Clinical Chemistry Podcast

Previously, carrier screening has been used in at-risk and specific ethnic populations, or for a limited number of diseases. The broader screening approach, called expanded carrier screening, was endorsed in 2017 by the American College of Obstetricians and Gynecologists as an acceptable strategy for preconception and prenatal carrier screening. This is expected to have a significant clinical impact, as targeted screening approaches likely have missed a large number of affected pregnancies due to the limited conditions tested, the unknown ethnic ancestry of many individuals, and the fact that the majority of children born with a genetic disease have no family history of the condition. When provided with results that their pregnancy is at-risk for a severe condition, study show approximately 80% of such couples pursue alternative reproductive options. Given these consequences and the relative rarity of the included diseases, expanded carrier screening panels must have a high detection rate to correctly identify at-risk couples, and to minimize the residual risk when only one partner is tested positive. Though next generation sequencing has revolutionized genetic testing as a whole, advances in detecting copy number variants by next generation sequencing have been critical to improving the analytical quality of expanded carrier screening panels. An original research article appearing in the July 2018 issue of Clinical Chemistry describes these achievements while establishing the analytical validity of expanded carrier screening and quantifying how many pregnancies could be impacted by this approach in the general U.S. population.

Test standardization is a complex and multifaceted effort that's remained a major goal for laboratory medicine's professional societies, including the AACC and IFCC. Hemoglobin A1c is an example of a test that has undergone global standardization due to its worldwide importance in diabetes screening, diagnosis, and care. A key part of any standardization effort is aligning all manufacturers' methods to an accepted reference method. This was the main aim of the European Hemoglobin A1c trial devised by the IFCC's Committee on Education and Use of Biomarkers in Diabetes. The August 2018 issue of Clinical Chemistry includes an original research article that describes the European Hemoglobin A1c trial and its results.

Proper handling during the collection and processing of specimens is crucial for producing reliable results. These pre-analytical steps are highly vulnerable to the introduction of experimental bias and variance, which may drastically degrade specimen quality. Analytes are affected differently by uncontrolled variations in specimen collection, processing, and storage protocols. The August 2018 issue of Clinical Chemistry includes a Review article from the Precision Medicine and Pharmacometabolomics Task Group of the Metabolomics Society. The authors summarize the current variability among pre-analytical processing and biobanking procedures for metabolomics research and provide recommendations for best practices.

According to the World Health Organization, type 2 diabetes comprises the majority of the more than 400 million people with diabetes around the world. In efforts to better understand the disease, metabolomics measurements have identified tryptophan metabolites as potential biological mediators in the development of type 2 diabetes. The PREDIMED trial was a multi-center trial of Mediterranean-style diets where the primary prevention of cardiovascular events that also included type 2 diabetes as a secondary end point. An original research article published in the August 2018 issue of Clinical Chemistry studies whether tryptophan metabolites in PREDIMED participants were associated with development of type 2 diabetes and insulin resistance.

It was once thought that RNA only existed within cells. However, recent discoveries show that RNA is exported from cells and may be functional in cell to cell communication. This extracellular RNA can be abundant and stable and is found in bodily fluids such as saliva. Saliva has long been of interest for biomarker discovery and development, given its noninvasiveness and relative ease of collection. Despite these advantages, use of saliva for understanding more about extracellular RNA and its role in human biology and disease through RNA sequencing has some challenges. The high bacterial content and low abundance of extracellular RNA in saliva mean that optimization of RNA library construction and isolation protocols are critical to the success of these RNA sequencing experiments. An original research article in the July 2018 issue of Clinical Chemistry compares different RNA isolation methods and library construction kits for long and small RNA sequencing of salivary extracellular RNA. The authors described which protocols provide the best RNA yield and detection by next generation sequencing.

Liquid biopsy methods are an exciting area in cancer screening, diagnosis, and management. These methods are aimed at measuring genomic signatures of tumor cells in the blood. They rely on detection of circulating tumor cells, tumor-derived extracellular vesicles, or exosomes, or cell-free circulating DNA. Liquid biopsy methods have been proposed to compliment, enhance or perhaps even replace tissue biopsy in some scenarios. Liquid biopsy methods are an exciting area in cancer screening, diagnosis, and management. These methods are aimed at measuring genomic signatures of tumor cells in the blood. They rely on detection of circulating tumor cells, tumor-derived extracellular vesicles, or exosomes, or cell-free circulating DNA. Liquid biopsy methods have been proposed to compliment, enhance or perhaps even replace tissue biopsy in some scenarios. Beyond the minimal invasiveness, performing liquid biopsy may overcome some other weaknesses of tissue biopsy that are related to a single site's inability to capture intratumor heterogeneity or be representative of all the changes within the tumor. All three approaches to detect a tumor's genetic material have been applied for therapy stratification and monitoring in breast cancer. However, knowledge about the differences between these methods in the same patient cohort is limited. An original article in the July 2018 issue of Clinical Chemistry compared messenger RNA profiles of circulating tumor cells and extracellular vesicles in patients with metastatic breast cancer to estimate the utility of each in therapy management.

Laboratory testing is a key component of models of care for all types of lipid disorders. New therapies demand accuracy of dyslipidemia testing at very low LDL cholesterol concentration ranges. Inaccurate results lead to incorrect diagnosis and therapeutic management, both of which are costly to society and harmful to patients. To address these key issues of lipoprotein and apolipoprotein markers and reach consensus on contemporary lipid testing, a multidisciplinary panel was established by the European Federation of Clinical Chemistry and Laboratory Medicine and the European Atherosclerosis Society. The July 2018 issue of Clinical Chemistry includes a special report from this joint consensus initiative. It provides recommendations for improving the use of the lipid profile to assess cardiovascular disease risk conferred by atherogenic lipoproteins.

Cardiac troponins are recognized as the primary biomarkers used in the diagnosis of acute myocardial infarction. These are commonly detected by immunoassays, which offer the wide availability and rapid results needed in clinical care scenarios to rule out myocardial infarction. However, immunodetection methods can be limited when there is degradation of the target analyte, as is the case with cardiac troponin I. Early studies suggested that the central region, located between amino acid residues 30 and 110, was the most stable part of the molecule. This was a driver for the majority of current diagnostic systems to utilize antibodies with epitopes located within the central region. A down side to this approach is that auto antibodies also bind to this region, potentially causing interference and erroneous results. As more recent studies have identified additional cardiac troponin I proteolytic fragments, it is important to understand their composition and prevalence in the blood of patients with acute myocardial infarction. Furthermore, there is a need to evaluate whether monoclonal antibodies specific to the regions beyond the central section of the molecule can be used to develop cardiac troponin I assays with improved performance over those currently available. An original article appearing in the July 2018 issue of Clinical Chemistry describes a study investigating these concepts.

The June 2018 issue of Clinical Chemistry published a Perspective article titled, "Clinical Utility of Transcriptome Sequencing: Towards a Better Diagnosis for Mendelian Disorders." In it, the authors Drs. Sumant Chakravorty and Madhuri Hegde discussed the impact of findings by Cummings and colleagues, who have shown for the first time in 2017 the clinical utility of next generation sequencing based transcriptome sequencing to increase molecular diagnostic yield by sequencing RNA.

Dementia is a devastating disease with a huge global impact. Today, over 46 million people live with dementia worldwide. It is possible that promising treatments for Alzheimer's disease have failed thus far because treatment was started at a late stage of the disease process. So, early treatment could be beneficial, but how do you recognize a patient with Alzheimer's disease if he or she does not present with clinical symptoms? This is a key question, and presents an enormous opportunity for laboratory test based on biological markers of ongoing brain pathology. One example is measurement of neurogranin, a protein in cerebrospinal fluid that correlates with cognitive decline and is a potential novel biomarker for Alzheimer's disease dementia. There are multiple antibody-based neurogranin assays, which all target different segments of the protein. An original article in the June 2018 issue of Clinical Chemistry compared the analytical and the diagnostic performance of three commonly used neurogranin assays on the same cohort of patients.

Tuberculosis is a prevalent and potentially deadly infectious disease with a worldwide incidence of more than 10 million new cases each year, and in 2015 alone, 1.4 million deaths were attributed to TB. Much of the world relies on microbiologic techniques to detect tuberculosis including smear microscopy and mycobacterial culture which has a very long sample to answer timeframe. Both methods also have low clinical sensitivity for paucibacillary TB cases which account for more than 60% of new TB cases each year in emerging endemic areas such as China. PCR-based methods are faster but also have limitations. In the May 2018 issue of Clinical Chemistry, Dr. Tony Hu and his colleagues described a new peptide-based approach to detecting TB that overcomes those issues by using antibody conjugated nanoparticles, or nanodiscs, to bind specific peptides present in digested serum samples from cases of tuberculosis. These are then detected by benchtop matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, or MALDI-TOF MS.

Metastatic or recurrent cancers are a common cause of death among cancer patients. Genomic investigations of cancer over the past 10 years have led to tremendous advancement in the understanding of the underlying biology and in the development of targeted treatment options. Much of the discovery has been focused on primary treatment-naive cancers, since biological specimens for genomic analysis are more abundant in these cases that are available from patients with metastatic cancers. The lack of specimens has provided a significant obstacle in the genomic study of metastatic cancers. Therefore, a recent study by Dr. Dan Robinson and colleagues reported in the journal Nature has raised excitement. The investigators performed integrative analysis of DNA and RNA data for 500 metastatic lesions obtained from cancer patients with over 30 different primary cancer diagnoses to derive several types of molecular characterizations. Though further studies are needed, applying these approaches to individual patients in the clinical setting of metastasis may lead to more precisely tailored therapeutic treatments with higher effectiveness. The May 2018 issue of Clinical Chemistry includes an expert commentary on this noteworthy study.

Surgery is a common form of treatment in patients with solid tumors. Depending on the cancer, surgery may be used to remove cancer that is contained within a specific area, to debulk a tumor, or to ease symptoms caused by a tumor. In each case, it is critical to distinguish cancerous from noncancerous tissue during the operation. Today, pathologists perform rapid microscopic investigations of biopsied tissue and make the diagnosis. In the future, this may be conducted using mass spectrometry based measurements. Ambient ionization mass spectrometry methods make localized molecular level chemical analysis of tissue samples possible at atmospheric pressure and without prior sample purification and pre-treatment. Over the past decades, scientific advances have extended the role of these methods from the research laboratory to the operating room. The April 2018 issue of Clinical Chemistry includes a commentary on the different technologies and their potential in cancer diagnosis.

Cardiac troponin measured with newer generations of analytically highly sensitive assays have been investigated in accelerated discharge protocols on the assumption that they have an improved ability to detect and quantify cardiomyocyte injury more quickly than previous generation's assays. In the May 2018 issue of Clinical Chemistry, Dr. Jaimi Greenslade from the Royal Brisbane and Women's Hospital in Herston, Australia, and her colleagues investigated a high sensitivity cardiac troponin I assay to see if a single test threshold can safely rule out acute MI.

Amniocentesis is a common procedure usually performed to collect cells from the fetus to allow testing for abnormal chromosomes. Cells from the amniotic fluid are collected through centrifugation, cultured, and after about two weeks, analyzed by fluorescent in situ hybridization, or FISH, or with a microarray to detect abnormal chromosome copy number changes or large chromosomal structural rearrangements. These tests have become the gold standard for detecting Down Syndrome and several other serious birth defects because they have a low false positive rate. However, they are unable to detect the majority of birth defects.Amniocentesis is a common procedure usually performed to collect cells from the fetus to allow testing for abnormal chromosomes. Cells from the amniotic fluid are collected through centrifugation, cultured, and after about two weeks, analyzed by fluorescent in situ hybridization, or FISH, or with a microarray to detect abnormal chromosome copy number changes or large chromosomal structural rearrangements. These tests have become the gold standard for detecting Down Syndrome and several other serious birth defects because they have a low false positive rate. However, they are unable to detect the majority of birth defects. In the April 2018 issue of Clinical Chemistry, a paper demonstrated the feasibility of generating an accurate whole genome sequence of a fetus from either the cellular or cell-free DNA of an amniotic sample.

High-density lipoprotein, or HDL, cholesterol is often referred to as the "good" cholesterol due to its involvement in transport of cholesterol from peripheral tissues back to the liver during reverse cholesterol transport. However, some studies have demonstrated that the size and composition of HTL particles may influence the mechanism and capacity for this cholesterol efflux and other possible protective activities. So, some researchers believe that measurement of HTL particles, size, and composition may provide an indication of HTL protective activity. The March 2018 issue of Clinical Chemistry published a report comparing five different procedures for HDL particle measurement. In the same issue an editorial by Dr. Jeffrey Meeusen appeared titled "Comparing Measures of HDL: On the Right Path with the Wrong Map."

Data on biological variation can be used in many ways, most notably for the diagnosis and monitoring of disease and also for setting analytical performance specifications. In 2014, after the first strategic conference of the European Federation of Clinical Chemistry and Laboratory Medicine, a task force was established to develop criteria for evaluation of the literature on biological variation. A report from this group appears in the March 2018 issue of Clinical Chemistry.