Complete Blood Count (CBC) Test

A complete blood count, commonly called a CBC, is a routine blood test that measures and evaluates the cells circulating in your blood, including red blood cells, white blood cells, and platelets, giving your healthcare provider a broad picture of your overall health and how well your body is working.

This test looks for IgG antibodies in your blood that specifically target your neutrophils (a type of white blood cell). These antibodies can develop when your immune system reacts to amoxicillin, a commonly prescribed antibiotic. The test uses flow cytometry, a specialized laboratory technique that can detect these antibodies on the surface of your neutrophils.

Your provider may order this test as part of a regular checkup, or to help investigate symptoms such as fatigue, weakness, fever, pale skin, or unusual bruising and bleeding, because it can help detect conditions like infection, anemia, inflammation, and certain blood disorders.

Your doctor may order this test if you are taking amoxicillin and develop symptoms such as fever, sore throat, mouth ulcers, or frequent infections. These symptoms may indicate neutropenia (low neutrophil count), which can be a rare side effect of amoxicillin. The test helps determine whether amoxicillin is causing your body to attack its own neutrophils.

The test is done with a simple blood draw: a healthcare professional cleans a small area of your arm, wraps a band around your upper arm, inserts a thin needle into a vein, and collects a sample into one or more tubes, a process that usually takes only a few minutes and may cause brief discomfort.

A healthcare professional will draw a blood sample from a vein in your arm. The blood will be sent to a laboratory where technicians will use flow cytometry to detect the presence of IgG antibodies attached to your neutrophils. You do not need to fast or prepare specially for this test.

Your results show whether your blood cell counts and characteristics fall within normal reference ranges; values that are too high or too low may suggest problems such as infection, anemia, dehydration, or clotting issues, and your healthcare provider will explain what your specific numbers mean for your health.

A positive result indicates that IgG antibodies against neutrophils were detected in your blood, suggesting that amoxicillin may be causing your immune system to attack your white blood cells. A negative result means no such antibodies were found, and your neutropenia may have another cause. Your doctor will interpret these results along with your symptoms and other test results to determine the best course of treatment.