September 14, 2023 Author : Ana Sofia Corredoura The blood count, or complete blood count or CBC, is a test that evaluates the number and morphology of blood cells , which are: Red blood cells or erythrocytes, which contain hemoglobin and are responsible for transporting oxygen; White blood cells or leukocytes, which play an important role in fighting infections; Platelets or thrombocytes, which are involved in blood clotting, helping to control bleeding. This CBC is carried out on a blood sample , most often drawn from a vein in the arm on the anterior face of the elbow. No preparation is required to perform a CBC. However, in most cases, when blood tests are requested, other parameters are included in addition to it, some of which require fasting. Therefore, it is usually said that to carry out blood tests a fasting period is necessary. When can a complete blood count be requested? The CBC is one of the main blood tests that is requested and is useful in multiple situations, including: In regular health surveillance, which is why it is part of routine blood tests; Help with diagnosis when there is a suspicion of a disease or a need to clarify the cause of some symptoms; Regular monitoring of already diagnosed diseases that affect blood cells; Monitoring the results of treatments that affect blood cells. Complete blood count results may show an increase or decrease in various blood cells and changes in hemoglobin values, identifying a problem or indicating a need of additional tests to clarify if there is any problem. Many blood tests, such as CBC, can be performed with different instruments, equipment and methodologies. Therefore, it is good practice to use the same laboratory, whenever possible , to monitor the hematological parameters of the same person. CBC results The blood count results are presented with several parameters related to: Red blood cells or red series, also called erythrogram: White blood cells or white series, also called leukogram; Platelets. Erythrogram Erythrocytes : is the number of these cells per unit volume of blood, generally per liter (L) or per milliliter (mL). Hemoglobin : is the concentration of this protein that is responsible for the color of the blood and which transports oxygen. It is presented in units of weight (or mass) per unit of blood volume, usually in grams per deciliter (g/dL). Hematocrit : is the proportion of the blood volume occupied by red blood cells. It is presented as a percentage (%). Mean corpuscular volume (MCV): is the average size or volume of red blood cells. It can be calculated by dividing the hematocrit value by the number of red blood cells (displayed in fentoliters - fL). Mean corpuscular hemoglobin (MCH): is the average amount of hemoglobin that exists in red blood cells (presented in picograms - pg). Mean corpuscular hemoglobin concentration (MCHC): is the hemoglobin concentration in red blood cells. Red cell distribution width (RDW): is a measure of the variation in the size of red blood cells and is presented as a percentage (%). Conditions such as pregnancy, age, sex, intense physical exercise, altitude, medications, or smoking can affect the values for some of these parameters. Leukogram Leukocytes : is the number of these cells per unit of blood volume, usually per liter (L) or per milliliter (mL). In addition to the total number of white blood cells, the leukocyte count includes the determination of the number of each of the 5 types of these cells – neutrophils, eosinophils, basophils, lymphocytes and monocytes – presented in relation to the volume of blood, generally per liter (L) or per milliliter (mL) and also in percentage (%) of total leukocytes. The ratio between the various types of white blood cells differs throughout life. During childhood lymphocytes are predominant, while in adulthood neutrophils have higher absolute values. The total number of white blood cells can also vary from person to person or throughout the day. Factors such as the menstrual cycle, rest, exercise or strong emotions can slightly alter white blood cell values. Platelets Platelets : is the number of these cells per unit of blood volume, usually per liter (L) or per milliliter (mL). Mean platelet volume (MPV): is the mean size or volume of platelets. It is presented in femtoliters (fL). Platelet count : is the proportion of blood volume occupied by platelets. It is presented as a percentage (%). Platelet Distribution Width (PDW): is the measure of platelet size variation and is presented in percentage (%) Results interpretation The results of any medical test should always be interpreted by a healthcare professional in the context of each person situation and considering other data available, such as personal and family health history, present complaints, physical examination results, and other medical test results. Although CBC reports usually include reference values for each of the parameters, remember that : Small variations may be normal, and your doctor is the best person to interpret them; The absence of changes in a CBC does not exclude the possibility of a disease. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
