ELISA Test: Understanding the Enzyme-Linked Immunosorbent Assay

The ELISA test, short for Enzyme-Linked Immunosorbent Assay test, is a laboratory test that detects and analyses chemicals such as antibodies, hormones, proteins, and antigens in our blood.

It is an essential diagnostic tool in immunology and is known for its sensitivity, accuracy, and versatility.

Table of Contents

What is the ELISA Test?

The ELISA test is a type of immunoassay test which works by using antibodies and color changes to detect the presence of specific substances in a blood sample. It is most commonly used to:

Detect infections (e.g., HIV, Hepatitis B, COVID-19)
Identify allergens
Measure hormone levels (e.g., pregnancy tests)
Screen for autoimmune disorders

How Does ELISA Work?

The ELISA test involves several steps:

First step is Antigen Coating, which is the technique of coating a plate’s surface with the antigen (or antibody) to be evaluated.

Sample addition: A blood or serum sample is to be added, which will bind to the target substance (antigen or antibody) if it is present on the plate.

Enzyme-Linked Antibody: After addition of sample a secondary antibody bound to an enzyme is added which attaches to the main antibody-antigen complex.

Substrate Reaction: When a substrate is added, it reacts with the enzyme and produces a colour change.

Reading Results: The intensity of the color change is measured to determine the amount of the substance present.

There are different types of ELISA tests:

Direct ELISA: Combines a single antibody with an enzyme.

Indirect ELISA: In indirect Elisha procedure two antibodies (primary and secondary) are required.

Sandwich ELISA: This test detects antigens between two layers of antibodies.

Competitive ELISA: This procedure Measures the concentration of an antigen by detecting interference in binding.

What is the ELISA Test Used For?

The ELISA test has many medical and research uses:

1. Infectious Diseases

HIV/AIDS
Hepatitis B and C
Dengue
COVID-19

2. Autoimmune Disorders

Systemic lupus erythematosus (SLE)
Rheumatoid arthritis (RA)

3. Hormone Testing

Pregnancy (hCG levels)
Thyroid disorders

4. Allergy Testing

Food allergies
Environmental allergens

5. Cancer Markers

Some tumor markers like PSA for prostate cancer

How is the ELISA Test Performed?

Sample Collection: A healthcare provider draws a blood sample, usually from a vein in your arm.

Lab Analysis: The sample is sent to a lab where the ELISA procedure is carried out.

Result Interpretation: The colour intensity measured reflects the amount of target substance present.

ELISA Test Preparation

Usually, no fasting is required.
Inform your doctor about any medications or supplements you are currently using.
In case of specific hormone or allergy tests, some restrictions may apply.

ELISA Test Results

Positive Result: Indicates the presence of the target substance (e.g., infection or antibody).
Negative Result: Indicates the absence or below-threshold levels of the substance.

Sometimes, confirmatory tests like Western blot or PCR are needed for accurate diagnosis, especially in infectious disease cases.

ELISA Test Accuracy

ELISA is highly accurate but can occasionally give false positives or false negatives. This can happen due to:

Cross-reactivity with other substances
Early testing before the body produces detectable antibodies
To improve reliability, doctors often combine ELISA with other diagnostic tests.

ELISA Test Cost in India

In India, the cost of an ELISA test is depending on the purpose and the laboratory:

HIV ELISA Test: ₹500 – ₹1,000
Hepatitis ELISA: ₹800 – ₹1,500
Allergy Panel ELISA: ₹1,500 – ₹4,000
Hormone ELISA: ₹400 – ₹1,000

Advantages of ELISA

High sensitivity and specificity
Quick turnaround time
Cost-effective
Easy to automate and standardize

Limitations

May require follow-up tests for confirmation
Can be affected by sample handling and storage
The test may not detect very low levels at its early stages

Who Should Get an ELISA Test?

Your doctor may recommend an ELISA test if you:

Show symptoms of an infection
Need allergy testing
Are undergoing routine screening for HIV or Hepatitis
Have an autoimmune disease
Need hormone level assessment

Conclusion

The ELISA test is one of the most commonly used diagnostic tools in medicine. Whether it’s identifying infections, measuring hormone levels, or diagnosing immune system issues, this test plays a crucial role. Always consult with a healthcare professional to understand what your test results mean and whether further testing is necessary.

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Also Read:

Renal Function Test (RFT): Purpose, Normal Range & Results Explained

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