Table 1.
Serum biomarkers for iron deficiency anemia in CKD
| Name | Measures (U) | Relation to Iron Deficiency | Treatment Targeta | Predicts Response to IV Iron | Sensitivity/Specificity for Iron Deficiencyb | Drawbacks |
|---|---|---|---|---|---|---|
| Ferritin | Level of ferritin in the blood (ng/dl) | Decreases (<100 ng/dl diagnostic in nondialysis-dependent CKD, <200 ng/dl diagnostic in CKD) | Uncertainc | Not reliable | <100 ng/dl: 35%/78%31 | Acute-phase reactant, elevations not solely related to iron status and upper limit of normal unclear |
| <200 ng/dl: 41%/100%27 | ||||||
| <500 ng/dl: 81%/27%42 | ||||||
| TSAT | Amount of iron bound to transferrin compared with total body stores (%iron/TIBC) | Decreases (<20% diagnostic) | 30%–50% | <30% Predictive | <20%: 63%/80%21 | TIBC affected by inflammation and malnutrition |
| CHr | Absolute amount of Hgb in circulating reticulocytes (pg) | Not reflective of stores | Not established | <29 pg predictive, more effective marker than ferritin or TSAT | 57%/93%31 | Time sensitive to maturation of reticulocytes |
| HRC% | Concentration of Hgb in RBCs (% relative Hgb content relative to RBC size) | Not reflective of stores | Not established | >6% predictive | 82%/95%31 | Must be measured within 6 h of collection |
| sTfR | Transferrin receptors shed from the RBC surface | May increase, can potentially note iron stores | Not established | >1.5 mg/L predictive | 81%/71%31 | Less reliable than CHr and HRC%, may rise in the setting of EPO |
| Hepcidin | Level of hepcidin in blood | Increases | Not applicable | Not reliable | Not applicable | — |
| Plasma NGAL | Level of NGAL in blood (ng/ml) | Increases | Not established | ≤394 ng/ml | 84%/50%42 | — |
TIBC, total iron binding capacity.
a
Thresholds take into account current evidence and are recommended based on these data.
b
Sensitivity/specificity measurements are best estimates, but comparisons across biomarkers are difficult because most studies were done in sample sizes of <100 patients and used different standards of comparison or diagnostic criteria (e.g., bone marrow stores versus response to iron).
c
Current recommendations 200–800 ng/dl and consider supplementation based on risk-benefit analysis for values ≥800 ng/m.