When you go to a doctor, they will usually offer you a blood test. The results of this test can be important in many situations, such as determining if you have HIV or are at risk for the disease. But what is the difference between an Elisa test and Western blot? Below we discuss some key differences between these two tests that are both used for screening for HIV infection:
A negative ELISA result means that you do not have enough antibodies bound to the antigen in question for us to detect them at this point. In many cases, this indicates that you do not have active infection. A negative result may also mean that you were exposed recently and haven't had time yet to develop antibodies against your new pathogen—this could indicate early stages of infection and prompt follow-up testing with Western Blots which would allow us to determine if there really was an infection or whether it was just a false positive from a previous exposure.
The Western blot is a highly specific method for detecting antibodies to HIV-1 and HIV-2. It is particularly useful in patients who have had a negative ELISA, but whose seronegative status has not been confirmed by other testing methods (such as PCR).
The Western blot technique is more sensitive than the ELISA test, but it requires specialized equipment and trained personnel to perform. Furthermore, it's more expensive than the ELISA test.
Elisa is an immunoassay, which means that when you run the test, a series of antibodies will bind to different proteins and create a band profile. Each protein is detected by its own specific antibody that has been labeled with a fluorescent dye. The technician will then interpret this band profile and compare it with known positive or negative controls.
The blots are visualized using an instrument called an imager, which takes pictures of each lane (or group of lanes) in the gel at one time. The images are then loaded into a computer program that allows you to count how many bands appear for each lane, as well as any imperfections in your sample (called background noise).
Typically, Elisa tests give only one or two results, positive or negative. Western blot gives three possible results; indeterminate (uncertain), positive, or negative.
If your sample is determined to be negative by the Elisa test, it will have no visible bands whatsoever on your blot. If your sample is determined to be positive by the Elisa test, there may be visible bands at these locations on your blot:
The number of visible bands you see depends on how many copies of this particular POI are present in your sample and how sensitive your assay is. For example: If someone has 15 copies of HIV proteins circulating in their blood stream but only 10% are detectable by our assay because we used a very low dilution factor during testing then only 1 band might appear under normal circumstances while if we used higher dilutions then 2-3 additional bands would also appear.
The first difference between the Elisa test and the Western blot is that the western blot gives you a visual result. You can see which proteins are present or absent in your sample, whereas with an ELISA test you get only numerical results.
Another main difference is that the western blot takes longer than an ELISA test -- several days versus several hours. This makes it less practical for most people who just want to know whether they’re infected or not (although it can be useful if you want more information about your infection).
The third major difference between these two methods is their sensitivity: The results from a Western blot are usually more sensitive than those obtained by means of an ELISA test -- so if there are any antibodies present in your blood sample, they will be detected by this method but not necessarily by other tests such as RASTs (radioimmunoassay) or IFA (indirect fluorescent antibody assay).
It is important to understand what type of test you are taking and why for diseases such as HIV. The ELISA test is more sensitive than the Western blot, meaning it will detect lower levels of antibodies. For example, if someone has been infected with HIV but the virus has not yet reached their bloodstream, they may have enough antibodies in their body to be detected by an ELISA test but not a Western blot.
The time frame for results varies depending on which type of test you take. The ELISA can provide an answer in one week while the WB might take up to three weeks or longer depending on what kind of lab you use and when your sample was received by them.
With these facts in mind, you can see that it is important to understand what type of test you are taking and why for diseases such as HIV. The Elisa test is a screening test for HIV infection, which means that it can give only one or two results: positive or negative. If the result is positive then we need to confirm this with another test called Western Blot because it has a higher sensitivity than ELISA (detects antibodies against HIV antigens). The Western Blot method looks at specific bands on the blot which indicate whether there are antibodies present or not; therefore, giving three possible results: indeterminate (uncertain), positive or negative