Complete Blood Count (CBC): What This Common Blood Test Measures and When It Is Used

The complete blood count, or CBC, is a routine blood test that measures the different cells circulating in your blood, including red blood cells, white blood cells, and platelets, along with several related values that help describe how well those cells are working.

The Borrelia burgdorferi IgM Antibody test is a blood test that detects IgM (immunoglobulin M) antibodies against the bacterium Borrelia burgdorferi, which causes Lyme disease. Lyme disease is typically transmitted through the bite of infected blacklegged ticks (Ixodes scapularis) found in certain regions of the United States and Europe.

Your doctor may order this test as part of a regular checkup, to look into symptoms such as tiredness, weakness, fever, or unusual bruising and bleeding, or to keep track of an ongoing health condition or how a treatment, such as a medication, is affecting your body.

This test is ordered when you have symptoms suggestive of early Lyme disease, especially if you have a known or suspected tick bite or have been in areas where Lyme disease is common. Early symptoms may include the characteristic 'bull's-eye' rash (erythema migrans), fever, headache, fatigue, and muscle aches. The IgM antibody test is most useful during the early stages of infection (first 4-6 weeks) when IgG antibodies may not yet be detectable.

Your results are compared with standard reference ranges. Values that are higher or lower than normal can suggest conditions such as anemia, infection, inflammation, or problems with clotting, but a single result rarely gives a final diagnosis. Your doctor will review your full results with you and explain what the numbers mean in your situation.

Results are typically reported as positive, negative, or equivocal (uncertain). A positive or borderline IgM result, combined with symptoms and exposure history, suggests early Lyme disease infection. A negative result does not completely rule out Lyme disease, especially if the infection is very recent—the body needs time to produce detectable antibodies. Your healthcare provider may recommend repeat testing in 2-4 weeks if symptoms persist.

A trained health professional will clean a small spot on your arm, usually on the inside of the elbow, and draw a small sample of blood from a vein with a thin needle. The procedure normally takes only a few minutes, and the sample is then sent to a laboratory where a machine counts and measures your blood cells.

A healthcare professional will draw a blood sample from a vein in your arm. The procedure takes only a few minutes. You may feel a brief sting or pinch when the needle is inserted. The blood sample is then sent to a laboratory for analysis.

This test is very safe and routine. Most people feel only a brief sting or pinch when the needle goes in, and some notice mild soreness or a small bruise at the puncture site for a day or two. Serious complications, such as infection or heavy bleeding, are extremely rare.

The risks of this blood test are minimal and include slight pain or bruising at the injection site, lightheadedness, and in rare cases, infection. These risks are generally minor and temporary.