Dr Zimmermann, what importance do you personally place on the reticulocyte haemoglobin equivalent?

RET-H_e is, in my view, a very good biomarker for the iron supply in erythropoiesis. It has taken on great importance in the diagnosis of iron metabolism and has become an established routine parameter. It gives clinicians a very good overview as to whether the patient currently has the early stages of an iron deficiency or not. This parameter is also highly standardised and can be measured round the clock very quickly and cost-effectively. This makes it a frequently requested parameter, especially in internal medicine wards, gynaecology and paediatrics, but also surgical wards that want to check before surgery if the patient has anaemia. You simply want to see if the bone marrow is currently working well in terms of erythropoiesis.

Delta-H_e is another parameter that is not as well-known as RET-H_e. What does this parameter tell you?

Delta-H_e is a new, cell-based biomarker that is established by measuring reticulocytes on the XN-Series. You have to go into a little more detail to explain its use: when bacteria enter our body and trigger inflammation, there are processes that have been going on for millions of years that are basically similar in all living creatures. There is a rise in certain cytokines, i.e. messenger substances of the immune system, such as interleukin-6. This first non-specific alarm signal then triggers various reactions resulting in an increase in hepcidin, an acute phase protein. The hepcidin ensures that transmembrane iron-export proteins are internalised from the cell surface.

This means that the iron is locked away in the cells and does not enter the blood stream again until the hepcidin falls. This is a protective mechanism of the body to withdraw iron that invading bacteria need for their growth. However, this also means that there is not enough iron for erythropoiesis. As a result, the haemoglobin content in the reticulocytes is lower and the Delta-H_e value turns to negative because the haemoglobin concentrations in the mature red blood cells exceed those of the young reticulocytes. Normally, it is the other way around. Once the infection has been fought off, hepcidin expression falls and the iron transporters return to the cell surface so that iron can be absorbed and is then also available for erythropoiesis – the reticulocyte filled with more haemoglobin (iron) becomes larger than the mature red blood cell and the Delta-H_e returns to positive.

And what is the importance of the Delta-H_e value in these circumstances?

Delta-H_e is the difference between the haemoglobin content of the newly-formed reticulocytes (RET-H_e) and the haemoglobin content of the mature red blood cells (RBC-H_e). The Delta-H_e value that is usually positive in healthy people, between + 2 pg and + 8 pg, turns negative within a few hours because there is an iron deficiency due to inflammation. If the Delta-H_e value suddenly switches to negative, you can suspect that the patient most likely has an acute phase reaction or maybe has developed sepsis. In the case of sepsis, the Delta-H_e can promptly switch to - 4 pg, - 6 pg or - 8 pg. With successful treatment, if the patient responds to the drugs and the infection (or inflammation) is blocked, the Delta-H_e can quickly tell you if the bone marrow is getting enough iron and it switches back to positive. In the case of iron deficiency anaemia, you would not expect the Delta-H_e value to be negative. As long as the inflammatory component is missing, the relationship between the haemoglobin concentrations of reticulocyte to red blood cell is not pathologically regulated and so the value is still positive. It is only when there is inflammation that the value becomes negative.

Does that mean that Delta-H_e could also play a role in monitoring?

Definitely. And you could easily combine the parameters Delta-H_e and RET-H_e in a diagnostic plot with RET-H_e on the y-axis and Delta-H_e on the x-axis. We divide this into nine fields and then you can see if the patient has an inflammatory disease, iron deficiency or thalassaemia, similar to the so-called ‘Thomas plot’.

How do you use the Delta-H_e in laboratory routine?

Our colleagues working in a clinical setting use RET-H_e as an established routine parameter. We still have to inform our colleagues about Delta-H_e with lectures or handouts. But I think it can become a very good addition or even a replacement for the classic acute phase parameters such as CRP (C-reactive protein) or PCT (procalcitonin) when sepsis is suspected if it is used in combination with other markers. We and other groups conducted studies where a range of the new cell-based haematological markers are combined with each other. We found that with Delta-H_e and other parameters, a systematic bacterial infection can be detected very early on as these parameters respond faster than CRP and PCT. In the future, this could provide a diagnostic benefit and the ability to see if the treatment is working or not.

Summary

• Delta-H_e is the difference between the haemoglobin content of newly-developed reticulocytes (RET-H_e) and mature red blood cells (RBC-H_e).

• In combination with other parameters, the Delta-H_e parameter can accelerate the diagnosis of systemic bacterial infections.

Photo source: Lene Münch