Transferrin Saturation of 20% in a 9-Year-Old Child
A transferrin saturation of 20% in this child with normal ferritin, normal serum iron, normal inflammatory markers, and mildly elevated TIBC represents the lower limit of normal and does NOT definitively indicate early iron deficiency. 1, 2, 3
Age-Specific Interpretation of Transferrin Saturation
Children aged 0.5-12 years have significantly lower transferrin saturation values than adults, with normal ranges extending well below the adult threshold of 20-50%. 1, 3
In healthy, iron-replete children (ferritin ≥15 μg/L), 19.9% had transferrin saturation values below 15%, and 8.2% had values below 10%, demonstrating that low TSAT is common in normal children. 2
The 2.5th percentile for transferrin saturation in iron-replete children is only 5%, meaning values as low as 5% can still be normal. 2
A transferrin saturation below 16% in children aged 0.5-12 years constitutes evidence of iron deficiency ONLY when accompanied by anemia and low mean corpuscular volume, not as an isolated finding. 3
Clinical Context of This Case
Normal ferritin excludes depleted iron stores, as ferritin is the most specific indicator of iron stores and would be low (<30 ng/mL) in true iron deficiency. 4, 1
Normal serum iron argues against iron-deficient erythropoiesis, as serum iron decreases when iron availability for red blood cell production is inadequate. 4, 1
Normal inflammatory markers exclude functional iron deficiency, which occurs when inflammation (elevated CRP/ESR) causes hepcidin to trap iron in storage sites despite adequate stores. 4, 1
The mildly elevated TIBC reflects increased transferrin synthesis, which can be a normal physiologic response during growth spurts in children rather than pathologic iron deficiency. 5, 6
Diagnostic Threshold Considerations
In adults without inflammation, TSAT <16% confirms iron deficiency, but this threshold does not apply to children due to developmental differences. 4, 1
In inflammatory conditions, TSAT <20% is used as the diagnostic threshold, but this child has normal inflammatory markers, making this criterion irrelevant. 1
For children specifically, transferrin saturation is unsuitable as a single diagnostic criterion and should always be combined with other indicators of iron status including ferritin, hemoglobin, and MCV. 2
Physiologic Changes During Growth
During pubertal development, serum transferrin increases and ferritin decreases as iron redistributes from stores to expanding red blood cell mass, which can lower TSAT without indicating true deficiency. 5, 6
The transferrin receptor-ferritin ratio is more sensitive than TSAT alone for detecting tissue iron deficiency in growing children, though it was not measured in this case. 6, 7
Clinical Recommendation
No intervention is warranted at this time. 2, 3 This child's TSAT of 20% sits at the lower limit of normal for age, but the constellation of normal ferritin, normal serum iron, and absence of anemia or microcytosis indicates adequate iron status. 1, 2, 3
Monitoring Strategy
Recheck complete blood count to confirm normal hemoglobin and MCV, as iron deficiency in children requires the triad of low TSAT, anemia, and low MCV. 3
If hemoglobin and MCV are normal, reassess iron parameters in 3-6 months to ensure stability during ongoing growth. 1
Consider measuring soluble transferrin receptor or sTfR/ferritin ratio if clinical suspicion for early iron deficiency persists despite normal standard parameters, as these are more sensitive in children. 4, 7
Common Pitfalls to Avoid
Do not apply adult TSAT thresholds to children, as this leads to overdiagnosis of iron deficiency and unnecessary iron supplementation. 2, 3
Do not interpret TSAT in isolation—always integrate ferritin, hemoglobin, MCV, and inflammatory markers to avoid misdiagnosis. 1, 2
Do not overlook normal physiologic changes during growth, when transferrin rises and ferritin falls as part of healthy iron redistribution to support expanding blood volume. 5, 6