In biomedical contexts, a biomarker, or biological marker, is a measurable
indicator
Indicator may refer to:
Biology
* Environmental indicator of environmental health (pressures, conditions and responses)
* Ecological indicator of ecosystem health (ecological processes)
* Health indicator, which is used to describe the health o ...
of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal
biological process
Biological processes are those processes that are vital for an organism to live, and that shape its capacities for interacting with its environment. Biological processes are made of many chemical reactions or other events that are involved in the ...
es,
pathogenic
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
processes, or
pharmacologic
Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemic ...
responses to a
therapeutic intervention
An intervention is an orchestrated attempt by one or many people – usually family and friends – to get someone to seek professional help with a substance use disorder or some kind of traumatic event or crisis, or other serious prob ...
.
[ as cited in ] Biomarkers are used in many
scientific fields
The branches of science, also referred to as sciences, scientific fields or scientific disciplines, are commonly divided into three major groups:
*Formal sciences: the study of formal systems, such as those under the branches of logic and ma ...
.
Medicine
Biomarkers used in the medical field, are a part of a relatively new clinical toolset categorized by their clinical applications. The three main classes are molecular biomarkers, cellular biomarkers or imaging biomarkers. All three types of biomarkers have a clinical role in narrowing or guiding treatment decisions and follow a sub-categorization of being either predictive, prognostic, or diagnostic.
Predictive
Predictive molecular, cellular, or imaging biomarkers that pass validation can serve as a method of predicting clinical outcomes. Predictive biomarkers are used to help optimize ideal treatments, and often indicate the likelihood of benefiting from a specific therapy. For example, molecular biomarkers situated at the interface of pathology-specific molecular process architecture and drug mechanism of action promise capturing aspects allowing assessment of an individual treatment response. This offers a dual approach to both seeing trends in retrospective studies and using biomarkers to predict outcomes. For example, in metastatic colorectal cancer predictive biomarkers can serve as a way of evaluating and improving patient survival rates and in the individual case by case scenario, they can serve as a way of sparing patients from needless toxicity that arises from cancer treatment plans.
Common examples of predictive biomarkers are genes such as ER, PR and HER2/neu in breast cancer, BCR-ABL fusion protein in chronic myeloid leukaemia, c-KIT mutations in GIST tumours and EGFR1 mutations in NSCLC.
Diagnostic
Diagnostic biomarkers that meet a burden of proof can serve a role in narrowing down diagnosis. This can lead to diagnosis that are significantly more specific to individual patients.
![CardiacMarkerComparison](https://upload.wikimedia.org/wikipedia/commons/e/e0/CardiacMarkerComparison.JPG)
A biomarker can be a traceable substance that is introduced into an organism as a means to examine organ function or other aspects of health.
For example,
rubidium chloride
Rubidium chloride is the chemical compound with the formula RbCl. This alkali metal halide salt is composed of rubidium and chlorine, and finds diverse uses ranging from electrochemistry to molecular biology.
Structure
In its gas phase, RbCl is d ...
is used as a radioactive isotope to evaluate perfusion of heart muscle.
It can also be a substance whose detection indicates a particular disease state, for example, the presence of an
antibody
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
may indicate an
infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
.
More specifically, a biomarker indicates a change in expression or state of a protein that correlates with the risk or progression of a disease, or with the susceptibility of the disease to a given treatment.
One example of a commonly used biomarker in medicine is
prostate-specific antigen
Prostate-specific antigen (PSA), also known as gamma-seminoprotein or kallikrein-3 (KLK3), P-30 antigen, is a glycoprotein enzyme encoded in humans by the ''KLK3'' gene. PSA is a member of the kallikrein-related peptidase family and is secreted b ...
(PSA). This marker can be measured as a proxy of prostate size with rapid changes potentially indicating cancer. The most extreme case would be to detect mutant proteins as cancer specific biomarkers through
selected reaction monitoring
Selected reaction monitoring (SRM), also called Multiple reaction monitoring, (MRM), is a method used in tandem mass spectrometry in which an ion of a particular mass is selected in the first stage of a tandem mass spectrometer and an ion product ...
(SRM), since mutant proteins can only come from an existing tumor, thus providing ultimately the best specificity for medical purposes.
Another example is KRAS, an
oncogene
An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels. that encodes a
GTPase
GTPases are a large family of hydrolase enzymes that bind to the nucleotide guanosine triphosphate (GTP) and hydrolyze it to guanosine diphosphate (GDP). The GTP binding and hydrolysis takes place in the highly conserved P-loop "G domain", a pro ...
involved in several
signal transduction pathways
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellula ...
. Biomarkers for precision oncology are typically utilized in the molecular diagnostics of
chronic myeloid leukemia,
colon,
breast
The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues.
In females, it serves as the mammary gland, which produces and secret ...
, and
lung
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
cancer, and in
melanoma
Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, intestines, or eye ( ...
.
Digital
Digital biomarkers are a novel emerging field of biomarkers, mostly collected by smart
biosensors. So far, digital biomarkers have been focusing on monitoring vital parameters such as
accelerometer
An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is accele ...
data and
heartrate
Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and exc ...
but also
speech
Speech is a human vocal communication using language. Each language uses Phonetics, phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if ...
.
Novel non-invasive, molecular digital biomarkers are increasingly available recorded by e.g. on-skin sweat analysis (''internet-enabled Sudorology''), which can be seen as next-generation digital biomarkers. Digital biomarkers can be easily shared with the responsible physician, and novel diagnostics approaches can be developed using artificial intelligence.
Digital biomarkers are currently being used in conjugation with
artificial intelligence
Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech re ...
(A.I.) in order to recognize symptoms for
mild cognitive impairment
Mild cognitive impairment (MCI) is a neurocognitive disorder which involves cognitive impairments beyond those expected based on an individual's age and education but which are not significant enough to interfere with instrumental activities of ...
(MCI).
One major current use of digital biomarkers involves keeping track of regular brain activity. Specific neural indicators can be measured by devices to evaluate patients for any neuro abnormalities. The data collected can determine the patients disease probability or condition. While patients carryout everyday tasks (IADL), computers are using machine learning to observe and detect any deviation from normal behavior. These markers are used as signs or indicators of cognitive decline.
Prognostic
A prognostic biomarker provides information about the patients overall outcome, regardless of any treatment or therapeutic intervention.
One example of a prognostic biomarkers in clinical research, is the use of mutated ''PIK3CA'' in the study of metastatic breast cancer. As illustrated by the
graph
Graph may refer to:
Mathematics
*Graph (discrete mathematics), a structure made of vertices and edges
**Graph theory, the study of such graphs and their properties
*Graph (topology), a topological space resembling a graph in the sense of discre ...
, the mutation is prognostic since its presence in the patient endure the same outcome regardless of the treatment method used. Women who had the PIK3CA mutation before treatment, had the lowest average survival rate. The decline in the groups containing the mutant occurred quicker and in a much steeper decline. The independent nature of the prognostic factor allows researcher to study the disease or condition in its natural state. This makes it easier to observe these abnormal biological processes and speculate on how to correct them. Prognostic factors are often used in combination with predictive variables in therapeutics studies, to examine how effective different treatments are in curing specific diseases or cancer. As opposed to predictive biomarkers, prognostic do not rely on any explanatory variables, thus allowing for independent examination of the underlying disease or condition.
Nutrition and diet assessment
Nutritional biomarkers (biochemical markers of intake) are used to estimate dietary intake in
nutrition
Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient n ...
research, in particular
nutritional epidemiology
Nutritional epidemiology examines dietary and nutritional factors in relation to disease occurrence at a population level. Nutritional epidemiology is a relatively new field of medical research that studies the relationship between nutrition and ...
, but also in other disciplines such as
archaeology
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
where reliable dietary information are required.
A nutritional biomarker can be any specimen that reflects intake of dietary constituents and is sufficiently specific. Many biomarkers are derived from compounds found in foods, such as sugar or phytochemicals, or combinations thereof using a
metabolomics
Metabolomics is the scientific study of chemical processes involving metabolites, the small molecule substrates, intermediates, and products of cell metabolism. Specifically, metabolomics is the "systematic study of the unique chemical fingerprin ...
.
Another type of nutritional biomarkers, in particular common in
archaeology
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
, are
stable isotope ratio
The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...
s.
Research
Biomarkers for precision medicine are a part of a relatively new clinical toolset. In the case of metastatic colorectal cancer (mCRC) only two predictive biomarkers have so far been identified and implemented clinically.
In this case, the lack of data beyond retrospective studies and successful biomarker-driven approaches was suggested to be principal cause behind a need for novel biomarker studies within the medical field due to the severe attrition that accompanies clinical trials.
The field of biomarker research is also expanding to include a combinatorial approach to identifying biomarkers from multi-omic sources. Combining groups of biomarkers from various omic data allows for the possibility of developing panels that evaluate treatment response based on many biomarkers at a single time. One such area of expanding research in multi-omic biomarkers is mitochondrial DNA sequencing. Mutations in mitochondrial DNA have been shown to correlate to risk, progression, and treatment response of head and neck squamous cell carcinoma.
In this example, a relatively low cost sequencing pipeline was shown to be able to detect low frequency mutations within tumor-associated cells. This highlights the general snapshot capability of mitochondrial DNA-based biomarkers in capturing heterogeneity amongst individuals.
Regulatory validation for clinical use
The
Early Detection Research Network {{Short description, Cancer biomarker discovery project
The Early Detection Research Network (EDRN) is a collaboration led by the National Cancer Institute (NCI) focused on the discovery of cancer biomarkers. The effort, started in 2000, includes bo ...
(EDNR) compiled a list of seven criteria by which biomarkers can be assessed in order to streamline clinical validation.
Proof of concept
Previously used to identify the specific characteristics of the biomarker, this step is essential for doing an ''in situ'' validation of these benefits. The biologic rationale of a study must be assessed on a small scale before any large scale studies can occur.
Many candidates must be tested to select the most relevant ones.
Experimental validation
This step allows the development of the most adapted protocol for routine use of the biomarker. Simultaneously, it is possible to confirm the relevance of the protocol with various methods (histology, PCR, ELISA, ...) and to define strata based on the results.
Analytical performances validation
One of the most important steps, it serves to identify specific characteristics of the candidate biomarker before developing a routine test. Several parameters are considered including:
* sensitivity
* specificity
* robustness
* accuracy
* reproducibility
*practicality
*ethicality
Protocol standardization
This optimizes the validated protocol for routine use, including analysis of the critical points by scanning the entire procedure to identify and control the potential risks.
Ethical issues
In 1997 the National Institute of Health suggested a need for guidelines and legislation development that would regulate the ethical dimensions of biomarker studies.
Similar to the way that the Human Genome Project collaborated with the U.S. Office of Technology Assessment, biomarker susceptibility studies should collaborate to create ethical guidelines that can be implemented into the groundwork and proposal requirements of the studies.
Ensuring that all of the participants that are included each step of the project (i.e. planning, implementation, and the compilation of the results) are provided with the protection of ethical principles that are put in place prior to beginning the project. These ethical protections should not only protect the participants in the study, but also the non participants, researchers, sponsors, regulators, and all other persons or groups involved in the study.
Some ethical protections could include but are not limited to:
*
Informed consent
Informed consent is a principle in medical ethics and medical law, that a patient must have sufficient information and understanding before making decisions about their medical care. Pertinent information may include risks and benefits of treatme ...
of the participant
* Access to participation opportunities independent of race, socio-economic status, gender, sexuality, etc. (within the range allowed by the experimental protocol)
* Scientific integrity
*
Confidentiality of data (
anonymity
Anonymity describes situations where the acting person's identity is unknown. Some writers have argued that namelessness, though technically correct, does not capture what is more centrally at stake in contexts of anonymity. The important idea he ...
)
* Acknowledgement of conflict of interest in terms of funding and sponsorship by given sponsors
* Transparency and recognition of health and legal risks involved in participation
Cell biology
In
cell biology
Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and ...
, a
biomarker is a molecule that allows the detection and isolation of a particular cell type (for example, the protein
Oct-4
Oct-4 (octamer-binding transcription factor 4), also known as POU5F1 (POU domain, class 5, transcription factor 1), is a protein that in humans is encoded by the ''POU5F1'' gene. Oct-4 is a homeodomain transcription factor of the POU family. I ...
is used as a biomarker to identify
embryonic stem cells).
In
genetics
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...
, a biomarker (identified as
genetic marker A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can be ...
) is a
DNA sequence
DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...
that causes
disease
A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
or is associated with susceptibility to disease. They can be used to create genetic maps of whatever organism is being studied.
Applications in chemistry, geology and astrobiology
A biomarker can be any kind of
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
indicating the existence, past or present, of living organisms. In the fields of
geology
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
and
astrobiology
Astrobiology, and the related field of exobiology, is an interdisciplinary scientific field that studies the origins, early evolution, distribution, and future of life in the universe. Astrobiology is the multidisciplinary field that investig ...
, biomarkers, versus geomarkers, are also known as
biosignature
A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, or molecule – or phenomenon that provides scientific evidence of past or present life. Measurable attribute ...
s. The term biomarker is also used to describe biological involvement in the
generation of petroleum. Biomarkers were used in the geo-chemical investigation of an oil spill in the San Francisco Bay, California in 1988.
On April 22–23 around 400,000 gallons of
crude oil
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
was accidentally released into the
San Joaquin Valley
The San Joaquin Valley ( ; es, Valle de San Joaquín) is the area of the Central Valley of the U.S. state of California that lies south of the Sacramento–San Joaquin River Delta and is drained by the San Joaquin River. It comprises seven c ...
by a refinery and manufacturing complex of the
Shell Oil Company
Shell USA, Inc. (formerly Shell Oil Company, Inc.) is the United States-based wholly owned subsidiary of Shell plc, a UK-based transnational corporation " oil major" which is amongst the largest oil companies in the world. Approximately 18,000 ...
. The oil affected many surrounding areas. Samples of the crude oil were collected in the various regions where it had spread and compared to samples that were unreleased in an attempt to distinguish between the spilled oil and the petrogenic background present in the spill area.
Mass Spectra
A mass spectrum is a histogram plot of intensity vs. ''mass-to-charge ratio'' (''m/z'') in a chemical sample, usually acquired using an instrument called a ''mass spectrometer''. Not all mass spectra of a given substance are the same; for example ...
was performed to identify biomarkers and cyclic
aliphatic hydrocarbons
In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, o ...
within the samples. Variations in the concentration of constituents of the crude oil samples and sediments were found.
Ecotoxicology
Biomarkers are being used to identify the effects of water contamination on aquatic organisms.
Benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
macro-invertebrates reside in the
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
on the bottoms of streams, which is where many contaminants settle. These organisms have high exposure to the contamination, which makes them good study species when detecting pollutant concentrations and pollution impacts on an ecosystem. There are a variety of biomarkers within an aquatic organism that can be measured, depending on the contaminant or the response in question. There are also a variety of contaminants within water bodies. To analyze the impact of a pollutant on an organism, the biomarker must respond to a specific contaminant within a specific time frame or at a certain concentration. The biomarkers used to detect pollution in aquatic organisms can be enzymatic or non-enzymatic.
Rachel Carson
Rachel Louise Carson (May 27, 1907 – April 14, 1964) was an American marine biologist, writer, and conservationist whose influential book ''Silent Spring'' (1962) and other writings are credited with advancing the global environmental m ...
, the author of ''
Silent Spring
''Silent Spring'' is an environmental science book by Rachel Carson. Published on September 27, 1962, the book documented the environmental harm caused by the indiscriminate use of pesticides. Carson accused the chemical industry of spreading d ...
'', raised the issue of using organochlorine pesticides and discussed the possible negative effects that said pesticides have on living organisms. Her book raised ethical issues against chemical corporations that were controlling the general reception of the effect of pesticides on the environment, which pioneered the need for
ecotoxicological
Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem, and biosphere levels. Ecotoxicology is a multidisciplinary field, which integrates toxicology and ecology.
T ...
studies. Ecotoxicologial studies could be considered the precursors to biomarker studies.
Biomarkers are used to indicate an
exposure to or the effect of
xenobiotics
A xenobiotic is a chemical substance found within an organism that is not naturally produced or expected to be present within the organism. It can also cover substances that are present in much higher concentrations than are usual. Natural compo ...
which are present in the
environment
Environment most often refers to:
__NOTOC__
* Natural environment, all living and non-living things occurring naturally
* Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...
and in organisms. The biomarker may be an external substance itself (e.g.
asbestos
Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...
particles or
NNK
Nicotine-derived nitrosamine ketone (NNK) is one of the key tobacco-specific nitrosamines derived from nicotine. It plays an important role in carcinogenesis. The conversion of nicotine to NNK entails opening of the pyrrolidine ring.
Synthesis a ...
from tobacco), or a variant of the external substance processed by the body (a
metabolite
In biochemistry, a metabolite is an intermediate or end product of metabolism.
The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...
) that usually can be quantified.
History
The widespread use of the term "biomarker" dates back to as early as 1980. The manner in which the environment was monitored and studied near the end of the 1980s was still mainly reliant on the study of chemical substances that were considered dangerous or toxic when found in moderate concentrations in water, sediments, and aquatic organisms.
The methods used to identify these chemical compounds were chromatography, spectrophotometry, electrochemistry, and radiochemistry.
Although these methods were successful in elucidating the chemical makeup and concentrations present in the environment of the contaminants and the compounds in question, the tests did not provide data that was informative on the impact of a certain pollutant or chemical on a living organism or ecosystem. It was proposed that characterizing biomarkers could create a warning system to check in on the well being of a population or an ecosystem before a pollutant or compound could wreak havoc on the system. Now, due to the development of biomarker studies, biomarkers can be used and applied in the fields of human medicine and in the detection of diseases.
Definition
The term "biological marker" was introduced in 1950s.
* In 1987, biological markers were defined as “indicators signaling events in biological systems or samples” that could be classified into three categories: exposure, effect and susceptibility markers.
* In 1990, McCarthy and Shugart defined biomarkers as, “measurements at the molecular, biochemical, or cellular level in either wild populations from contaminated habitats or in organisms experimentally exposed to pollutants that indicate that the organism has been exposed to toxic chemicals, and the magnitude of the organism's response”.
* In 1994, Depledge defined a biomarker as, “a biochemical, cellular, physiological or behavioral change which can be measured in body tissues or fluids or at the level of the whole organism that reveals the exposure at/or the effects of one or more chemical pollutants.”
* In 1996, Van Gestel and Van Brummelen attempted to redefine biomarkers to unambiguously differentiate a biomarker from a bioindicator. According to Van Gestel and Van Brummelen, a biomarker by definition should be used only to describe sublethal biochemical changes resulting from individual exposure to xenobiotics.
* In 1998, the
National Institutes of Health
The National Institutes of Health, commonly referred to as NIH (with each letter pronounced individually), is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the late ...
Biomarkers Definitions Working Group defined a biomarker as "a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention."
* In 2000, De Lafontaine defined the term biomarker as a “biochemical and/or physiological change(s) in organisms exposed to contaminants, and thus represent initial responses to environmental perturbation and contamination".
Active biomonitoring
De Kock and Kramer developed the concept of active biomonitoring in 1994. Active biomonitoring is a comparison of the chemical/biological properties of a sample that has been relocated to a new environment that contains different conditions than its original environment.
See also
References
{{Authority control
Biological techniques and tools
Biology terminology
Biomarkers