Diagnostic utility of serum melatonin levels in systemic lupus erythematosus: a case-control study.

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune inflammatory disease and early diagnosis is of clinical and therapeutic importance. Melatonin is an endogenous endolamine hormone that plays an important role in the immune system due to its anti-inflammatory action. This study was designed to assess serum melatonin levels in SLE patients and to evaluate the possible correlation between serum melatonin and patients' baseline characteristics. A case-control study was performed on 50 SLE patients (48 females and 2 males), diagnosed according to the revised 1997 ACR Criteria, and 25 healthy controls (24 females and 1 male), matched by age and sex. Daily serum melatonin levels were investigated in all participants using human melatonin enzyme linked immunosorbent assay (ELISA) kit (MYBIOSOURCE (MBS), United States). Serum melatonin concentration was significantly lower in patients with SLE compared to healthy controls (19.17±6.86 pg/mL vs 23.26±6.71 pg/mL, p=0.017). Serum melatonin concentration ≤18.51 pg/mL was the optimum cut off value to differentiate between SLE patients and healthy controls with an accuracy of 69.3%, a sensitivity of 66%, and a specificity of 76%. The positive predictive value (PPV) at pretest 50% was 73.3% and PPV at pretest 90% was 96.1%; the negative predictive value (NPV) at 10% was 95.3%. Patients' characteristics were not significantly correlated with serum melatonin concentrations using multiple logistic regression analysis. Serum melatonin was a valid measure to differentiate between SLE patients and healthy controls with good accuracy, sensitivity and specificity and PPV and NPV. There was no significant correlation between serum melatonin concentrations and patients' baseline characteristics.