TABLE 4.
Approaches to express and interpret the ratio of sTfR to SF1
| Ratio | Calculation | sTfR assay used to establish ratio | Cutoff value and definition |
| Total body iron,2 mg/kg | − [log(sTfR/SF) − 2.28229]/0.1207 | In-house ELISA that is equivalent to Ramco assay and has known relation to Roche assay | ≤0: iron deficit>0: iron surplus |
| Simple ratio2 | sTfR/SF | In-house ELISA that is equivalent to Ramco assay and has known relation to Roche assay | ≤500: ample iron stores>500: depleted iron stores |
| sTfR index, mg/L | sTfR/log SF | First ELISA from R&D Systems; then adopted on Access Beckman Coulter analyzer | <1: ACD>2: IDA or IDA + ACD |
1
ACD, anemia of chronic disease; ELISA, enzyme linked immnosorbent assay; IDA, iron deficiency anemia; IDA + ACD, combined iron deficiency anemia and anemia of chronic disease; SF, serum ferritin; sTfR, soluble transferrin receptor.
2
Units of both sTfR and SF in the ratio are μg/L.