Do you know how to interpret the results of a complete blood count

The hemogram is one of the laboratory tests most commonly used by physicians to study any patient. In the Community of Madrid alone, almost three million blood counts are performed every year. The objective of this study is to evaluate the cellular components of the blood (red blood cells or erythrocytes, white blood cells or leukocytes and platelets) and a series of parameters related to them.

Alterations in the normal values of the hemogram occur both in diseases of the blood and in diseases of other organs. A very important number of diseases are going to have expression in the blood count so it is considered an essential test in the medical evaluation of a person.

How the blood count test is performed

This test is performed with a laboratory apparatus called an “automatic hematological counter”. This is a very standardized study of which all laboratories will give us the same parameters when requesting a hemogram. If we have a general analysis for a medical problem or for a check-up, when we pick them up we will probably have the hemogram on the first page.

When we start reading it, we find a series of acronyms or abbreviations that we are often unable to interpret. If, in addition, we find some values in “bold” or with an arrow pointing up or a date pointing down, a certain uneasiness may set in. Dr. Google can then either calm us down or lead us to total confusion. For everyone’s peace of mind, most of the alterations seen in a hemogram are usually not relevant.

From a practical point of view, the blood count can be divided into three parts; those related to red blood cells and their oxygen transport function, those related to the number of white blood cells and finally those related to platelets.

Parameters related to red blood cells

The most important parameter for assessing red blood cells and their function is hemoglobin. Sometimes we are concerned about hematocrit or the number of red blood cells, but these values have more variability. It should be remembered that normal hemoglobin values vary with age and sex; a 20-year-old male is not the same as a young child or a 90-year-old woman.

If hemoglobin is normal for our sex and age, even if there are alterations in the rest of the parameters related to red blood cells, it is rare that there will be a relevant health problem. When hemoglobin is low we have anemia. If the hemoglobin is high we have polyglobulia or polycythemia. The causes of anemia are multiple, with bleeding and iron deficiency being the most frequent. As for the causes of increased hemoglobin, the most frequent are smoking and respiratory problems, including sleep apnea.

The hematocrit corresponds to the percentage of red blood cells in a whole blood sample. It is related to the number of red blood cells and hemoglobin; by itself it has a less relevant value than hemoglobin.

The number of red blood cells or erythrocytes is also of less value than hemoglobin and is usually related to hemoglobin. Generally the hematocrit and red cell count help us physicians to observe whether there is congruence in the results and to guide the diagnosis in case of anemia or polyglobulia.

The other parameters are called erythrocyte indices:

  • Mean Corpuscular Volume (MCV): This refers to the size of the red blood cells which, if anemia is present and altered, helps physicians to know the cause. Small red blood cell size (MCV ↓) is often related to iron deficiency and chronic bleeding. Large RBC size is usually relevant if the RBC size is significant and is primarily related to vitamin B12 or folic acid deficiency.
  • Mean corpuscular hemoglobin (MCH): the average amount of hemoglobin in a red blood cell. A low MCH indicates a decrease in hemoglobin content per red blood cell.
  • Mean corpuscular hemoglobin concentration (MCHC) is the amount of hemoglobin relative to the size of each red blood cell. If elevated it usually indicates the presence of small red cells loaded with hemoglobin and vice versa.
  • ADE or IDE; it is the erythrocyte dispersion index or the amplitude of the erythrocyte distribution curve. It is a way of measuring the “uniformity” of red cells. A high number means that there is no uniformity and we will find both very small and very large red cells. It is typical of iron or vitamin deficiencies.
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Erythrocyte indices are results given by hematological counters and are usually meaningless if hemoglobin and the other main parameters are normal. If anemia is present, they will help us to determine the cause of the anemia.

Parameters related to white blood cells

In the hemogram the white blood cells are called leukocytes and the result offered is: on the one hand, their total number, and on the other hand, the number of each of their subtypes (in percentage or absolute number).

The number of leukocytes is very variable. They are affected by many processes, most of them banal. Only extremely low or high numbers of leukocytes, which appear unexpectedly, are associated with relevant health problems.

The most relevant type of leukocytes are neutrophils, which defend us against infections. Low numbers are seen in many situations and are usually not particularly relevant, especially if the patient is asymptomatic and there is no apparent cause. Numbers below 1000 may require additional studies. Slightly high numbers are seen in many situations, including habitual smokers.

Lymphocytes are the second most abundant type of leukocytes. They are responsible for the most specific and selective immunity. They also have a great variability and only very increased or very decreased numbers that appear unexpectedly may be relevant.

Monocytes are the first-line phagocytic cells of our defense system against infection. Their number also has a great variability and only very striking numbers appearing unexpectedly may indicate any significant disease.

Eosinophils are a type of leukocyte that is altered with some frequency in patients with allergy, asthma and parasitic infections. Their elevation may be a marker of these. Low eosinophil numbers alone are rarely going to be significant.

Basophils are a generally irrelevant type of leukocyte, being a common marker of a type of blood disease called myeloproliferative syndromes.

Platelet-related parameters

The number of platelets is a fundamental parameter of the hemogram, the other platelet indices being of little value. Small alterations of the platelet count are very frequent and usually do not indicate relevant problems. Clearly decreased platelet counts below 100,000 per microliter or clearly increased (more than 400,000), without apparent cause, usually require investigation.

Hematological counters automatically give us a series of secondary parameters called platelet indices that have no value if the platelet count is normal. The mean platelet volume, if increased in a patient with low platelets, usually indicates larger than normal young platelets and supports that the cause is an excess consumption of platelets. The platelet cytometer or platelet distribution curve is of very limited usefulness in counseling a patient with a low platelet count.