times, to prevent clotting

Lavender (EDTA), 4mL

Refrigerated (preferred) – 15 days

Ambient – 15 days

Frozen – NO

• Frozen specimen

Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS)

Quantitation Limit: 25 ng/mL

Results of 25 or higher indicate detection of hydroxychloroquine in whole blood.

Interpretive Comments:

• A threshold target whole blood HCQ concentration of 1000 ng/mL has been studied in lupus ¹.
•  Concentrations less than 200 ng/mL denote non-compliance and risk of flare in lupus ¹.
• Levels of 500 ng/mL or more are consistent with adherence ².
•  The anti-inflammatory action of HCQ appears to be cumulative, and clinical efficacy in autoimmune diseases takes as long as 3 - 6 months ^3,4.
•  Higher whole blood (WB) HCQ concentrations were predictive of later retinopathy in 492 systemic lupus erythematosus patients. Patients in the highest tertile (mean WB HCQ ranging from 1177 to 3514 ng/mL) had the highest incidence of retinal toxicity (13%)⁵.
•  Less retinopathy (2% and 6%) occurred with lower WB HCQ (in tertiles, 0 - 741 and 741.5 - 1176.5 ng/mL, respectively)⁵.
•  The whole blood concentration to serum or plasma concentration ratio is approximately 5³.

References:

1. Costedoat-Chalumeau N, et al. J Rheumatol 2015;42;1997-1999.
2. Durcan L et al. J Rheumatol. 2015;42(11):2092-7.
3. Plaquenil package insert, 2017.
4. Browning. Hydroxychloroquine and Chloroquine Retinopathy. New York, Springer, 2014.
5. Petri M et al. Arthritis Rheumatol. 2020 Mar;72(3):448-453.