The complete blood count (NFS) or complete blood count is a frequently prescribed blood test which consists of analyzing red and white blood cells and platelets. When to do it? What standards?
An NFS assessment (or hemogram) is a biological examination allowing the different figurative elements of the blood to be counted (platelets, red blood cells, different categories of white blood cells). It is one of the most common biological examinations. It allows to check the general state of health of a person and to detect anemia, presence of infection or blood disease. It is particularly indicated in certain situations such as pregnancy, in occupational medicine, during a check-up before an operation and in the follow-up of certain treatments.
What is the definition of CBC (hemogram)?
“NFS (blood count) or lhemogram is a blood test that allows you to look quantitatively and qualitatively at blood cells“, sums up Dr. Clémence Mediavilla, hematologist at Saint-Antoine Hospital. By analyzing the blood collected, we can observe the appearance of blood cells and their number. A too high or too low number of cells, or an abnormal aspect, makes it possible to direct the diagnosis. Depending on the parameters analyzed using the blood count, doctors can request additional tests to detect a possible disease.
Why do an NFS scan?
The examination is done through a blood test. “It is routinely prescribed by the attending physician, the gynecologist… The anesthetist can also prescribe it before surgery. Otherwise, it occurs in the context of a particular search for pathology“, adds the specialist. The doctor can prescribe a blood count in case of unusual tiredness or abnormal shortness of breathI. “So, we will rather look for anemia“, specifies Dr. Mediavilla. He can also ask for it in the event of heavy bleeding. “We will rather look on the platelets side“.
Do you have to be fasting to do an NFS check-up?
The examination does not require fasting.
What are normal CBC values?
Different parameters are evaluated during a blood count.
► hemoglobin is a protein found in red blood cells. Normal values are between 12 and 16 g/dL in women, and 13 and 16.5 g/dL in men. If the hemoglobin is abnormal, the MCV (mean corpuscular volume: size of the red blood cells) is analyzed, the levels of which should be between 80 and 100 fl. We can also analyze reticulocytes (immature red blood cells produced by the bone marrow), whose normal values are between 20 and 120g/L. “But you should know that some values, even abnormal, may have no consequence: the normality of this rate depends on the situation“, specifies Dr. Mediavilla.
► Platelets are elements circulating in the blood and allowing its coagulation. Normal values are between 150,000 and 400,000/mm3.
► Leukocytes are the white blood cells. The normal value should be between 4000 and 10,000/mm3. In case of abnormal levels, the leukocyte subtypes are analyzed in order to guide the diagnosis. Among them: neutrophils (normal values: between 1500 and 7000/mm3), and lymphocytes (between 1500 and 4000/mm3).
What does abnormal NFS mean?
► Low hemoglobin. “A low hemoglobin associated with a low MCV and high reticulocytes can indicate an iron deficiency. An additional test is then prescribed: the iron assay. A low hemoglobin associated with low reticulocytes and a high MCV rather suggests a vitamin deficiency B9 and B12, or kidney or thyroid damage”.
► Elevated hemoglobin. On the contrary, when hemoglobin levels are higher than normal values, it is called polycythemia. This can reveal polycythemia vera (although the incidence is low), or hypoxemia (abnormal decrease in the amount of oxygen in the blood). “The body increases the production of red blood cells to oxygenate the blood. The same phenomenon is found in people who go to altitude, where oxygen is rarer.“. Elevated hemoglobin can also suggest a tumor in the liver, kidney or cerebellum, but cases are rare.
► Lower pads. A low level of platelets can be associated with a hematological disease that destroys blood platelets, such as idiopathic thrombocytopenic purpura, or DIC (disseminated intravascular coagulation). “We can observe in rare cases a decrease in platelets in patients in intensive care who present with septic shock”, adds Clémence Mediavilla. “If there is a problem with the production of platelets, we will prescribe an additional examination: the myelogram (examination of the bone marrow)”. We will then look for a possible chronic myeloid leukemia or myelodysplasia.
► Platelets high. High platelets can be linked to iron deficiency, infection, a removed or non-functioning spleen, or even a hematological disease, such as essential thrombocythemia.
► Low leukocytes. In case of low leukocytes, a myelogram is necessary. “This may be related to a deficiency, or an autoimmune disease, or even myelodysplasia.“.
► High leukocytes. A high neutrophil count can indicate inflammation, infection, or in rarer cases, chronic myeloid leukemia. “A high lymphocyte count in a child or adolescent may suggest the presence of a virus. In adults, the lymphocytes will then be checked again; if their rate remains high, we will look for chronic lymphocytic leukemia, or lymphoma“.
When to worry?
“Often, patients tend to be alarmed when they present levels lower or higher than the reference values. However, you should know that in most cases, this is of no consequence..”
Thanks to Dr Clémence Mediavilla, hematologist at Saint-Antoine Hospital (AP-HP).