ELISA kits are one of the most versatile immunoassays used in research and diagnostic laboratories to detect and quantify different analytes. However, faced with the growing need to detect analytes present in very low concentrations, these assays have shown some limitations in terms of sensitivity.
The development of variations on traditional ELISAs like the CLIA assays solves this limitation.
This type of immunoassay includes a chemiluminescent detection system that makes it more sensitive.
MAIN CHARACTERISTICS OF ELISA AND CLIA TESTS
Before analysing the differences between ELISA and CLIA assays, let´s look at some characteristics of each of these immunoassays:
ELISA Immunoassay
These assays use antibodies conjugated to an enzyme that, once the corresponding chromogenic substrate is added, catalyses a chemical reaction producing a visible and quantifiable colour change in the sample.
ELISA assays can be used both to detect the presence of an analyte in the sample (qualitative) and to measure the concentration at which it is found (quantitative). In this latter case, it is necessary to generate a standard curve by using known antigen concentrations.
CLIA immunoassay
In recent years, CLIA assays have gained ground in fields such as biomedical research, clinical diagnosis, food safety, and pharmaceutical analysis, among others, due to their high sensitivity and specificity.
CLIA assays are based on the same technical foundation as ELISA, with the difference that in this case, the enzyme coupled to the detection antibody catalyses a chemiluminescent reaction that results in the emission of photons producing light instead of a visible colour change.
Compared to other analytical methods, luminometry provides exceptionally high sensitivity (1pg/ml) with a wide detection range and the use of inexpensive instrumentation.
Differences between ELISA and CLIA assays
We can characterize the differences between these types of assays based on the type of substrate and signal they use, how sensible they are, or even the advantages and disadvantages of each test.
Type of substrate and signal
The substrate of an immunoassay is a key piece of the reaction, being the one that allows us to measure the results with ease and precision.
While an ELISA test utilizes chromogenic substrates like TMB or ABTS, which look to tint the sample to a greater or lesser degree to be able to measure the colour change; the CLIA assays utilize luminescent substrates like Luminol or acridinium ester, that glow after the reaction allowing to measure the light given by it.
Differences on sensibility
The difference between the grade of sensibility on both types of assays is stark. Despite both being able to detect fairly small quantities of the desired protein and are highly precise by their own merit, in this particular regard, CLIA tests are the clear winners.
Where an ELISA can detect proteins in a concentration of down to 500pg/mL, a CLIA test can detect them even in a concentration of 1pg/mL, making this technique an ultrasensitive one.
Advantages and disadvantages
Each one of these assays has a multitude of advantages and disadvantages that make them perfect for different kinds of experiments.
ELISA tests, for example, are fast and easy to perform in their most standard form, and many brands have on sale specialized kits that reduce the time needed to perform the protocol even further. They are also widely used in labs all over the world, making them a standard assay and a must-learn for every budding researcher.
Running against them, ELISA kits have a fixed period of time for the reading to happen, as it has to be done in the moments following the reaction enzyme-substrate, making it difficult to use them along flexible planning.
On the other hand, CLIA assays have a wider dynamic range than their counterparts, so they are considerably more precise. Their highly stable reagents and low depth ratio make them easy to automate and allow making the pertinent readings in a wide period of time after completing the assay.
However, CLIA assays make use of highly specialized equipment, like a luminescence microplate reader, making it a costly endeavour that is not widely accessible by the average laboratory.
Conclusion
To summarize, ELISA kits are a widely used and recognized method to identify the presence of an analyte in both a quantitative and qualitative way and have been praised as the gold standard on immunoassays.
CLIA tests, on the other hand, are the newer, shinier and more modern sibling to the ELISA kit. Boasting magnitudes of higher precision, it’s only held back by the need for expensive specialized equipment to make full use of the kit.
Both are useful in their own right and considering their characteristics before choosing one or the other for an experiment is the first step towards success.
