Babesiosis; Human granulocytic anaplasmosis (HGA)
Proper diagnosis of Lyme disease is important. A diagnosis of Lyme disease is straightforward if the patient meets the following criteria:
If the patient meets all the criteria, except the rash, the doctor may undertake the enzyme-linked immunosorbent assay (ELISA) or the Western Blot test.
In a few cases, if the patient seeks a diagnosis within the first 2 - 3 weeks, the doctor may take a sample of the skin or of the blood. If Lyme spirochete is present, it may be identified in the laboratory in a culture medium (a substance in which the organism can thrive and reproduce). This is necessary only if a doctor suspects Lyme but the diagnosis is not clear.
If the infection is not obvious from the patient's history and physical symptoms, but Lyme disease is suspected, the doctor may run tests for evidence of specific factors that suggest infection with B. burgdorferi. Such factors include:
The U.S. Centers for Disease Control (CDC) recommends a two-step process for Lyme disease blood tests:
The CDC recommends only these tests. Other tests -- such as urine antigen, immunofluroescent staining, and lymphocyte transformation -- do not have enough scientific evidence to support their use.
Accuracy of the Tests. These tests are very expensive, and none are completely accurate in either identifying Lyme or ruling it out. They should never be used to make a primary diagnosis of Lyme disease in patients who do not have obvious symptoms of the disease.
Both false positive and false negative results are common with these tests.
False positive results occur when the test suggests the presence of the disease, but the person does not actually have an active infection. This may occur in different ways:
False negative results miss the actual presence of the disease. These results are also common. (If the results are negative but Lyme disease is highly suspected, the doctor will probably prescribe antibiotics anyway.) False negative results occur for a number of reasons:
All of this means that a negative blood test does not rule out a diagnosis of Lyme disease, particularly if symptoms strongly suggest its presence. Conversely, a positive blood test does not prove that Lyme disease is causing the symptoms. A second blood test, taken several weeks later, may help.
The polymerase chain reaction (PCR) test detects the DNA of the bacteria that causes Lyme disease. However, it requires technical expertise and expensive equipment, and can be performed only in a few laboratories in the country. The test also has a high risk of false-positive results. Research indicates that blood or urine samples do not provide accurate results, but skin biopsies may be useful in some cases. At this point, the PCR test is reserved for certain patients with specific diagnostic problems. For most patients, standard antibody tests are preferred.
Analysis of Spinal Fluid. In patients who have neurologic symptoms, a lumbar puncture (a spinal tap) may be used to test for the bacteria in spinal fluid and may be useful for an early diagnosis of Lyme disease.
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