Complete Blood Count (CBC): What You Need to Know About This Common Blood Test

The complete blood count, commonly called a CBC, is one of the most frequently ordered blood tests. It measures the different cells that make up your blood, including red blood cells, white blood cells, and platelets, and gives your health care team a broad picture of your overall health.

This test measures two important components in your cerebrospinal fluid (CSF): beta-2 globulin and total protein. Cerebrospinal fluid is a clear, protective liquid that surrounds your brain and spinal cord. The test uses a technique called electrophoresis, which separates different protein types in the fluid so they can be measured individually.

This test is performed to screen for and help diagnose a wide range of conditions, such as anemia, infections, inflammation, and problems with blood clotting. Your doctor may order it as part of a routine checkup, to investigate symptoms like fatigue, weakness, or fever, or to monitor an existing condition or ongoing treatment.

Your doctor may order this test if you have symptoms suggesting a problem with your brain or nervous system, such as severe headaches, neck stiffness, confusion, or numbness. The test helps identify conditions that affect the central nervous system, including infections (like meningitis or encephalitis), inflammatory diseases (such as multiple sclerosis), bleeding in the brain, or tumors. By analyzing the protein patterns in your CSF, doctors can better understand what might be causing your symptoms.

The sample is collected through a simple blood draw, usually from a vein on the inside of your elbow or the back of your hand. A health care professional cleans the area, wraps a band around your upper arm, and draws a small amount of blood into a tube with a thin needle. The procedure typically takes only a few minutes, and you may feel a brief pinch.

The sample is collected through a procedure called a lumbar puncture, also known as a spinal tap. During this procedure, you will lie on your side or sit up while a healthcare provider inserts a thin needle between two vertebrae in your lower spine to collect a small amount of CSF. The area will be numbed with local anesthetic to minimize discomfort. The procedure usually takes about 15-30 minutes, and you may be asked to lie flat for a short time afterward to reduce the chance of a headache.

The results show whether the number, size, and features of your blood cells fall within normal ranges. Values that are too high or too low can point to conditions such as anemia, infection, dehydration, or clotting disorders, but a single abnormal value does not always mean you are sick. Your doctor will interpret the results together with your symptoms, medical history, and other tests to determine whether further evaluation or treatment is needed.

Normal CSF contains a small amount of protein, including various globulin fractions. Abnormal results may show increased total protein or changes in the beta-2 globulin fraction. Elevated protein levels may indicate infection, inflammation, bleeding, tumors, or demyelinating diseases like multiple sclerosis. Your doctor will interpret your results along with your symptoms and other test findings to determine what they mean for your health.