Elisa Test for Lyme Disease: Everything You Need to Know
Are you concerned about Lyme disease and worried about how to get an accurate diagnosis? Look no further!
Lyme disease can have serious health implications if not diagnosed and treated promptly. The Elisa test is a commonly used blood test that helps detect Lyme disease by measuring the presence of specific antibodies in the bloodstream.
In this comprehensive guide, we'll walk you through the entire process from how the test works, its accuracy and limitations, to what you can expect during and after the test. We'll also explore the importance of interpreting the test results correctly and why it's essential to consult with a healthcare professional for proper diagnosis and treatment.
So, read on to become an informed advocate for your well-being.
What is the Elisa test?
Lyme disease, a tick-borne illness, can be a complex and challenging diagnosis. Thankfully, the ELISA test plays a vital role in identifying the presence of antibodies to the Borrelia burgdorferi bacteria, the culprit behind Lyme disease. This screening test is often the first step in diagnosis, offering a valuable tool for healthcare professionals.
The ELISA test is also known as the enzyme-linked immunosorbent assay. It detects the presence of antibodies produced by your body in response to a potential Lyme disease infection. These antibodies are like soldiers fighting the invading bacteria, and their presence indicates exposure to the disease.
How does the Elisa test work?
The Elisa test is a highly sensitive and versatile laboratory technique used to detect and measure the presence of antibodies, antigens, proteins, and hormones in various bodily fluids like blood, urine, and saliva. Here are the details of the test:
1. Sample Preparation
The first step involves drawing a blood sample from the patient. This sample is then centrifuged to separate the serum, the liquid portion containing the antibodies we're interested in. The serum is then diluted to a specific concentration to ensure accurate results.
2. Antigen Coating
The wells of a microtiter plate, similar to a miniature egg carton, are coated with Lyme disease antigens. These antigens are essentially proteins derived from the Borrelia burgdorferi bacteria. The coated plate is then incubated to allow the antigens to firmly adhere to the wells, providing a foundation for the subsequent steps.
3. Antibody Binding
Now comes the heart of the test. The diluted serum sample is added to the wells containing the coated antigens. If antibodies specific to Lyme disease are present in the serum, they will bind to the corresponding antigens on the plate's surface. This binding process is like a lock and key mechanism, where only the right antibodies can fit with their specific antigens. The plate is then incubated again, allowing ample time for this crucial interaction to occur.
4. Washing
After the incubation period, the plate is thoroughly washed to remove any unbound serum components. This ensures that only the antibodies that have successfully bound to the antigens remain on the plate, preventing interference from other substances in the serum.
5. Enzyme-Linked Antibody Detection
This step introduces an enzyme-linked secondary antibody. This helper antibody specifically binds to the human antibodies that are already attached to the Lyme disease antigens on the plate. The result is a sandwich-like structure, with the primary antibody from the patient's serum sandwiched between the antigen and the enzyme-linked secondary antibody.
6. Substrate Addition and Color Development
A colorless substrate solution is then added to the wells. This substrate acts as a fuel for the enzyme linked to the secondary antibody. When the enzyme interacts with the substrate, it catalyzes a reaction that causes the substrate to change color. The intensity of this color change is directly proportional to the amount of antibodies present in the patient's serum. In simpler terms, the more antibodies present, the deeper the color becomes.
7. Measurement and Interpretation
After the color development process is complete, the intensity of the color in each well is measured using a specialized instrument called a plate reader. This instrument provides quantitative data that can be compared to a standard curve. Based on this comparison, the concentration of Lyme disease antibodies in the patient's serum can be determined.
8. Reporting and Interpretation of Results
The results of the ELISA test are typically reported as positive, negative, or indeterminate. A positive result indicates that antibodies to Lyme disease were detected, suggesting possible infection. However, additional tests like the Western blot may be needed for confirmation. A negative result suggests a low likelihood of Lyme disease, while an indeterminate result requires further investigation.
Accuracy and reliability of the Elisa test
A systematic review and meta-analysis of North American research reported that the sensitivities of in-house ELISAs varied from 0–86%. Similarly, a systematic review and meta-analysis of serological tests for Lyme borreliosis in Europe found that the accuracy of the ELISA varied, with specificity around 95% in studies with healthy controls, but around 80% in cross-sectional studies.
The CDC also emphasizes that the accuracy of the test depends on how long the individual has been infected, and during the first few weeks of infection, the test is expected to be negative. Therefore, while the ELISA is a valuable tool for Lyme disease diagnosis, it is important to consider its limitations and the timing of the test in relation to the onset of symptoms.
Limitations and potential false positives/negatives
The ELISA test is a commonly used diagnostic tool for Lyme disease, but it has some limitations and can produce false positive and false negative results. Some of these limitations include:
Sensitivity
The sensitivity of ELISA tests can be low, especially during the early stages of Lyme disease. It may take several weeks for antibodies to develop, so tests performed before this time may be negative even if the person is infected
Specificity
The specificity of ELISA tests is generally high, around 95% in studies with healthy controls. However, the specificity can be lower in cross-sectional studies, around 80%.
Accuracy
The accuracy of the test depends on the duration of infection. During the first few weeks of infection, the test is expected to be negative, such as when a patient has an erythema migrans rash.
Two-tier testing
Some experts recommend using a two-tier testing approach, which involves performing an initial ELISA test followed by a confirmatory test (e.g., Western blot) if the ELISA test is positive. However, the accuracy of two-tier testing is not always superior to using a single test approach.
In-house ELISAs
The accuracy of in-house ELISAs can vary, with sensitivities ranging from 0–86%. These tests often have small sample sizes and may not be as reliable as commercially available tests.
Potential false positives/negatives
False Positives
False positives in ELISA can arise due to various factors. Non-specific binding occurs when the capture or detection antibodies bind to substances other than the target antigen, such as contaminants in the sample or other proteins.
Cross-reactivity is another challenge, where antibodies may recognize similar antigens, leading to a positive result even in the absence of the target antigen. Inadequate washing during the assay can result in the retention of unbound proteins, contributing to non-specific binding. High background signals may occur due to reagent contamination or issues with the microtiter plate.
Additionally, endogenous enzyme activity in samples can interfere with the ELISA reaction, causing false positives. The hook effect is observed when an excessively high concentration of the target antigen overwhelms the capture antibody, resulting in a false negative outcome.
False Negatives
False negatives can be attributed to factors such as insufficient antibody concentration, inadequate incubation time for the sample, or improper storage and handling of samples leading to degradation.
Weak interactions between the antigen and antibody can also result in a false negative result, as the ELISA may not detect the binding effectively. Inhibition by certain substances in the sample can prevent the antibody from binding to the antigen, leading to false negatives. The prozone effect is a phenomenon where an extremely high concentration of the target antigen competes with the antigen bound to the capture antibody, causing a false negative outcome. Understanding these limitations is crucial for accurate interpretation of ELISA results and optimizing assay conditions.
Alternative tests for Lyme disease
Western Blot: This test is commonly used as a follow-up to the ELISA. It can help confirm the diagnosis if the ELISA is positive. The Western blot detects the presence of antibodies to the Lyme disease bacteria.
Urine Antigen Tests
These tests have been shown to be inaccurate and are not recommended for routine use.
CD57 Tests
These tests have also been shown to be inaccurate and are not recommended for routine use.
Two-tiered Testing Approach
This approach involves performing an initial ELISA test followed by a confirmatory test, such as the Western blot, if the ELISA is positive. This two-tiered approach is commonly used for Lyme disease diagnosis.
Brain Imaging Tests, Neurocognitive Tests, and Nerve Conduction Studies
These tests may be used when central nervous system Lyme disease is suspected. They can help in the diagnosis of neurological complications of Lyme disease
Conclusion
ELISA test is considered reliable but it is not 100% accurate. Though the alternative tests exist, the diagnosis of Lyme disease should be based on a combination of clinical evaluation, patient history, and laboratory test results. The interpretation of these tests should be done in the broader context of a person's illness and medical history