Rapid testing of infection and disease states: the faster the better

The word diagnosis is derived from the Greek words dia, which means ‘by or through’, and gnosis, which means ‘knowledge’. With respect to treating a patient, medical professionals have always sought to diagnose the disease or condition, thereby gaining knowledge to utilize in selecting a therapy that could cure the disease or alleviate the symptoms. Traditionally this was accomplished by questioning the patient about their symptoms and medical history, and conducting a physical exam of the patient. Based on their knowledge and previous experience, the medical professional could determine the disease or condition from which the patient was suffering, thus enabling them to recommend the best treatment strategy.

As science is advancing so are the therapies. Disease-specific therapies have and continue to be developed that are focused on curing the disease rather than simply alleviating the symptoms. This has elevated the importance of making the correct diagnosis, as a therapy will only benefit a patient if the correct one is utilized. Fortunately, scientific advances are also being made that give medical professionals tools that provide them with objective information which cannot be gained by physical examination. This increases their knowledge of the patient's condition, allowing a correct diagnosis to be made, resulting in the prescription of appropriate therapy and ultimately a cure.

The evolution of modern diagnostic tools can be traced back to the work of Robert Koch and Friedrich Loeffler in the 19th century. In studying bacteria postulated to cause infectious disease, Koch and Loeffler proposed criteria, later refined and published by Koch,¹ that would establish a link between a specific microbe and disease. Through this work, four postulates were proposed that became known as Koch's postulates. Briefly these were: (1) the microorganism must be found in all organisms suffering from the disease; (2) the microorganism must be isolated from a diseased organism and grown in pure culture; (3) the cultured microorganism should cause disease when introduced into a healthy organism; (4) the microorganism must be re-isolated from the inoculated, diseased experimental host and be confirmed as identical to the original specific causative agent.

As useful as the postulates were in identifying the specific microbe that caused a disease, it was not practical for medical professionals to fulfil these postulates prior to prescribing specific therapies. However, basic scientific work was initiated and completed that definitively linked specific diseases to specific microorganisms. This in turn allowed biochemists and microbiologists to devise tests that could be conducted on samples, i.e. throat swabs or bodily fluids, taken from the affected individual to identify the microbe present in the sample. Initial tests focused on morphological and biochemical analysis of the microorganism(s) present in the sample. While these tests were effective, these tests often required a week or more to obtain results since the requirement to culture the organism from the sample still remained. During this time, the disease continued to develop in the affected individual. Depending on the microorganism with which the individual was infected, this delay in diagnosis and treatment meant the difference between life and death to that individual, not to mention the likelihood that the disease could be spread to other healthy individuals. To provide a better standard of care, it was imperative that scientists focused their efforts on developing tests that would provide results more quickly. This could only be achieved by removing the necessity to culture microorganisms from a sample. These research efforts have led to the identification of biomarkers, substances whose detection is indicative of a particular disease state or infectious agent. Early biomarkers included antigens derived from virulent microorganisms, as well as the antibodies produced in response to a specific microorganism.

Biomarkers are not unique or limited to infectious disease. Biomarkers have also been identified that can provide information pertaining to non-infectious diseases such as cancer. For example, measurement of the levels of prostate-specific antigen (PSA), a protein normally present in small amounts in the blood of healthy men, taken together with patient history and the results of a physical examination, allows medical professionals to assess an individual's risk for developing prostate cancer (see Thompson and Ankerst for a review²).

Since their discovery, biomarkers were quickly utilized to develop tests to diagnose disease. Known as In-vitro Diagnostic Tests (IVD), these tests are relatively easy for individuals with basic training to perform. The development of IVD was a significant advance that allowed results to be available in hours to days rather than the weeks it took to complete classical testing. In turn, this has improved the standard of care and the prognosis for the patient. Early IVD included agglutination and immunodiffusion tests that capitalized on antigen–antibody interactions. These were followed by the development of Enzyme-linked Immunoassays (EIA) which have become ubiquitous in clinical laboratories around the globe.

However, science does not stand still. In fact, the pace of development has accelerated due to the multidisciplinary approach being taken to decrease the time needed to provide medical professionals with information about ailing as well as currently healthy patients. There are currently two research streams being pursued: the first is the identification and validation of new biomarkers, and the second is detection science. Both streams are bringing together scientists from multiple disciplines to develop highly sophisticated new IVD, with the goal of improving patient care. To detect disease earlier and more accurately as well as to monitor the efficacy of treatment, microbiologists, molecular biologists, pharmacologists and clinicians are working together to identify and subsequently validate the utility of new biomarkers that can be used to develop new IVD. Detection science is a field that brings together analytical chemists, physicists, biologists, and engineers with an interest in microfluidics and micro-/nano-electronics. Their goal is to develop new technologies for use as platforms in IVD. These technologies are capable of detecting ever lower concentrations of biomarkers faster and with less manipulation by laboratory professionals. Owing to the challenges such as decreased availability of trained technologists, shrinking budgets, and the need to provide test results more quickly, the field of detection science is also focused on developing point of care (POC) tests. The POC test is a subset of the IVD market which is seeking to bring IVD out of the traditional laboratory and closer to the patient, thereby improving the quality of care. These efforts have shown tremendous potential, specifically in the development of exquisitely sensitive biosensor technologies based on acoustic, optical, or electrochemical methods that do not require the use of labeled reagents to visualize biological interactions occurring on the surface of the biosensor. These label reagents are required in conventional technologies and make testing a cumbersome time-consuming process. The fact that biosensors eliminate the requirement for label reagents makes them easier to use and potentially allows for the measurement of biological interactions in real time.

While these two streams utilize different expertise and are seemingly divergent, they are actually quite complementary as the newly identified biomarkers often require integration with new detection technologies. This is because the use of existing technologies is often simply not feasible due to their limits of detection, incompatibility with the analyte/biomarker being detected, or their inability to perform multiplexed testing.

With the value of the market for IVD growing year over year, an enormous amount of resources is being poured into the two aforementioned development streams in the hopes of bringing to market new IVD that can provide medical professionals with more information to allow them to diagnose disease and to increase the profitability and viability of groups investing in the development efforts. While the future is bright for the patient, who will benefit from a higher standard of care provided by the new IVD, there are three significant hurdles: successful convergence of the two research areas, attainment of regulatory approvals to market the new products, and – oddly enough – acceptance of the technologies by laboratory technologists and medical professionals, which must be overcome before benefits can be realized by the patient.

As new biomarkers are discovered and new diagnostic platforms are developed they will converge and will need to be married together, so to speak, to produce a single diagnostic tool. As with any marriage, the initial union may yield what appears to be a very successful pairing; however, there is always a significant amount of work that needs to be done as two become one. This is primarily due to the incomplete understanding of the strengths and weaknesses of the converging technologies and the individuals developing them. For example, new biomarkers and biosensors are being identified and described each day. However, new IVD are not yet available due to the inability of biomarkers to be linked to the functional surfaces of biosensors in such a way that sensitive and specific signals are achieved. Fortunately, a handful of groups have identified this as the rate-limiting step and are working on surface chemistry solutions that will allow new technologies to emerge from the development laboratory.

As an example of the regulatory hurdles that new IVDs face, in the late 1990s there was tremendous pressure on the Food and Drug Administration (FDA) of the United States to approve additional tests to rapidly diagnose HIV-1. However, it was not until late 2002 and early 2003 that rapid tests that could detect antibodies to HIV-1 were approved. The unusual amount of time taken to approve the products was due in part to the lack of appropriate guidelines available to examine these new devices to ensure that they were safe and effective even though the technologies they employed were fairly simple. In addition, the first companies to obtain approval to sell these rapid HIV-1 tests were very young companies that had not previously manufactured, distributed, or obtained regulatory approval from the FDA for products that fell into the highest regulatory classification, Post Market Approval (PMA), for diagnostic tests. Today there are similar analogies in that most of the work being done in detection science and biomarker discovery is being done by relatively small companies or academic groups which have limited experience interfacing with global regulatory bodies. Fortunately, global regulators have identified the fact that new technologies and biomarkers are emerging and have released guidance documents that will help facilitate their approval, although some may argue that these guidance documents have not completely evolved. Ultimately, however, the onus is still upon the developers to ensure that the guidance documents are taken into consideration during development.

The final consideration in bringing new technologies to the market is that they are quite disruptive in the sense that they are very different from those currently used in clinical settings around the world. As people often resist change, there will be a significant amount of education that is required on the part of the manufacturer to demonstrate the advantages of the new technologies. More important to health care systems is the fact that a mechanism must also be in place for appropriate reimbursement when the new diagnostic tool is used. This can be a complicated process as these new technologies will likely cost more per test to purchase although the overall cost will be lower due to the decreased requirement of labor on the part of the laboratory technologist. Currently, health care systems use a series of reimbursement codes that stipulate how much money the care provider will receive for providing a specific result. Additionally, many of the codes specify a methodology to be used in providing the result, thus creating an additional level of complexity in successfully bringing new products to the market.

Improved diagnostics have benefited each and every one of us. Undoubtedly, each one of us or one of our family members has visited a physician who requested that a test be done; a test that ultimately provided the physician with the knowledge to make a diagnosis that led to prescription of a meaningful therapy. However, there is significant room for diagnostics to continue to evolve and the Darwinian phrase ‘survival of the fittest’ will again hold true. However, the definition of fitness may not. It may not be the most elegant or most sensitive technology – or the newest biomarker that ultimately makes it into our physician's tool kit. Instead, the diagnostic tools of the future will be the ones that result from the collective efforts of many groups of scientists, regulatory affairs professionals, and marketing and communications teams who work as one to launch new IVD.

References

1. R. Koch, J. Hyg. Inf., 1893, 14, 319–333.
2. I. M. Thompson and D. P. Ankerst, Can. Med. Assoc. J., 2007, 176(13), 1853–1858.

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