Vol. 23 • Issue 8 • Page 16
Multiplex Testing
Clinical testing is becoming more targeted while simultaneously providing additional information for the healthcare professionals utilizing the equipment. Nowhere is this more evident than in the multiplex testing options available in laboratories. In the case of serology, the ability to test for multiple antigens and antibodies from a single sample could be a game-changer in the way patients are both diagnosed and subsequently treated. In a recent interview with ADVANCE, representatives from Bio-Rad Laboratories Inc. provided insight into multiplex technology and the future of laboratory screening.
Two immunoglobulins are frequently measured in blood screening for current or past infections, IgM and IgG. The presence of IgM antibodies can indicate an acute or recent infection. Typically, a positive IgM result would indicate to clinicians that a patient has had an infection within 3 months of the test or currently has an active infection. While the patient may respond to antibiotics and be cured, the IgM antibodies can still be detected for 3 months or longer. Due to genetic variance between patients or a compromised immune system, however, some patients do not have IgM responses.
“If IgM antibodies to a specific infectious agent are present, it is likely that the infection has occurred within the last 3 months or is possibly active now,” said Steven Binder, senior director of technology development at Bio-Rad Laboratories’ clinical diagnostics group.
On the other hand, IgG responses are usually more permanent. As IgG antibodies will persist as the body’s way of protecting itself against a future infection like a vaccination, a positive result simply tells clinicians that there has been an infection. With that said, Binder pointed out that IgG responses can also be used to indicate an active infection in certain cases. For example, untreated syphilis may not be detected for years. So, at some point, the IgG antibody may be the only indicator of this infection.
“For most infectious diseases, IgG will continuously be present after the initial infection,” continued Binder. “So when the laboratories look for IgG, they’re looking for evidence that there was, at some point, an infection, not necessarily current.”
One of the main benefits of multiplex testing is the ability to diagnose for possible infections transmitted from a mother to her child. Toxoplasmosis, rubella, cytomegalovirus, and Herpes simplex virus type 1 and 2 (ToRCH) tests are frequently grouped and ordered together. Because multiplex testing allows laboratory professionals to test for multiple analytes from the same sample, there is no need to run separate tests for multiple infections. Additionally, a healthcare facility must consider the health of its staff by determining the risks for those previously unexposed to certain infections. In this case, multiplexing can also be utilized in an immune testing capacity.
“Using multiplexing, we help hospitals determine if their medical staff is likely to acquire childhood diseases like mumps or measles, which they can easily acquire from patients if they haven’t been previously exposed,” commented Binder. “So, in that situation, a positive IgG result is considered evidence of immunity due to prior exposure or vaccination.”
Besides the capability of providing multiple results using a single sample, multiplex technology also allows laboratories to minimize space requirement by consolidating multiplex tests on a single platform. In addition, it offers significant time and labor saving, as well as reducing the cost for testing reagents and supplies. While multiplexing can also provide clinicians with additional information on testing results, there are limitations. Multiplex assays provide targeted analysis, which means the test can only provide information on those specific analytes that are “predefined” in the assay.
“It is a targeted analysis,” explained Paulina Leung-Lee, a senior product manager at Bio-Rad Laboratories. “You have to know what you’re looking for and, also, you have to understand how to interpret the results.”
Looking toward the future, an exciting area of multiplex testing is the potential for more informative HIV testing. Although no automated options are available in the United States yet, multiplexed HIV results are used in confirmatory testing and are being developed for screening as well. Binder noted the prospect of possibly using the technology for tumor analysis, especially considering the limited options available for screening. In the meantime, multiplexing stands to change the way clinical labs produce and interpret results.
Michael Jones is on staff at ADVANCE.
Sidebar: Benefits of Multiplex Methods
The new array methods share a number of characteristics of traditional multiplex methods
A single calibrator or calibrator set can be used to establish quantitative results for multiple analytes, rather than separate calibrators for each analyte. In the same way, a single control or control set can be used to monitor performance.
Because only one determination is performed, the sample volume requirement is reduced. This is especially valuable for pediatric samples or when a large number of analytes must be measured.
Internal standards may be used to monitor the quality of each patient result rather than determining quality of an entire run or series of results.
When diagnostic results must be considered together to provide an interpretation, all multiplex test results are in one place and were determined at exactly the same time, eliminating the need for the diagnostician to be concerned that something wasn’t ordered or that there was insufficient sample to complete the required testing.
– Steven Binder and Ginger Weeden, MLS(ASCP)CM
