Blood count

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Automated determination of a small blood count

In medicine, the blood count ( hemogram ) is a standardized compilation of important findings from a blood sample . It gives an overview of the cellular components contained in the blood . It contains data on both the quantity of cellular blood components and their morphology (external shape).

A distinction is made between the small and large blood counts .

Blood count examinations are generally carried out using EDTA blood.


The cellular blood components are red blood cells ( erythrocytes ), white blood cells ( leukocytes ) and thrombocytes (blood platelets, older term after Schilling ). Normally, about 43 to 50% (men) or 37 to 45% (women) of human blood consists of blood cells. The proportion of the cellular components in the total volume of the sample is known as the hematocrit . The blood fluid that remains after cellular components have been separated off (e.g. by centrifugation) is the blood plasma , which contains electrolytes , coagulation factors and other plasma proteins . If the blood is left to stand for a while, a coagulation reaction sets in, the coagulation factors are activated and together with the cellular components (especially the thrombocytes) form a clot ( thrombus ). The supernatant consists of plasma without coagulation factors and is then called blood serum .

"Small" blood count

The following information provides reference values ​​for adults. Reference values ​​for children, especially for infants , sometimes differ significantly from this.

value woman man unit Explanation
4-10 Thousand / µl White blood cells are part of the immune system . Increased in inflammation , allergy , gout attack. Extremely increased in leukemia . Reduced in the case of virus infections (measles, flu), poisoning.
(RBC or ERY)
4.3-5.2 4.8-5.9 Million / µl Red blood cells (erythrocytes) carry oxygen to organs. Increased when there is a lack of oxygen, stress, dehydration. Decreased in cases of anemia or blood loss. Anemia can result from a lack of iron ( iron deficiency anemia ). Reference range is higher in thalassemia .
(HGB or HB)
12-16 13.5-17.5 g / dl The red blood pigment binds oxygen. Value changes with the number of red blood cells.
(HCT or HKT)
37-47 40-54 % Volume fraction of red blood cells in total blood. Increases with proliferation of erythrocytes, fluid loss, in smokers. Reduced in the case of anemia, pregnancy .
MCV 78-94 fl Average volume of an erythrocyte. Used to differentiate anemia. (MCV = hematocrit / erythrocyte count).
MCH (Hb E ) 28-34 pg Average amount of hemoglobin per red cell. This parameter is also used to differentiate between anemia. (MCH = hemoglobin / erythrocyte count).
Mean Corpuscular Hemoglobin Concentration (MCHC) 30-36 g / dl Share of hemoglobin in the total volume of red blood cells (= hematocrit). (MCHC = hemoglobin / hematocrit, MCHC = MCH / MCV).
150-400 Thousand / µl The thrombocytes (blood platelets) are an important factor in blood clotting .
possibly reticulocytes 7-15 Erythrocyte precursor cells. Normally only a few reticulocytes should be detectable in the blood. An increase speaks for an increased formation of new blood (e.g. after a major blood loss).
if necessary, mean platelet volume
(MPV or MTV)
7-12 fl Used to differentiate between disorders of platelet shape / number
if necessary, erythrocyte distribution
width (RDW)
11.9-14.5 % Elevated values ​​are an indication of the presence of various forms of anemia.

"Complete blood count

In addition to the small blood count, which only contains the total leukocyte count, the complete blood count also includes the differential blood count . This is an exact breakdown of the subgroups of the leukocytes (white blood cells). This differential blood count can be machine or manual, i.e. H. can be created microscopically . The percentage of the individual blood cell types is determined by counting a blood smear microscopically or with the help of automated counting devices such as the Coulter counter . The microscopic count is more complex and quantitatively less precise, but is often essential for a final qualitative assessment. Pathogenic cell forms such as atypical lymphocytes (virocytes) can often not be correctly assigned by machine and diagnostically relevant information is lost. The shape of the red blood cells ( erythrocytes ) is assessed with a blood smear.

Blood disorders

A wide variety of health conditions can lead to abnormal blood counts.

Quantitative changes

Deviations in the number of reticulocytes

Even if the percentage of reticulocytes is not normally determined in the routine, it is an important measure for the formation of new erythrocytes in the bone marrow. The value measured here allows a distinction to be made as to whether it is a metabolic disorder in which the reticulocyte proportion is increased or a formation disorder in which the reticulocyte proportion is normal or decreased.

Disorders of the red blood cells

Appearance in the blood smear and its meaning or occurrence:

  • Macrocyte : diameter> 10 μm, increased volume, but normal shape; in alcoholism
  • Megalocyte: enlarged, hyperchromic (more strongly colored), oval erythrocyte; with vitamin B 12 deficiency, folic acid deficiency , iron deficiency, thalassemia
  • Microcyte : diameter <7 μm, reduced volume, but normal shape; with iron deficiency, thalassemia
  • Poikilocyte: abnormally shaped erythrocyte (coat-, club-, pear-shaped); in severe anemia
  • Reticulocyte : young, anucleated erythrocyte with reticular nuclear remnants; up to 1.5% normal, increased with increased erythrocyte formation (e.g. haemolysis)
  • Schistocyte (also fragmentocyte): torn erythrocyte; with HUS (hemolytic uremic syndrome, mechanical hemolysis (e.g. artificial heart valve))
  • Sickle cell: short-lived erythrocyte (<42 days) that takes on a sickle shape when deprived of oxygen; Sickle cell anemia
  • Spherocyte : spherical cell; with spheroidal cell anemia
  • Echinocyte (thorn apple cell): deformed, round erythrocytes with thorn-like cell extensions
  • Target cell ( target cell ): erythrocyte with abnormal color distribution ( hemoglobin in the center and ring-shaped at the edge); in thalassemia, hemolytic anemia, severe iron deficiency anemia
  • Anisocytosis : “no cell is the same size as another”; in all anemia
  • Anulocyte: ring-shaped erythrocytes with low hemoglobin content and the resulting pale color; in iron deficiency anemia
  • Basophilic stippling: basophilic substance distributed in dots (dark stippling) in the erythrocytes and increased erythropoiesis; for lead poisoning and thalassemia
  • Dacrocyte: teardrop shape; in osteomyelosclerosis
  • Elliptocyte: oval erythrocyte; with rare congenital elliptocytosis
  • Heinz inner corpuscles : degenerated, intracellular hemoglobin, which is only visible after special coloring; in toxic, hemolytic anemia, methemoglobinemia, G6P-DH deficiency
  • Howell-Jolly corpuscles : nuclear residues in the erythrocytes; after removal of the spleen.
  • Cabot ring : remains of the spindle apparatus
  • Anemia ( anemia ) - a decrease in the level of hemoglobin in the blood due to insufficient red blood cells and / or a decrease in MCHC
  • Polyglobulia (fullness of blood) - too many red blood cells
  • Polycythemia vera (abnormal cell proliferation in the blood) - too many erythrocytes
  • Pycnocyte : shrunken erythrocyte, mainly due to oxidative stress

Leukocyte disorders

Platelet disorders

Qualitative changes

Disorders of the red blood cells

  • Anisocytosis : red blood cells of different sizes
  • Storage: abnormal storage, such as " roll formation "
  • Microcytosis : too small erythrocytes
  • Macrocytosis : red blood cells that are too large
  • Poikilocytosis : differently shaped red blood cells
  • Polychromasia : ability to stain pathologically changed or immature erythrocytes with acidic and basic dyes (usual Pappenheim staining = May-Grünwald + Giemsa staining)
  • Thalassemia and other genetic defects affecting red blood cells: lead to deformed / smaller / larger red blood cells.
  • Cell inclusions: inclusions such as Cabot rings or basophilic stippling

Platelet disorders

  • Thrombanisocytosis - different sized platelets (= increased distribution range of the platelet volume)


Web links

Wiktionary: blood count  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Normal values ​​in the small blood count.; Retrieved August 2, 2013.
  2. Normal blood counts in children.; Retrieved August 2, 2013.
  3. reticulocytes.; Retrieved August 2, 2013.
  4. Lea Schnurbus: disorders of the blood picture . 2013