Blood Test: What to Expect and How to Understand Your Results

This test involves taking a small sample of your blood so it can be examined in a laboratory. The measurements your provider orders can help evaluate how well your organs are working, look for signs of illness, or track a medical condition you already know you have.

This test looks for antibodies in your blood that your immune system makes in response to Borrelia bacteria, which cause Lyme disease. The test detects two types of antibodies: IgM (which appear first, usually within 2-4 weeks) and IgG (which develop later, often after several weeks to months). It tests for three species of Borrelia that can cause Lyme disease: Borrelia burgdorferi, Borrelia afzelii, and Borrelia garinii.

Your doctor may order this test as part of a routine checkup, to help find the cause of symptoms you are having, to screen for health problems before they cause symptoms, or to see how well a treatment is working over time.

Your healthcare provider may order this test if you have symptoms of Lyme disease, especially if you have been bitten by a tick or have been in areas where Lyme disease is common. Common symptoms include a bull's-eye rash (erythema migrans), fever, headache, fatigue, and muscle or joint pain. Early detection and treatment are important to prevent complications.

A trained healthcare professional will clean your skin, usually on the inside of your elbow, and use a small needle to draw blood into a collection tube. The procedure takes only a few minutes, and you may feel a brief sting when the needle goes in.

A healthcare professional will draw a blood sample from a vein in your arm. The sample is then sent to a laboratory where it is tested using an immunoassay method to detect the presence and levels of IgG and IgM antibodies against Borrelia bacteria.

Your results are compared with typical reference ranges. Values outside these ranges may suggest a condition that needs further testing, but medicines, diet, hydration, and other factors can affect the numbers, so always review your results with your provider.

A positive result indicates that antibodies to Lyme disease bacteria were detected, suggesting a current or past infection. However, results must be interpreted carefully: (1) A positive IgM with negative IgG may indicate early infection, (2) Positive IgG with negative IgM may indicate later or past infection, (3) Both positive suggests ongoing or recent infection. Some people may have false positives due to other conditions, so your doctor will consider your symptoms, exposure history, and may order additional tests.