RET-He parameters for functional iron deficiency diagnostics

Determining of the haemoglobin content of the reticulocytes = RET He (reticulocyte haemoglobin equivalent) constitutes a cost-effective parameter that is available for diagnostics and monitoring of iron deficiency diseases.

Due to the approx. 120-day life time of erythrocytes in peripheral blood, iron deficits in erythropoiesis with the classic haematological parameters such as Hb, MCV and MCH – along with hypochromic erythrocytes – can only be detected much later. In contrast, reticulocytes, which come directly from bone marrow and only need about two days to reach maturity in peripheral blood, reflect the current iron supply for erythropoiesis in the bone marrow.

Conventional biochemical markers for determining iron metabolism, such as serum iron, transferrin and ferritin, are in part so severely impacted in the course of an acute phase reaction that any clinical correlation of these results is difficult. The measurement of the haemoglobin content in still immature red blood cells, the reticulocytes, is not affected by an acute phase response, however.

The current quality of erythropoiesis can thus be detected promptly, thereby providing an important aid in the diagnosis and monitoring of iron deficiency diseases.

The indications for determining RET-He are:


  • Determining functional iron deficiency in the chronic disease forms of anaemia, such as in inflammation, infections and malignant tumours
  • Diagnosing latent iron deficiency (incipient hypochromic)


  • Monitoring erythropoietin and/or iron therapy, especially in renal anaemia, if necessary in combination with ferritin and a soluble transferrin receptor (sTfR), see „Thomas plot”

Normal therapeutic range
> 28 pg

Test material

  • EDTA blood, as with the blood count for RET He
  • Serum for ferritin and a soluble transferrin receptor

The „Thomas plot”

Diagnostic options


Functional iron concentration



Diagnosis: Normal iron supply

Therapy: Erythropoietin
Anaemia patients in Quadrant 1 should primarily be given EPO therapy.


Diagnosis: Latent iron deficiency
Diagnostics: Anaemia patients in Quadrant 2 have latent iron deficiency (empty stores, but an only barely adequate supply of iron in the bone marrow).

Therapy: Iron
Patients in Quadrant 2 should primarily be given oral iron therapy.


Diagnosis: Functional iron deficiency with full iron stores
Diagnostics: Patients in Quadrant 4 exhibit functional iron deficiency with full iron stores.

Therapy: Iron (i.v.) + erythropoietin
Patients in Quadrant 4 should be given EPO therapy in combination with iron substitution (i.v.).


Diagnosis: Lack of iron stores and functional iron deficiency
Diagnostics: Patients in Quadrant 3 exhibit both a lack of iron storage and functional iron deficiency (an inadequate iron supply with empty iron stores).

Therapy: Iron
Patients in Quadrant 3 should primarily be given oral iron therapy.

                           ⇐ Iron store concentration
                                       STfR / log ferritin


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