Generality
Hemosiderin is an iron-depositing protein that can be dosed by taking small tissue samples (biopsy).
Hemosiderin alterations assume a predictive value for the diagnosis of various pathologies, including: chronic infections, stable or old heart disease, iron deficiency anemia and liver cirrhosis.
Abnormal accumulations of hemosiderin occur also in the case of disorders of iron metabolism, with excessive deposition of this metal in the tissues (as in hemosiderosis and hemochromatosis).
This parameter is not dosed in the blood, but can be highlighted in various tissues, using special histochemical reactions and an optical microscope. Rather than assessing the magnitude of the body's iron reserves, this analysis serves to highlight pathological sideroblasts (expression of metal accumulation in erythroblasts).
What's this
Hemosiderin is a protein that binds iron. Together with ferritin, this protein has the important function of storing iron in the body.
From the structural point of view, hemosiderin is composed of the aggregation of ferritin molecules with other elements (lipids, sialic acid, proteins and porphyrins).
Excessive local or systemic iron induces hemosiderin to accumulate in cells.
Storage iron: hemosiderin and ferritin
The total amount of iron contained in the organism is around 3-5 grams, divided between the circulating part (hemoglobin - about 2.5 g; myoglobin and enzymes) and body deposits, represented by ferritin and hemosiderin.
Ferritin is present in the blood, while hemosiderin is mainly located inside the cells responsible for the synthesis of red blood cells. Among these two storage proteins, ferritin is the only parameter that can be evaluated in the blood, to quantify the amount of iron in the body.
Biological role and clinical significance
Hemosiderin is a heterogeneous organic compound, consisting essentially of a protein shell that contains iron salts; we are indeed talking about one of the two forms of storing the mineral in the body.
The storage compartment accounts for 20-30% of body iron; this mineral, however, is not stored as such, but bound to specific proteins.
Thus two distinct forms of storage are recognized, called ferritin and hemosiderin. The latter derives from the first, given that approximately one third of the circulating ferritin is complex in more stable and insoluble aggregates. Hemosiderin - contained in this sort of granules filled with semi-digested ferritin molecules - is found mainly in the cells of the monocyte-macrophage system of the bone marrow and spleen, and in the liver cells of Kupffer. Ferritin, on the other hand, is virtually contained in all body cells (mainly in hepatocytes) and in tissue fluids (for example in plasma in minimal concentrations).
Compared to that enclosed in ferritin, the deposition iron contained in hemosiderin is more difficult to metabolize; in case of need it is therefore slowly available. In addition, hemosiderin contains more iron and less protein than ferritin, and is not soluble in water.
Given the above, it is not surprising that the iron body concentration conditions the distribution between ferritin and hemosiderin; in particular, at low deposition levels, iron is mainly stored as ferritin, while as the element increases the hemosiderin proportion increases proportionately.
Why do you measure
Hemosiderin is not dosed in the circulation, but is observed under an optical microscope in the form of granules that can be colored in blue with potassium ferrocyanide (Perls staining). The samples to be examined are represented by tissues or smears of marrow blood (or myeloaspirato) .
Hemosiderin increases especially in states of iron overload, resulting from a degradation process of ferritin or other mechanisms that occur when the system that regulates the synthesis of ferritin is saturated.
Note
Most iron reserves are present in the form of Ferritin . If the storage capacity of this protein is exceeded, a noticeable proportion of Hemosiderin appears . In other words, when there is an excess of iron at the local or systemic level, ferritin forms hemosiderin granules, which can be easily observed under an optical microscope .
Hemosiderin tends to accumulate in the liver, if access to the metabolic pathway that allows the correct disposal of iron is lost. The result is an increase in hemosiderin found at the level of the parenchymatous organs (liver, heart, pancreas, endocrine glands etc.).
Hemosiderin assumes some relevance in the diagnosis of various diseases. An increase in tissue iron uptake or elevated serum metal levels may occur due to congenital defects or different causes, particularly affecting the liver and pancreas.
Specifically, the increase of this parameter is highlighted as a result of: infectious processes, liver cirrhosis, uremia, repeated blood transfusions and different forms of anemias, including pernicious ones.
Normal values
Under normal conditions, small amounts of hemosiderin can be observed in bone marrow, spleen and liver macrophages, where they are engaged in the hemocateresis of red blood cells.
High Hemosiderin - Causes
Excessive intake of iron through drugs, foods, supplements or transfusions may be responsible for overloads, which are referred to as hemosiderosis or secondary hemochromatosis.
Important deposits of hemosiderin are also formed in the organs affected by bleeding, heart attacks or traumas, as well as in metabolic disorders with excessive accumulation of iron in the tissues (hemochromatosis).
Low Hemosiderin - Causes
The deficiency or absence of haemosiderin in the bone marrow is the first sign of an iron deficiency in the body, as is the case in sideropenic anemias of a certain severity.
The presence of hemosiderin in the urine, on the other hand, is a sign of intravascular hemolysis.
How to measure it
Hemosiderin is not dosed in the circulation, but is observed in the tissues or medullary smears (or myeloaspirates), in the form of yellow-brownish granules in the non-colored preparations and green-blue after the histological staining of Perls (also called coloring Prussian Blue).
Preparation
Hemosiderin is identified histologically, so no special precautions need to be taken before analysis. Sometimes, it is necessary to observe a fasting period of at least 8 hours.
The drugs do not affect the outcome of these tests, except if you are following an iron-based therapy; therefore, it is always advisable for the doctor to be aware of it.
Interpretation of Results
- Low levels of hemosiderin indicate the absence of iron in the deposits. In sideropenic anemias, the decreased concentration of the protein is considered an important early marker, being able to anticipate the appearance of symptoms even by a few months.
- High levels of hemosiderin indicate the possible existence of iron overload. This condition may depend on a greater absorption of ingested iron through food, due to a congenital defect (hemochromatosis); hemolytic anemias (premature lysis of red blood cells causes the release of enormous amounts of iron) and repeated blood transfusions. Larger amounts of hemosiderin appear in the tissues of chronic blood stasis (eg lung) or that have been affected by bleeding, heart attacks and traumas.
