Appendix: Biomedical Definitions

Association, causation

An association is a relationship, or correlation. A positive association means as one goes up, so does the other. A negative association means as one goes up, the other goes down.

Causation is when an event or variable is shown to cause a specific outcome. Whether a study shows association or causation depends on the study design.

Acquire, develop

Patients acquire  infectious diseases; they do not develop infectious diseases. Noncommunicable diseases, however, develop in patients — like Alzheimer’s disease or diabetes.


Biomarkers, or biological markers, are biological substances, characteristics, or images that provide an indication of the biological state of an organism. Biomarkers can include physiological indicators (e.g., blood pressure), molecular markers, (e.g., liver enzymes, prostate-specific antigen), and imaging biomarkers (e.g., those derived from magnetic resonance imaging and angiography).

An NIH working group defined a biomarker as “a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacological responses to therapeutic intervention.”


Biopsy is the procedure of removing and examining tissue, cells, or fluids from the body. Do not use it as a verb. Observations are made on the biopsy specimen, not on the biopsy itself.


Cohort is not plain language. When writing for the public, define the term first or consider referring to the cohort through alternative means, e.g., Researchers found that Asian American women aged 30-50 have…

Communicable vs. noncommunicable

Communicable diseases can be spread. They are also referred to as transmissible.

Noncommunicable diseases are not transmitted through contact with an infected or afflicted person. They are, instead, caused by various genetic, physiological, environmental, and behavioral factors. The World Health Organization identifies four main types of noncommunicable diseases: cancer, cardiovascular diseases (e.g., heart attacks), chronic respiratory diseases (e.g., asthma), and diabetes.


Comorbidity is the co-occurrence of more than one disorder, disease, or condition in the same individual. The article Defining Comorbidity: Implications for Understanding Health and Health Services explains that the term and its related constructs, such as multimorbidity, morbidity burden, and patient complexity, need more precise definitions.

While this term is still used broadly, it is considered stigmatizing by some in the HIV community. The preferred language is complication, when applicable.

Complementary or alternative medicine

Complementary and alternative approaches are those with origins outside of mainstream or Western medicine. A nonmainstream health practice used together with conventional medicine is complementary. A nonmainstream health practice used instead of conventional medicine is alternative.

Don’t use alternative if the substitution is something conventional doctors would approve of (for example, if a patient is no longer taking ibuprofen for back pain now that he’s practicing yoga regularly). When an approach is used for wellness, it’s okay to use complementary even though the person may not be receiving conventional care (because none is needed).

Complementary and alternative approaches include products, such as herbs or dietary supplements, as well as hands-on practices (e.g., acupuncture or spinal manipulation), other psychological or physical approaches (e.g., meditation, hypnosis, yoga), and even entire systems of care (such as Ayurvedic medicine or naturopathy). Otheracceptable terms for approaches include health, medicine, and practices. Avoid using the term medicine when referring just to products. See also integrative health.

Comprise, compose

The whole comprises the parts and the parts compose the whole. Comprise means contain, consist of, or made up of. For example, the FMR1 gene comprises 18 exons interspersed over ~40,000 base pairs of sequence, or, NIH comprises 27 Institutes and Centers.

Compose means “to be or constitute a part or element of the whole.” For example, 18 exons interspersed over ~40,000 base pairs of sequence compose the FMR1 gene.

Comprise and compose have similar meanings, but don’t write comprised of. Use composed of or constitute instead.


Condition indicates a state of health, whether well or ill. A condition conferring illness might further be classified as a disease or disorder, however, condition might be used in place of disease or disorder when a non-disease-specific term is indicated.

For example: Urinary retention is a condition in which you are unable to empty all the urine from your bladder. Urinary retention is not a disease, but a condition that may be related to other health problems, such as prostate problems in men or a prolapsed bladder in women.

Congenital vs. heritable

Congenital and heritable are often confused. Congenital describes conditions or traits that are acquired, either at birth or during development in the uterus. Most often, congenital indicates that some factor, such as a drug, chemical, infection, or injury has upset the careful timing and balance of the developmental process in a way that adversely affects the fetus.

For example: A baby born with spina bifida most likely cannot pass this congenital condition on to future generations.

Heritable characteristics or conditions are intrinsic to the genetic makeup of an individual and are capable of being passed from one generation to the next.

For example: A baby born with a heritable disease, such as hemophilia, can pass the disease on to future generations.

Contagious vs. infectious

Contagious refers to a disease that can be transmitted from one living being to another through direct contact (as with measles) or indirect contact (as with cholera). The agent responsible for the contagious character of a disease is described as infectious, the usual culprits being microorganisms, such as viruses and bacteria, or macroorganisms, such as fungi or parasitic worms.

COVID-19 is both contagious (easily passing from person to person) and infectious (the infectious agent is the SARS-CoV-2 virus). Alternatively, the parasite that causes malaria is infectious, but malaria is not contagious.

Contraception, contraceptive

Contraception is the practice of preventing pregnancy. Contraceptive is the method used
for contraception.


Patients are not critical, but their status or condition is.


Conditions, diseases, and disorders are diagnosed, not patients. Diagnosis is the process of identifying a disease, condition, or injury from its signs and symptoms. A health history, physical exam, and tests, such as blood tests, imaging tests, and biopsies, may be used to help make a diagnosis.

Die of, die from, die with

People die of, not from, a condition or disease. People can also die with a disease that is not the immediate cause of death.


Disease is often used in a general sense when referring to conditions that affect a physical system (e.g., cardiovascular disease) or a part of the body (e.g., diseases of the eye). The term also may be used in specific senses, such as Alzheimer’s disease.


A disorder is a disturbance of normal functioning of the mind or body. Disorders may be caused by genetic factors, disease, or trauma. For example, a disorder resulting from cardiovascular disease is an arrhythmia or irregular heartbeat. An arrhythmia is not a disease itself; it’s an abnormal heartbeat that occurs because of cardiovascular disease. In mental health, the terms mental disorder, mental illness, and psychiatric disorder are used interchangeably.

DNA or genome sequencing

Specify DNA (or genome) sequencing and DNA (or genome) sequence; do not simply write sequencing or sequence.

When referring to sequencing, use genome sequencing or genome sequencing data, not genomic. See also: Genome.

Dose vs. dosage

Dose is amount taken at one time. Dosage is the amount to be taken over time.

Endemic, epidemic, pandemic

AP Stylebook: Endemic, epidemic, pandemic
Endemic describes a disease (or characteristic) that is restricted to a particular region, such as cholera and plague in parts of Asia. A disease is endemic in an area; the area is not endemic. Sometimes, endemic is used to described when a disease is still among us but relatively under control, like influenza, e.g., “Although we may be out of the urgent pandemic phase, we’re not quite ready to call COVID-19 endemic…”

Epidemic refers to a disease that involves many more people than usual in a particular community or a disease that spreads into regions in which it does not normally occur.

Pandemic is the outbreak of a disease occurring over a wide geographic area and affecting a large number of people.

Gene and protein names

Gene names should be italicized, whereas related proteins should not be italicized (e.g., RAS gene and RAS protein). Human and other primate gene and protein names are given in capital letters; mouse and rat genes and proteins are presented with an initial capital (e.g., human BRCA1 gene but mouse Brca1 gene). Refer to Chicago Manual of Style 8.132: Genes.

Also reference the Guidelines for Human Gene Nomenclature based on the HUGO Gene Nomenclature Committee.

Genetics and genomics

Genetics is a term that refers to the study of genes and their roles in inheritance—the way that certain traits or conditions are passed down from one generation to another. Genetics involves scientific studies of genes and their effects.

Genomics is the study of all a person's genes (the genome), including interactions of those genes with each other and with the person's environment.

The main difference between genomics and genetics is that genetics scrutinizes the functioning and composition of a single gene, and genomics addresses all genes and their inter-relationships to identify their combined influence on the growth and development of the organism.


A genome is the complete set of DNA (genetic material) in an organism. In people, almost every cell in the body contains a complete copy of the genome. A genome contains all the information needed for an individual to develop and function.

Genus and species names

Spell out and italicize genus and species names at first use and use an initial capital for the genus name (e.g., Escherichia coli or Homo sapiens). Abbreviate the genus or species name using the first letter and a period with subsequent uses (e.g., E. coli, H. sapiens). Refer to Chicago Manual of Style 8.120: Genus and specific epithet. Species should ideally be identified by full common name at first mention. For example, fruit fly (Drosophila melanogaster), rhesus monkey (Macaca mulatta).

Germ, microbe, microorganism, pathogen

Germ and microbe are nontechnical terms describing a living organism, especially one invisible to the naked eye, that can cause disease. Generally, use a specific term — virus, bacteria, or parasite — instead of germ. If writing for a publication aimed at people with lower reading levels, the term germ is acceptable.

A pathogen is an agent that causes diseases, especially a bacterium, fungus, or other microorganism.

Microorganism is a general term that describes all one-celled microscopic organisms, both disease-causing and benign.

Incidence, prevalence

Incidence refers to the number of newly diagnosed cases during a specific time. Prevalence refers to the number of new and pre-existing cases for people alive on a certain date.


An incurable disease, disorder, or condition is one that does not currently have a cure. Incurable is not synonymous with terminal or fatal. While many incurable diseases are terminal, there are also many incurable conditions that a person can live with all their life. Medical conditions such as diabetes or asthma cannot be cured, but they can be managed.

Influenza, avian flu, swine flu, seasonal flu, pandemic flu

See the Web Style Guide | for explanations.

Integrative health

Use integrative when writing about incorporating complementary approaches into mainstream health care. Note: use integrative, not integrated.

Integrative medicine refers to health services, a philosophy that emphasizes treating the whole person, rather than one organ system or specialty, and an interest in well-coordinated care between different providers and institutions. The integrative approach seeks to address aspects of illness and health beyond the biological, such as mental, emotional, functional, spiritual, social, and community aspects as well.

See also complementary or alternative medicine.

Maternal morbidity

Maternal morbidity describes any short- or long-term health problems that result from being pregnant and giving birth. Use the term maternal health as a more positive term for general purposes and limit maternal morbidity for specific problems.

Maternal mortality

Maternal mortality refers to the death resulting from complications of pregnancy or childbirth that occur during the pregnancy or within six weeks after birth.

For more associated terms, please see the Eunice Kennedy Shriver National Institute of Child Health and Human Development’s page on Maternal Morbidity and Mortality.


Morbidity means both “the relative incidence of disease” and “the condition of being diseased.” Change morbidity to illness, disease, or condition when writing for lay audiences.

Mortality, mortality rate, fatality

Mortality means “the number of deaths per standard unit of population per unit of time.” Change mortality to death for lay audiences.

Mortality rate means “the number of deaths per number of persons at risk,” as in infant mortality rate (the ratio of numbers of infant deaths during a calendar year to the total number of live births during that year). Distinguish mortality from fatality.

Fatality is a death resulting from a disaster.


The adjectives nonpharmacologic and nonpharmacological refer to therapy that does not involve drugs, e.g., nonpharmacologic management of pain. It is written without a hyphen.

Nonpharmacologic and nonpharmacological are interchangeable. Similar to economic and economical, or neurologic and neurological, they may have slightly different colloquial use but functionally the same meaning. At NIH, we use nonpharmacologic more often and should use it instead of nonpharmacological for consistency.

Precision medicine

Historically, most medical treatments are designed for the "average patient" as a one-size-fits-all-approach. Precision medicine is an approach that considers individual differences in patients’ genes, environments, and lifestyles. Precision medicine is sometimes referred to as personalized medicine. NIH writing should use precision medicine rather than personalized medicine.

Rare disease

The Orphan Drug Act defines a rare disease as a disease or condition that affects fewer than 200,000 people in the United States. Only use this terminology when prevalence and/or incidence data are consistent with this criteria.

See the National Center for Advancing Translational Sciences’ Genetic and Rare Diseases Center website for more information.

Research subjects, control subjects, study participants

Research subjects have the particular characteristic, engage in the particular behavior, or are exposed to the particular variable (e.g., a certain drug) under study. Research subjects are recruited, selected, and observed.

Use patients, participants, or individuals instead of subjects when referring to human clinical trial participants, unless research subjects is specific to a policy or regulation. See: patients vs. subjects.

Control subjects make up the control group in a study and are used for comparison to the research participants. They are as similar as possible to the research participants but are not exposed to the condition or treatment being tested. Control subjects are recruited, selected, sometimes exposed to a placebo or standard treatment, and observed.

Study participants can be either research or control subjects.


A syndrome is a recognizable set of symptoms and physical findings that indicate a specific condition for which a direct cause is not necessarily understood. Once medical science identifies a causative agent or process with a high degree of certainty, physicians may then refer to the process as a disease, not a syndrome.

T cell, B cell

Only hyphenate as an adjective: e.g., T-cell therapy, B-cell leukemia.

Toxic, toxicity, toxin, toxicant

Toxic means “pertaining to or caused by a poison or toxin.”
Toxicity means “the quality, state, or degree of being poisonous.”
Toxins are natural poisons (e.g., snake venom).
Toxicants are manufactured poisons (e.g., chemical pesticides).

Vaccinate, inoculate, immunize

Of these three words, vaccinate has the narrowest definition: to give a vaccine to someone. Inoculate is more general and can mean to implant a virus, as is done in vaccines, or even to implant a toxic or harmful microorganism into something as part of scientific research. Immunize is the most general of the three words and can mean to grant immunity to a wide variety of things; it is sometimes used in legal language when referring to protection from unwanted legal action.

Variant, Variation, Mutant, Mutation,

Variant is the preferred term for any permanent DNA change. Variants in genes can cause disease, affect fetal development, or result in differences in how people’s bodies look or work, but they may not cause disease or have any effect at all. Exposure to some types of radiation, chemicals, or viral infections can produce variants, or they can be generated during cell division or DNA replication. Variants in egg or sperm cells can be passed on to offspring, while those in body cells aren't passed on.

Variation describes DNA sequence differences among individuals or populations.

Mutation has often been used to describe a disease-causing variant, if the change in the DNA sequence that’s described causes disease or if it’s induced during research(if the change is naturally occurring, use variant). While the term mutation is widely used and generally acceptable, it is not the preferred term for NIH writing.

Do not use mutant. Saying a gene is mutated or a research organism with a genetic change is a mutant can imply that a person with a similar genetic change is a mutant person.

This page last reviewed on January 17, 2024