Does this test have other names?

Cat scratch disease blood test, indirect fluorescent antibody test (IFA) for IgM and IgG against B. henselae

What is this test?

This blood test screens for exposure to B. henselae (Bartonella henselae), the bacteria that cause cat scratch disease. These bacteria are spread by cats, especially kittens, which are more likely to be infected. The disease is often fairly mild and clears up without treatment. But it can be more serious for people with a weakened immune system.

If you are infected by B. henselae, your immune system may form proteins called antibodies to fight the infection. One way to diagnose cat scratch disease is to check your blood for these antibodies. 

Why do I need this test?

You may need this test if you have been scratched or bitten by a cat and have symptoms of cat scratch disease. Even if you have only been in close contact with a cat or cat fleas, you may have the test if you have symptoms of the disease. Common symptoms of cat scratch disease include:

• Infected or swollen scratch or bite

• Skin rash

• Swollen lymph nodes around your head, neck, or armpits

• Fever

• Headache

• Severe tiredness (fatigue)

• Loss of appetite

• Muscle aches

• Belly (abdominal) pain

• Weight loss

What other tests might I have along with this test?

In rare cases, your healthcare provider may need to take a lymph node sample (biopsy). The sample will be looked at under a microscope for the bacteria that causes cat scratch disease. 

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

Having a positive test for cat scratch antibodies doesn't always mean you have an active infection. But it does mean that you have been exposed to the bacteria. This test will look for antibodies called immunoglobulin G (IgG) and immunoglobulin M (IgM). These antibodies are measured in titers. A titer less than 1:64 suggests that you don't have a current infection. You may have or have had cat scratch disease if:

• You have a single elevated titer

• You have an IgG titer of less than 1:64. This means you don't have active infection but may have had an infection in the past. 

• You have an IgG titer greater than 1:64 but less than 1:256. This result means a possible infection. You may need another test in 10 to 14 days.

• You have an IgG titer greater than 1:256, which suggests active or recent infection

• You have a positive test for IgM. This suggests an active (acute) disease or a very recent infection.

A negative test won't rule out the disease if your healthcare provider strongly believes that you have the disease. (See symptoms listed above.) Your provider will decide if you need to be treated for cat scratch disease based on your blood test, any other diagnostic tests, and your symptoms. 

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

What might affect my test results?

Finding antibodies to B. henselae is a reliable way of diagnosing cat scratch disease. But you may have symptoms before your antibodies get high enough to detect. You might need to have this blood test repeated over time.

How do I get ready for this test?

You don't need to prepare for this test. Tell your healthcare provider about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.