Ticks And Lyme Disease Diagnostic Tests
In order to be diagnosed with Lyme disease, diagnostic tests are required. However, there won't always be positive results on a particular test if a patient does, in fact, have the disease. There are two primary reasons that an individual patient may need many different tests ordered. The first reason is that there may be other causes of the symptoms which must be ruled out before a diagnosis of Lyme disease can be made. Secondly, the cumulative results are considered and compared against the results of other patients with Lyme to see if they are consistent with each other.
The Western Blot and the ELISA are the two most common tests for Lyme disease. Both of these tests are used to look for the antibodies within the blood that are signs that the spirochete, B. burgdorferi, has caused an infection. The diagnosis is complicated by the fact that even if the antibodies are present, the infection may no longer be present in the body since the immune system continues to produce small amounts of the antibodies specific to Bb in order to re-call the response for many years. Because these tests are indirect, the results do not clearly reveal if the patient continues to be plagued with the infection.
a. Growing A Culture
The gold standard when it comes to evaluating infection is to grow a culture of the organism. In this case, the culture can take weeks since Borrelia burgdorferi is an organism that grows slowly. However, once the stage of erythema migrans has passed in the infection, the culture is rarely positive which makes this problematic. There are some studies indicating that positive culture results occur using certain methods of high volume blood collection, but in most cases it isn't necessary since the diagnosis of Lyme diseases can be made when the Erythema migrans rash is present and treatment can be initiated. Culture is rarely used because the test has low yields in late stage cases or when Lyme disease has been disseminated.
Widely used to screen for Lyme disease, the Enzyme Linked Immunosorbent Assay (ELISA) is automated and inexpensive. It reports a single number that reflects the amount of antibodies present in the serum of the patient compared to the agent of Lyme disease. For the ELISA assay, the whole cell sonicate of Bb is commonly used, but the results of this assay do come back with false positives and false negatives. With specificity rates as high as 80 to 100%, the C6 Peptide ELISA has been gaining in popularity as an assay for screening. There is considerable variance in the sensitivity of the Iimmunoflourescence assay (IFA) amd the ELISA with some estimates ranging between 55 and 90% depending upon the duration of infection and the clinical manifestations.
c. Western Blot
The Western Blot is a qualitative test unlike the quantitative tests, the IFA and the ELISA. The laboratory expert must have considerable skill in order to interpret the Western Blot by assessing each band's intensity to determine whether or not it can be considered to be absent or present. In order to remove subjective error, automated methods of assessment have been recently developed that evaluate the intensity of the band on a continuous basis as well as categorical information based on intensity cutoffs. In Europe and in the United States, the criteria used to evaluate the Western Blot vary. When five out of ten bands on the IgG or two out of three on the IgM are visible, then the Western Blot is interpreted as positive according to the standard method developed by the Centers for Disease Control that is used in the United States. The bands that are used for the IgG (18, 23, 28, 30, 39, 41, 45, 58, 66, 93) and the IgM (23, 39 or 41 kD) do not include the 31 kD and 34 kD bands that are well known to be specific for Bb.
d. Polymerase Chain Reaction (PCR)
The genetic material of an organism is detected in the PCR assay which makes them one of the most specific used for diagnostic purposes. The PCR looks at the DNA itself rather than looking at indirect evidence of infection by examining the response of the immune system with either the Western Blot or the ELISA. A very recent or a current infection is strongly suggested when the PCR results are positive, even though they cannot categorically state that a current infection does exist. However, when used to help diagnose Lyme disease, the results of the PCR assay are often negative. This might be because the Bb only lives within the blood for short amounts of time or because the genetic load in the specimen is below the level necessary for detection. Negative results may be obtained in the PCR assay done on CSF or the blood because Bb may reside in areas with reduced circulation since it is tissue tropic.
e. Other Laboratory Tests
Over the past twenty years, other methods of detecting Lyme disease have been explored including the Borreliacidal assay, the Lymphocyte Stimulation Assay, and the immune complex dissociation assay. These assays will not be discussed in detail because they have not been produced on a commercial basis. In recent reports, the Lyme urine antigen test and other assays have been questioned in regards to their effectiveness.