IRON/IRON BINDING CAPACITY - serum

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Specimen: 5 mL blood in plain or tube.

Method:

Iron - spectrophotometry.

Iron binding capacity - immunoassay of transferrin with expression of the result in µmol/L. Iron binding capacity is 2 x transferrin concentration. The spectrophotometric assay for iron binding capacity is no longer used.

Transferrin saturation - iron/iron binding capacity expressed as a decimal or as a percentage.

Reference Interval:

Iron:	10-30 µmol/L
Iron binding capacity:	45-80 µmol/L
Transferrin saturation:	0.15-0.45 (15-45%)
Transferrin:	1.7-3.0 g/L

Application: Investigation of suspected iron deficiency or iron overload; serum ferritin is the preferred method for assessing iron stores. See FERRITIN . The tests are not appropriate and may be misleading in patients receiving iron therapy. Assessment of patients with acute iron poisoning.

Interpretation: This may be complicated by the presence of an acute phase response, which is associated with decreased iron and iron binding capacity (with increased ferritin). Hepatocellular disease can have a similar effect. As iron deficiency may co-exist with an acute phase response, assessment of the haemoglobin response to iron therapy offers an alternative, cost effective approach. See Table 3 . In acute iron poisoning, iron levels are often >60 µmol/L, with transferrin saturation ³100%. Toxicity can occur with lower levels if absorption is continuing at the time of specimen collection.

Reference: Gordeuk VR et al. Crit Rev Clin Lab Sci 1996; 33: 39-82. Guyatt GH et al. J Gen Intern Med 1992; 7: 145-153.

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