Your health care provider may have difficulty diagnosing Lyme disease because many of its symptoms are similar to those of other disorders. In addition, the only distinctive sign unique to Lyme disease-the EM rash-is absent in at least one-fourth of the people who become infected.

The results of recent research studies show that an infected tick must be attached to the skin for at least 2 days to transmit Lyme bacteria. Although a tick bite is an important clue for diagnosis, many people cannot recall having been bitten recently by a tick. This is not surprising because the deer tick is tiny, and a tick bite is usually painless.

If you have possible Lyme disease symptoms, but do not develop the distinctive rash, your health care provider will rely on a detailed medical history and a careful physical examination for clues to diagnose it, with laboratory tests to support the diagnosis.

Blood Tests

The Lyme disease bacterium is difficult to find in laboratory tests of body tissues or fluids. Therefore, most health care providers look for evidence of antibodies against B. burgdorferi in the blood to confirm the bacterium's role as the cause of symptoms.

Some people with nervous system symptoms also may get a spinal tap. Using this procedure, your health care provider can detect brain and spinal cord inflammation and can look for antibodies or genetic material of B. burgdorferi in the spinal fluid.

Health care providers cannot always firmly establish whether Lyme disease bacteria are causing symptoms. In the first few weeks following infection, antibody tests are not reliable because your immune system has not produced enough antibodies to be detected. Antibiotics given early during infection also may prevent antibodies from reaching detectable levels, even though Lyme disease bacteria are causing your symptoms.

The antibody test most often used is called an ELISA (enzyme-linked immunosorbent assay) test. The Food and Drug Administration has approved two antibody tests;

• Prevue B, a rapid test, can give results within an hour
• The C6 Lyme Peptide ELISA is very sensitive and specific

If your ELISA is positive, your health care provider should confirm it with a second, more specific test called a Western blot.

Health care providers must rely on their clinical judgment in diagnosing Lyme disease if you don't have the distinctive EM rash. Such a diagnosis would be based on;

• Time of year
• History of a tick bite
• Symptoms

In addition, your health care provider will rule out other diseases that might cause your symptoms. Health care providers may consider factors such as;

• Whether your symptoms first appeared during the summer months when tick bites are most likely to occur
• Whether you were outdoors in an area where Lyme disease is common

New Tests Under Development

Health care providers need tests to distinguish between people who have recovered from previous infection and those who continue to suffer from active infection.

To improve the accuracy of Lyme disease diagnosis, National Institutes of Health (NIH)-supported researchers are re-evaluating existing tests and developing a number of new tests that promise to be more reliable than those currently available.

NIH scientists are developing tests that use the highly sensitive genetic engineering technique known as PCR (polymerase chain reaction) as well as microarray technology to detect extremely small quantities of the genetic material of the Lyme disease bacterium or its products in body tissues and fluids.

A bacterial protein, outer surface protein (Osp) C, is proving useful for early detection of specific antibodies in people with Lyme disease. Since the genome of B. burgdorferi has been sequenced, new avenues are available for improving understanding of the disease and its diagnosis.