Complete Blood Count (CBC) Test: Overview, Sample Collection, Reasons for Testing, and Understanding Your Results

What is this test? A complete blood count, or CBC, is a common blood test that measures the cells circulating in your blood, including red blood cells, white blood cells, and platelets, and helps your provider evaluate your overall health.

A nasopharyngeal bacterial culture is a laboratory test that collects a sample from the upper part of the throat, behind the nose. The sample is placed in a special environment that allows aerobic bacteria (bacteria that need oxygen to grow) to multiply. Laboratory technicians then identify which types of bacteria are present and determine if they may be causing your illness.

How is the sample collected? A health care professional will clean the skin on your arm, then draw a small amount of blood from a vein, usually in your inner elbow, using a thin needle; the procedure takes only a few minutes.

A healthcare professional will use a sterile swab to gently collect a sample from the back of your throat or nasopharynx area. This may cause a brief gagging sensation but is generally quick and not painful. The swab is then placed in a sterile container and sent to the laboratory for analysis.

Why might I need this test? Your provider may order a CBC as part of a routine checkup, to look into symptoms such as fatigue, weakness, fever, bruising, or unusual bleeding, or to monitor conditions like anemia, infection, or certain treatments.

Your doctor may order this test if you have symptoms of a respiratory infection such as persistent sore throat, fever, cough, or difficulty breathing. It helps distinguish between viral and bacterial infections, as treatment differs significantly. This test is particularly useful for diagnosing conditions like strep throat, bacterial pneumonia, or identifying carriers of harmful bacteria.

What do the results mean? Your results show whether your red blood cell, white blood cell, and platelet counts fall within normal ranges; abnormal values may point to anemia, infection, inflammation, or clotting problems, and your provider will explain what they mean for you.

Results will show which bacteria, if any, were found in your sample. A 'negative' result means no pathogenic bacteria were identified. A 'positive' result indicates that bacteria were found and identified. Your doctor will interpret these results along with your symptoms and medical history to determine the best treatment plan, including whether antibiotics are needed.