What is hemoglobin?
Hemoglobin is an important component of red blood cells, erythrocytes. It binds oxygen (O2) and carbon dioxide (CO2), enabling their transport in the blood. It is formed in the precursor cells of the erythrocytes (proerythroblasts, erythroblasts), degraded mainly in the spleen. On laboratory reports, hemoglobin is usually abbreviated to “Hb” and expressed in grams per liter or grams per deciliter (g/L or g/dL).
Hemoglobin: structure and function
Hemoglobin is a protein complex consisting of the pigment heme and the protein moiety globin. It has four subunits, each of which has a heme molecule. Each of these heme molecules is capable of binding an oxygen molecule, so that a hemoglobin complex can carry a total of four oxygen molecules.
The hemoglobin takes up the oxygen from the air we breathe in the small pulmonary vessels, transports it throughout the body via the bloodstream and delivers it to the cells in the tissues. Hemoglobin loaded with oxygen is called oxyhemoglobin; when it has released all O2 molecules, it is called deoxyhemoglobin. In its unloaded form, it can absorb carbon dioxide in the body, which it then carries back to the small lung vessels. There, the CO2 is released and exhaled.
Fetal hemoglobin
HbA1c
HbA can be divided into different subtypes, one of which is HbA1c. It plays an important role in the therapy control of diabetes. You can read more about this in the article HbA1c.
When do you determine hemoglobin?
Hemoglobin concentration is a standard part of every blood test. The Hb blood value is of particular interest if anemia or an increase in red blood cells (polyglobulia) is suspected. The Hb value in the blood also provides indirect information about disturbances of the water balance (dehydration, hyperhydration).
If certain diseases are suspected, and as part of some preventive examinations, the doctor can also use special test procedures to check whether hemoglobin is present in the urine or stool. For example, Hb in urine above a certain concentration provides evidence of, among other things:
- Decay of the red blood cells in the blood (hemolysis)
- Kidney diseases (carcinoma, renal tuberculosis and others)
- bleeding in the urinary tract
When is the hemoglobin level normal?
When is the hemoglobin value decreased?
Decreased laboratory values (Hb of less than 14 g/dl in men or less than 12 g/dl in women) indicate anemia. However, this alone does not indicate the cause of the anemia: For this, other red blood cell parameters must be determined, for example, erythrocyte count, hematocrit, MCV and MCH. Examples of diseases with anemia are:
- Iron deficiency anemia (common in young women)
- Synthesis disorders of globin chains (thalassemias, sickle cell disease).
- Chronic diseases (for example, cancer, chronic inflammation or infectious diseases)
- Folic acid deficiency or vitamin B12 deficiency
Decreased hemoglobin also occurs with acute bleeding because the body is unable to make new red blood cells quickly enough.
Overhydration (hyperhydration) also leads to a lowered Hb value in the laboratory findings. However, this is only a relative deficiency. The Hb content in the body remains the same overall, but the blood volume increases, causing the Hb concentration to decrease. This is a dilution anemia, so to speak. Overhydration occurs, for example, when infusion solutions are supplied rapidly or in the context of kidney failure.
Further information: Hemoglobin too low
When is hemoglobin elevated?
An elevated hemoglobin value is often an indication of an increased number of red blood cells. In medicine, this is called polyglobulia. It occurs in the following situations, among others:
- polycythaemia vera (pathological multiplication of various blood cells)
- Chronic oxygen deficiency (heart or lung diseases as well as prolonged stay at high altitudes)
- autonomous or external supply of EPO (in the context of kidney diseases or doping)
The Hb value can also be too high if there is a lack of fluid in the body (dehydration). In this case, analogous to dilution anemia, it is merely a relative excess of red blood cells, which is compensated for by the supply of fluid.
What to do if the hemoglobin value changes?
Slight deviation from the standard Hb value is usually harmless. However, altered hemoglobin values also occur in the context of various diseases that require further clarification.
If a high hemoglobin value provides evidence of polyglobulia and this is confirmed, there is an increased risk of vascular occlusion due to the more viscous blood. Polyglobulia is then treated with phlebotomies, and the physician continues to check the hemoglobin regularly.
