BackgroundThe aim of this study was to analyze the relationship of the estimated glomerular filtration rate (eGFR) to hydroxychloroquine (HCQ) blood concentrations in systemic lupus erythematosus (SLE) patients.MethodPatients with SLE who had been taking HCQ for more than 12 months were recruited. All subjects gave written informed consent. Various clinical characteristics and laboratory values were examined. The blood concentration of HCQ was measured by high-performance liquid chromatography, and the relationship of eGFR to HCQ blood concentration was mainly investigated.ResultIn total, 115 patients with SLE receiving long-term HCQ therapy were included in the study. The median concentration of HCQ was 1096 ng/ml (range 116–8240 ng/ml). The eGFR was strongly associated with blood concentration of HCQ (P= 0.011,P< 0.05), when adjusted for age, sex, body mass index (BMI), weight-adjusted dose, prednisone use and immunosuppressive drug use. No statistically significant association were found between age, duration, BMI, weight-adjusted HCQ dose, corticosteroid use, immunosuppressant use and blood concentrations of HCQ.ConclusionWe provided novel evidence that impaired renal function influenced the blood concentration of HCQ. Patients with low eGFR need to adjust the HCQ dosage according to the monitoring results of HCQ blood concentrations.Key points• A higher HCQ blood concentration was associated with low eGFR.• This finding reinforces the importance of routine HCQ measurement to maintain normal blood concentrations.• HCQ blood monitoring will be useful for dose modification in patients with renal dysfunction.