Complete Blood Count (CBC) Test: What It Is and What Your Results Mean

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, platelets, hemoglobin, and hematocrit. These cells carry oxygen, fight infection, and help your blood clot properly.

An anaerobic bacterial culture is a laboratory test that finds and identifies bacteria that can grow without oxygen (anaerobic bacteria) in a sample of pus. Pus is a thick, yellowish fluid that forms at the site of an infection. This test is different from regular bacterial cultures because anaerobic bacteria require special conditions to grow—they cannot survive in the presence of oxygen.

Your doctor may order a CBC as part of a routine checkup or to look into symptoms such as fatigue, weakness, fever, easy bruising, or unexplained weight loss. It can help detect anemia, infections, clotting problems, and certain blood disorders, and it can also be used to monitor ongoing treatments or how a condition is responding to therapy.

Your doctor may order this test if you have signs of a serious infection, especially if it is deep in the body. Anaerobic bacteria often cause infections in areas with low oxygen, such as abscesses, infected wounds, dental infections, abdominal infections, lung infections, or infections after surgery. Finding the exact bacteria helps your doctor give you the right treatment.

The sample is collected by drawing a small amount of blood from a vein, usually in your arm. A trained professional will clean the site, wrap a band around your upper arm, and insert a thin needle to collect the blood into a small tube. The procedure takes only a few minutes, and you may feel a brief sting when the needle goes in.

A healthcare provider will collect pus from your infection using a sterile swab, needle, or syringe. The area will be cleaned to avoid contamination. For deep infections, the provider may need to drain an abscess to get a good sample. The sample is then placed in a special container that does not contain oxygen and sent to the laboratory for testing.

In the laboratory, your blood sample is placed into an automated analyzer that counts and measures each type of blood cell. If any result looks unusual, a laboratory scientist may examine a stained slide of your blood under a microscope to confirm the findings before they are reported.

In the lab, scientists place the pus sample onto special culture plates and in containers that create an oxygen-free environment. They wait for bacteria to grow, which can take several days. Once bacteria grow, they are identified through various tests. The lab may also test which antibiotics can kill the bacteria (sensitivity or susceptibility testing).

Your results show whether your blood cell counts fall within the normal reference ranges. High or low values can point to conditions such as anemia, infection, inflammation, or bleeding disorders, but a single abnormal value does not always mean you are ill. Your doctor will interpret your results along with your symptoms, medical history, and other tests to decide what follow-up care you need.

A positive result means anaerobic bacteria were found and identified. Your doctor will use this information to choose the most effective antibiotic. A negative result means no anaerobic bacteria were found, but this does not always mean there is no infection—other types of bacteria or non-infectious causes may be responsible. Your doctor will interpret the results together with your symptoms and other test results.