SF receiver operating characteristic area under the curve. SF ROC AUC for iron load determined by (A) TIL, (B) TIL limited to measures more than 50 mg/kg, or (C) LIC. Circles represent averages of 1000 random data sampling; bars, SD. ROC AUC represents the area under the curve of sensitivity plotted against 1 − specificity for all possible SF values for a given iron load level. The closer ROC AUC equals 1, the better SF is, as a discriminator of iron; the closer ROC AUC equals 0.5, the closer SF is to random.²¹