Until recently, the soluble transferrin receptor (sTfR) was the best parameter in assessing iron deficiency in cystic fibrosis, based on which the sTfR (μg/mL) to the logarithm of serum ferritin (mg/L) (TfR/logFer) ratio is calculated, as these values are not inflammation-dependent [10]. Here, TFRC is linked to cystic fibrosis.