A new blood test
for Lyme disease may provide a more accurate method for detecting the tick-borne
illness, particularly in its early stages when current tests may not yield
an accurate diagnosis.
A researcher from The Children's Hospital of Philadelphia has used a method that detects telltale proteins that often remain hidden from routine blood tests for Lyme disease.
In a patient who had a "bull's-eye" skin rash often found in early Lyme disease but who tested negative for the disease in three standard blood tests, the new test detected a protein called OspA.
OspA is an antigen, a substance that stimulates an immune response, and is produced specifically by Borrelia burgdorferi, the microorganism that causes Lyme disease.
The patient had already tested positive for Lyme disease after a culture was taken from a skin biopsy. However, this technique is performed only at a few specialized facilities, is more invasive than a blood test, and is not practical for large-scale testing.
"Our technique is practical for detecting the Lyme antigen in patients who test negative for the disease in the currently available blood tests," said Michael Brunner, Ph.D., of the Division of Rheumatology at The Children*s Hospital of Philadelphia. Dr. Brunner*s paper appears in the March issue of the Journal of Immunological Methods.
Although the results reported in the current paper describe a test in only one patient, the research builds on previous work by Dr. Brunner showing the presence of OspA in more than 20 patients with different stages of Lyme disease.
A recurrent worry for residents of the Northeastern U.S. and other regions, Lyme disease may present diagnostic puzzles. Other diseases, such as rheumatoid arthritis, may cause joint pains of the sort found in Lyme disease. The famous "bulls-eye" rash associated with Lyme disease occurs only in 60 to 80 percent of patients, and may fade before a patient sees a physician. For these reasons, along with inaccuracies in the current blood tests, Lyme disease has been called one of the most overdiagnosed and underdiagnosed illnesses.
Overdiagnosis occurs because current blood tests, which test for the disease indirectly by seeking antibodies produced by a patient's immune system, are not always specific for Lyme disease. Microorganisms not causing Lyme disease may give rise to the same antibodies, and false positive test results may occur. In addition, false positives may occur when a blood test detects residual antibodies to Lyme disease lingering in the blood long after the disease is cured.
However, false negatives may also occur because current blood tests for Lyme disease are not sensitive enough.
"Early in the disease, antibodies against Lyme disease may not be detectable because they are sequestered in immune complexes in the blood," says Dr. Brunner. In immune complexes, antigen from the invading microorganism binds to the antibodies that respond to the invasion.
The technique used by Dr. Brunner isolates the immune complexes from the patient's blood sample, captures the antibodies inside, then detaches and identifies the antigen -- the component that originated in the disease-causing microorganism.
"We identified at least one of the antigens as OspA, which is a smoking gun for Lyme disease," said Dr. Brunner. "The test can identify early disease, and also can distinguish active disease from evidence in the blood of a past disease."
Much additional work would be necessary to transform this finding into a large-scale, commercially available test. Additionally, said Dr. Brunner, the technique may be useful in studies of other diseases that exhibit immune complexes, such as lupus, infectious hepatitis and multiple sclerosis.
Founded in 1855 as
the nation's first pediatric hospital, The Children*s Hospital of Philadelphia
is ranked today as the best pediatric hospital in the nation by a comprehensive
Child Magazine survey. Its pediatric research program is among the largest
in the country, ranking second in National Institutes of Health funding.
- By Erin McDermott