One of the most common tests that doctors order is a complete blood count (CBC), in which blood is drawn from a vein in the patient's arm. Some doctors order a blood panel during a routine checkup, while others only do so when patients complain of symptoms, such as fatigue or excessive bleeding. This is because this type of screening allows doctors to diagnose various conditions, including infections, diseases and side effects of medications. Doctors tend to pay a lot of attention to both the white and red blood cell counts. They also can use the complete blood count results to find out more about the platelets and hemoglobin in the patient.
White blood cells are considered an important aspect of a complete blood count, because an abnormal number of these shows that the body is likely fighting an infection. Therefore, a full blood exam counts the number of white blood cells and also considers the types that are present, which is done by analyzing the size and shape of each cell. Doctors can usually spot an infection after looking at the information gathered about the white blood cells during a complete blood count. They also can determine the side effects of certain medications on the body, because some drugs cause an abnormal number of white blood cells.
Another aspect of a full blood count to which doctors pay attention is red blood cells. A CBC counts the number of red blood cells, and analyzes both the size of these cells and variations in the size. In addition, a CBC measures the amount of hemoglobin in red blood cells, because this substance is meant to help distribute oxygen to the entire body. A low level of hemoglobin can lead to anemia, which often causes patients to feel constantly tired and bruise easily. Therefore, patients complaining of these symptoms are often given a CBC so their doctor can diagnose and treat them as soon as possible.
Platelets also are measured during a complete blood count, because they are important in stopping bleeding. Thus, patients who notice excessive bleeding without clotting may have to get a blood panel so their doctor can diagnose and treat the issue. This kind of test not only analyzes the number of platelets, but also the size, because smaller platelets are generally older. Therefore, results that show mostly small platelets may indicate reduced production of this cell, signaling a problem.