Q&A with Eugenio Zabaleta, PhD
Medical Lab Management: What are the basic benefits of microarray technology in the clinical laboratory setting?
Eugenio Zabaleta: In today’s highly technical and integrated clinical laboratory, DNA microarray technology is becoming a powerful tool in the transformation of clinical diagnostics. This technique makes it possible to detect large amounts of polymorphisms in a single assay utilizing a DNA chip or biochip. Furthermore, DNA microarray assays can be performed in fully automated, multiplexing, molecular diagnostic platforms.
MLM: How can microarray testing benefit a laboratory in the community hospital setting?
Zabaleta: The benefits of microarray testing can be significant in the community setting. By way of example, when using DNA microarray technology, an instrument can detect 10 different variants or mutations on the enzyme responsible for Plavix (clopidogrel) metabolism. Depending on genetic make-up, some patients are able to experience the full value of the treatment (ie, they avoid stent occlusion and/or prevent stroke or acute myocardial infarction [AMI]), while others are not, and microarray testing can help in making this determination ahead of time. This testing type also can identify patients that are at higher risk of bleeding while on Plavix. Even in a mid-sized hospital system, there are always opportunities to practice state-of-the-art medicine, including DNA-guided testing (pharmacogenomics) to support interventional cardiology programs.
The most common uses of microarray tests in clinical practice (non-research) are for microbiology, inherited genetic conditions (diagnostic, carrier, and predictive testing), pharmacogenomics, and cancer mutation testing.
MLM: What infrastructure is needed to run microarray testing and how is it executed?
Zabaleta: First, there needs to be a clear separation between the pre- and post-nucleic acid amplification areas, as defined by good laboratory practices for molecular testing. Given the exquisite sensitivity of nucleic acid amplification techniques (NAAT)—such as polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP)—contamination of a DNA sample can ruin an entire experiment and jeopardize patient testing and care. Thus, in order to remain in compliance with established good practices for molecular testing, our molecular pathology laboratory is divided into two rooms—pre- and post-NAAT.
Second, the microarray-based test performed at OhioHealth MedCentral Hospitals consists of three steps:
Currently, the only microarray testing performed at OhioHealth MedCentral Hospitals is the CYP2C19 for Plavix response assessment.
MLM: Why was this test selected for use in your facility?
Zabaleta: In January 2009, the FDA published an early communication indicating its awareness that Plavix effectiveness was found to vary from person to person due to genetic differences (polymorphisms) and/or drug-to-drug interactions. Plavix is a prodrug that needs to be activated by the CYP2C19 liver enzyme to produce the desired anti-platelet activity. Around this same time, we (laboratory and interventional cardiology staff) became aware of an available microarray test that could determine CYP2C19 status. As interventional cardiology remains an area of strength among other valuable specialties at OhioHealth MedCentral, the joint laboratories department decided to implement this CYP2C19 test for Plavix response assessment as a joint venture between laboratory services and interventional cardiology in November 2009. Finally, in March 2010, the FDA added a boxed warning to the label for Plavix, further underscoring the need for this valuable testing type.
MLM: Were there any primary concerns when adding this test to the hospital’s service offerings?
Zabaleta: Among our chief concerns when bringing this testing type on board was enabling proper physician education. The CDC emphatically recommends laboratorians play a direct role in providing the specific information needed by physicians before decisions are made regarding test selection and ordering of molecular genetic testing. To fulfill this recommendation, the laboratory prepared an education document to provide a straightforward introduction to the science of pharmacogenetics, the specific microarray test for Plavix (clopidogrel), information about the clinical relevance of the test, the technical characteristics of our health system’s test (including limitations), a brief outline of how the test is resulted, and lastly, frequently asked questions about pharmacogenomics.
MLM: How has the lab worked with clinicians to ensure proper ordering of microarray testing?
Zabaleta: It was evident from the beginning that we needed to make the order process for this test intuitive to the physician to encourage proper utilization and avoid physician frustration. Within our CPOE system, the order for this test is called Plavix Genetic (CYP2C19) test. While CYP2C19 testing can be run to assess other drug responses, the interpretation of our test is specific to Plavix.
Furthermore, testing of this type requires a certain degree of training on the laboratory side in order to properly manage the process. In fact, CLIA requires personnel who perform high-complexity testing to have earned a doctoral, master’s, or bachelor’s degree in a chemical, physical, biological, or clinical laboratory science or medical technology from an accredited institution. Accordingly, we chose two laboratorians that met those requirements and had at least five years of clinical laboratory work experience to run our microarray. These two staff members also studied molecular diagnostic practicum in their academic institutions.
MLM: Is sample storage or resulting data storage an issue from a regulatory standpoint?
Zabaleta: This issue generally depends on where the laboratory is located. Some states require informed consent from patients for genetic testing, while others do not; currently, 27 states require informed consent of some kind. Independent of that, the hospital’s internal review board (IRB) may want to have administrative control over the samples and results storage, as is the case for us.
MLM: Under what conditions is the Plavix Genetic (CYP2C19) test properly ordered?
Zabaleta: The conditions for ordering the CYP2C19 test are the same as the clinical conditions for prescribing Plavix—acute coronary syndrome without ST-segment elevation (NSTEMI), ST elevation myocardial infarction (STEMI), stent placement, heart attack, heart-related chest pain, stroke, peripheral artery disease, higher risk of heart attack or stroke, or placement of an intra-coronary stent.
MLM: What type of patient specimen is necessary for this test and what is the testing methodology?
Zabaleta: In order to run this microarray test, the necessary specimen is whole blood drawn in a 4 mL lavender-top (EDTA) tube; no special patient preparation is required. Once the sample is in the lab, the molecular test to detect CYP2C19 allelic variants is performed using an automated blood DNA extraction technique followed by multiplex PCR amplification of DNA, fluorescent label incorporation using analyte specific primer extension (ASPE), hybridization of the ASPE primers to a microarray, and finally, signal detection and analysis of the data.
MLM: What is the data output and how does the lab use this information?
Zabaleta: The output provided by the detector is in relative fluorescence units (RFU). RFU is the numerical, digital readout for the fluorescent signal at the given spot of the microarray, which could be the mutant or the wild-type for each individual variant. In the case of the Plavix Genetic (CYP2C19) test, we are interrogating ten polymorphisms. According to the RFU of the wild-type and the RFU of the mutant, the software is going to make a determination for each individual polymorphism: wild-type, mutant, or heterozygous. The pathologist then will review the result to provide an analytical interpretation (the genotype of the patient) and clinical interpretation (the phenotype of the patient and the clinical significance of that phenotype).
MLM: How is this information then used by clinicians?
Zabaleta: The resulting information illustrates the fundamental value of microarray testing for CYP2C19. Instead of the typical trial and error, one-drug-fits-all, and one-dose-fits-all approaches, the genetic (CYP2C19) microarray test gives physicians the opportunity to individualize drug therapy for patients based on their genetic make-up. The patient’s genotype will be consistent with one of four different phenotypes: poor metabolizer (PM), intermediate metabolizer (IM), extensive metabolizer (EM), or ultra-rapid metabolizer (UM). According to the different phenotypes, the physician can consider increasing the dose, maintaining the standard dose, or choosing an alternative drug or alternative course of therapy. Decreasing the dose of Plavix is not possible because it comes in only one dose size (a 75-mg pill).
MLM: How does microarray testing for CYP2C19 exceed the value of your previous testing approach?
Zabaleta: Say, for example, a patient is admitted with acute coronary syndrome (NSTEMI) and extensive coronary artery disease with previous transient ischemic attack (TIA) or stroke (which is a contraindication for Effient [prasugrel], a Plavix alternative). The patient has two therapeutic options as stated by the interventional cardiologist; the first option is a catheter-based intervention involving the placement of drug-eluting stents. The second option is cardiac artery bypass grafting (CABG). Generally, the patient would prefer the first option, as it is a less invasive procedure. However, the interventional cardiologist would only agree to the stent placement procedure if the patient is responsive to Plavix therapy. In other words, the CYP2C19 Plavix test guides the physician in personalizing the right therapeutic option (stent vs CABG) for this patient. Thus, the timely performance of a CYP2C19 test is essential due to the acute nature of this type of disease. In this example, the patient turned out to be a Plavix responder (extensive metabolizer) and received two stents.
Before microarray testing became available in our hospital, the cardiologist would most likely have recommended the CABG method due to potential in-stent restenosis. Prior to the microarray, there was no other way to definitively forecast the patient’s response to Plavix therapy or his relative phenotype.
MLM: Do you expect your facility’s use of microarrays will continue to grow in the clinical setting?
Zabaleta: Yes, I think we are just at the beginning of the transformation of clinical diagnostics as far as the use of multiplex, lab-on-a-chip technology. At OhioHealth MedCentral Hospitals, we are always looking for opportunities to bolster the support of our physicians’ practices and advance our patients’ health care needs. Thus far, microarray testing has been a step in the right direction.
Eugenio H. Zabaleta, PhD, is a clinical chemist at OhioHealth MedCentral Mansfield Hospital. He also is a part-time lecturer in the Cleveland State University graduate clinical chemistry program. Dr. Zabaleta graduated from the Catholic University of Cordoba (Argentina) with a degree in biochemistry and received his PhD in chemistry from the University of Akron.
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