Iron studies

Keywords: Fe studies

Specimen:

5 mL blood in lithium heparin or plain tube.

Method:

See Ferritin, Soluble transferrin receptor.

Application:

Suspected iron deficiency, iron overload, acute iron poisoning (see Iron toxicity). The assessment of iron deficiency or overload may be complicated by the presence of an acute phase response or hepatocellular disease. In general, serum ferritin is the preferred test for the assessment of iron deficiency, however levels may be normal (up to 100 µg/L) when iron deficiency coexists with an acute phase response. Soluble transferrin receptor levels are not affected in an acute phase response; levels are normal in anaemia of chronic disease uncomplicated by iron deficiency. An alternative approach to the patient with suspected iron deficiency and/or chronic inflammatory disease is to assess the haemoglobin response to iron therapy.

Interpretation:

Serum ferritin levels ≥30 µg/L up to the method-related upper reference limit demonstrates healthy iron stores as long as co-existing inflammatory disease or hepatocellular damage are not present.

A serum ferritin level ≤20 µg/L for pre-pubescent children (with or without anaemia) is diagnostic of iron deficiency.

A serum ferritin level <30 µg/L for an adult is diagnostic of iron deficiency.
Serum ferritin levels of 20-60 µg/L in an anaemic pre-pubescent child may represent iron deficiency if there is coexisting inflammatory disease.

Serum ferritin levels of 30-100 µg/L in an anaemic adult may represent iron deficiency if there is coexisting inflammatory disease. In these cases the ratio of ferritin to soluble transferrin receptors gives better discrimination.

An elevated ferritin concentration above the method-related upper reference limit may be due to concurrent inflammatory disease, liver disease or iron overload (Hereditary haemochromatosis and Haemosiderosis). A raised percentage transferrin saturation in isolation may be the earliest indicator of iron overload.

Serum ferritin concentrations typically fall in the last 4 weeks of normal pregnancy. This reflects transfer of organic iron from mother to fetus, rather than any change in iron metabolism. However, a ferritin concentration <30 µg/L is still considered diagnostic of iron deficiency at any stage of pregnancy. As for non-pregnant individuals, ferritin concentrations in the 30-100 µg/L range could indicate iron deficiency in the presence of co-existing inflammatory disease.

Isolated reduction of serum iron is of dubious significance given the wide variability of serum iron concentrations.

See Table 3.
Reference:

Brugnara C. Iron deficiency and erythropoiesis: new diagnostic approaches. Clin Chem 2003; 49: 1573-8. Review.

Royal College of Pathologists of Australasia. Iron Studies Standardised Reporting Protocol. Surry Hills: RCPA, 2013.