The values of area under the curves (AUC) for the prediction of hyponatremia in children with SLE were 0.749 (95% CI 0.589–0.908, p = 0.026) for high SLEDAI, 0.779 (95% CI 0.613–0.946, p = 0.012) for high ESR levels, 0.775 (95% CI 0.599–0.951, p = 0.013) for high AST levels, 0.758 (95% CI 0.563–0.953, p = 0.021) for decreased serum C3 levels and 0.778 (95% CI 0.650–0.906, p = 0.013) for decreased serum albumin levels. The gene discussed is C3; the disease is systemic lupus erythematosus.