Complete Blood Count (CBC)

A complete blood count, or CBC, is a common blood test that measures the different cells in your blood, including red blood cells, white blood cells, and platelets. It gives your healthcare provider important information about your overall health and can help detect a wide range of conditions, from infections and anemia to certain blood disorders.

This test looks for IgM antibodies in your blood that target your own neutrophils (a type of white blood cell) after you take aspirin. Neutrophils are important for fighting infections. When the immune system produces antibodies against them, it can lead to a condition called neutropenia, where the body has too few neutrophils to properly fight off germs.

Your provider may order this test as part of a routine checkup, or to help evaluate symptoms such as fatigue, weakness, fever, bruising, or unexplained bleeding. It can also be used to monitor an existing condition, such as anemia, or to check how your body is responding to a treatment, such as chemotherapy or certain medicines.

Your doctor may order this test if you have symptoms suggesting an adverse reaction to aspirin, such as: unexplained fever, frequent infections, unusual bruising or bleeding, or abnormal blood test results showing low white blood cell counts. It may also be used to evaluate patients with known aspirin sensitivity or those with certain autoimmune conditions.

A small sample of blood is drawn from a vein, usually in your arm. A healthcare provider will clean the site, wrap a band around your upper arm, and insert a thin needle to collect the blood into a tube. The sample is then sent to a laboratory, where it is analyzed to measure the number, size, and types of blood cells. The test usually takes only a few minutes.

A healthcare professional will draw a blood sample from a vein in your arm. The blood is then sent to a laboratory where special techniques (flow cytometry) are used to detect the presence of IgM antibodies that react to neutrophils in the presence of aspirin. You may be asked to undergo testing before and after taking a controlled dose of aspirin to see if antibodies are induced.

Your results will show whether your red blood cells, white blood cells, and platelets are within normal ranges. A low red blood cell count may suggest anemia, while a high white blood cell count can point to an infection or inflammation. Abnormal platelet levels may affect how well your blood clots. Your provider will review the results with you and explain what they mean in the context of your symptoms and overall health.

A positive result indicates that IgM antibodies against neutrophils were detected after aspirin exposure, suggesting an immune-mediated reaction to aspirin. A negative result means no antibodies were detected. Your doctor will interpret these results along with your symptoms and other test findings to determine the appropriate treatment plan.

This test has very few risks. You may feel a brief sting or pinch when the needle goes in, and the site may be slightly sore or bruised for a day or two. Serious problems, such as infection or heavy bleeding, are rare. Tell your provider if you have a bleeding disorder or take blood thinners, as this may affect the blood draw.

The blood draw may cause slight bruising, soreness, or dizziness. These risks are minimal. If the test involves taking aspirin under medical supervision, your doctor will monitor you for any adverse reactions.