Complete Blood Count (CBC): What This Common Blood Test Measures and Why Your Doctor May Order It for You or Your Child

A complete blood count (CBC) is a routine blood test that measures the cells circulating in your blood, including red blood cells, white blood cells, and platelets. It also measures hemoglobin and hematocrit, which show how well your blood can carry oxygen throughout your body. Providers use this test as part of a general health check or to help evaluate a wide range of symptoms.

The Ocular Fluid Anaerobic Culture test is a laboratory test that detects and identifies anaerobic bacteria (bacteria that can live without oxygen) in fluid taken from the eye. Anaerobic bacteria are a common cause of serious eye infections that can lead to vision problems if not treated properly. This test helps doctors find the exact cause of your eye infection so they can prescribe the most effective treatment.

Your provider may order this test as part of a routine health exam, or to help find the cause of symptoms such as fatigue, weakness, fever, unusual bruising or bleeding, or signs of infection or inflammation. It can also be used to monitor a chronic condition such as anemia, or to check how your body is responding to certain treatments and medicines over time.

Your doctor may order this test if you have symptoms of a serious eye infection that has not responded to standard antibiotic treatment. Symptoms may include severe eye pain, redness, swelling, discharge, blurred vision, or sensitivity to light. The test is particularly important because anaerobic eye infections can be more severe and require specific antibiotics that are different from those used for regular bacterial infections.

A health professional will draw a small sample of blood, usually from a vein on the inside of your elbow or the back of your hand. The site is cleaned with an antiseptic, an elastic band is placed around your upper arm, and a thin needle collects the sample into a tube. You may feel a quick sting, and the process usually takes only a few minutes. Afterward, a small bandage is applied, and you can return to your normal activities right away.

An eye specialist (ophthalmologist) will collect a small sample of fluid from your eye using a thin, sterile needle. This procedure is called ocular fluid aspiration or paracentesis. The area will be numbed with eye drops to minimize discomfort. After collection, the fluid is placed in a special container that prevents oxygen exposure and sent to the laboratory for analysis.

Results show whether your blood cell counts fall within the normal range. A low red blood cell count may point to anemia, while high values can occur with dehydration. A high white blood cell count may suggest infection or inflammation, and a low count can affect your ability to fight infection. Platelet results help show how well your blood clots. Your provider will review your numbers along with your symptoms and medical history, so ask them what your specific results mean for you.

A positive result means anaerobic bacteria were found in your eye fluid, which confirms an anaerobic bacterial eye infection. The laboratory will also perform antibiotic sensitivity testing to determine which antibiotics will work best against the specific bacteria found. A negative result means no anaerobic bacteria were detected, but this does not completely rule out infection—your doctor will consider your symptoms and other test results to make a final diagnosis.