Glossary

Find definitions for thousands of medical terms, treatments, and tests -- even health-related abbreviations, prefixes, and suffixes.

Filter by First Letter
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

N

Some medical tests report results in nanograms (ng) per liter (L).

  • A nanogram is one-billionth of a gram. A gram is about 1/30 of an ounce.
  • A liter is a measure of fluid volume. A liter is a little bigger than a quart of fluid.

Last Revised: May 6, 2011

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Thomas M. Bailey, MD - Family Medicine

Some medical tests report results in nanomoles (nmol). A mole is an amount of a substance that contains a large number (6 followed by 23 zeros) of molecules or atoms. A nanomole is one-millionth of a mole.

Last Revised: May 6, 2011

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Thomas M. Bailey, MD - Family Medicine

Some medical tests report results in nanomoles (nmol) per liter (L).

  • A mole is an amount of a substance that contains a large number (6 followed by 23 zeros) of molecules or atoms. A nanomole is one-billionth of a mole.
  • A liter measures fluid volume. It is a little bigger than a quart.

Last Revised: May 6, 2011

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Thomas M. Bailey, MD - Family Medicine

A narcotic (also called opioid or opiate) is a substance that can suppress perception of pain and calm the emotional response to pain by reducing the number of pain signals sent by the nervous system. Narcotics produce a feeling of well-being (euphoria) and cause mood changes, cloudy thinking, and deep sleep.

Commonly prescribed legal narcotics include butorphanol, codeine, hydrocodone, meperidine, and morphine. Heroin is an illegal narcotic. Side effects of narcotics may include constipation and nausea. Frequent use of narcotics may make a person dependent on them.

Last Revised: January 9, 2013

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Nancy Greenwald, MD - Physical Medicine and Rehabilitation

A nasal cannula is a flexible plastic tube that has a set of two prongs that can be placed in the nostrils. The tube is connected to an oxygen source.

Oxygen passes through the tube, through the openings in the prongs, and into the nostrils.

Last Revised: April 27, 2011

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Jennifer Merchant, MD - Neonatal-Perinatal Medicine

Nephrologists are medical doctors who specialize in the diagnosis and treatment of diseases of the kidney and urinary system, such as inflammation of the kidneys, chronic kidney disease, or cancer.

Nephrologists may further specialize in treating certain age groups, such as pediatric nephrologists, who only treat children. Nephrologists may consult with people for short-term illnesses or procedures, such as for a kidney biopsy. Or they may care for people who have long-term (chronic) kidney problems or who are on dialysis.

Nephrologists can be board-certified in nephrology through the American Board of Internal Medicine, which is recognized by the American Board of Medical Specialties.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

Nephrotic syndrome is a warning sign that something is damaging your kidneys. It causes high levels of protein in the urine and low levels of protein in the blood.

Many things can cause nephrotic syndrome, but the most common are kidney diseases and diabetes.

Nephrotic syndrome will usually get better if the cause is treated. But in some cases, it may lead to long-term kidney problems and kidney failure.

Last Revised: January 4, 2013

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & Tushar J. Vachharajani, MD, FASN, FACP - Nephrology

A neural tube defect (NTD) is a birth defect that occurs when the spine, the brain, or the bone and skin that protect them do not develop properly. The most common type of neural tube defect is spina bifida, in which the spinal cord or spinal nerves may bulge out through an opening in the bones of the spine.

The neural tube is the part of a developing fetus that grows into the spinal cord and brain. Normally, the bones of the skull and spine grow around the brain and spinal cord, and then skin covers the bones, creating the neural tube. A neural tube defect occurs when this process doesn't happen normally.

Neural tube defects can be found with prenatal tests, such as ultrasound and amniocentesis. In spina bifida, treatment depends on the severity. Surgery may be done to repair the spinal defect or to correct complications. Physical therapy, braces, and other treatments may be necessary to help the child with problems resulting from nerve damage.

Anencephaly is the second most common type of neural tube defect. In anencephaly, the infant is born with only a partially formed brain and spinal cord. This condition is always fatal.

Neural tube defects may be prevented if a woman takes folic acid before becoming pregnant and during the first 6 weeks of pregnancy. But often a woman does not know she is pregnant until after the first 6 weeks of pregnancy.

Last Revised: April 4, 2012

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Siobhan M. Dolan, MD, MPH - Reproductive Genetics

Neurological surgeons are medical doctors who specialize in surgery of the brain, spinal column, and nervous system.

A person may see a neurological surgeon for a problem such as a pinched nerve in the back or neck, a brain tumor, or damage to the brain or spine from an injury. A neurological surgeon may specialize in the treatment of one area of the body, such as the spinal column, or in the treatment of certain age groups. One example is a pediatric neurological surgeon, who only treats children.

Neurological surgeons can be board-certified by the Board of Neurological Surgery, which is recognized by the American Board of Medical Specialties.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

Neurologists are medical doctors who specialize in the diagnosis and treatment of brain, spinal cord, and nervous system diseases, such as multiple sclerosis, Alzheimer's disease, headaches, stroke, or injury.

A neurologist can order or interpret tests such as a computed tomography (CT) scan, magnetic resonance imaging (MRI), or lumbar puncture to diagnose problems and may conduct tests to evaluate how well a nerve or muscle is working. A neurologist can prescribe medicines to treat diseases or may refer a person to another specialist if needed.

Neurologists can be board-certified by the Board of Psychiatry and Neurology, which is recognized by the American Board of Medical Specialties.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

Neurotransmitters are chemicals produced by the nerve cells in the brain that send messages back and forth across the space between the cells (synapse). When the normal balance of these neurotransmitters is upset, headache, depression, or other mental health problems may develop.

The neurotransmitters that are believed to play a role in mental functioning are serotonin, norepinephrine, dopamine, and gamma-aminobutyric acid (GABA).

Last Revised: April 5, 2011

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Lisa S. Weinstock, MD - Psychiatry

When people use tobacco products on a regular basis, their bodies develop a need for nicotine. If they don't get nicotine, they start having nicotine withdrawal symptoms.

Withdrawal symptoms and cravings for nicotine vary from person to person. They often depend on how much nicotine a person is used to getting. The more nicotine the body is used to, the more severe symptoms are likely to be.

Symptoms of withdrawal include feeling:

  • Irritated.
  • Angry.
  • Anxious.
  • Restless.
  • Sad or depressed.
  • Hungrier than usual.

People going through withdrawal may find it hard to:

  • Sleep.
  • Cope with cravings.
  • Deal with stress.
  • Concentrate.

Nicotine withdrawal symptoms usually begin about 24 hours after a person quits smoking or using tobacco products. Symptoms are the worst in the first week or so after the person quits. The average length of time a person deals with withdrawal symptoms is 2 to 3 weeks. The craving for cigarettes and increased appetite can last for months.

Nicotine replacement products can reduce withdrawal symptoms when used by people who are quitting. Use of quit-smoking medicines, counseling or support groups, a nutritious diet, and regular exercise may also help.

Last Revised: July 6, 2011

Author: Healthwise Staff

Medical Review: Adam Husney, MD - Family Medicine & John Hughes, MD - Psychiatry

Nocturnal hypoglycemia refers to low blood sugar levels at night in a person who has diabetes. Blood sugar levels can drop below their target range at night if a person eats too little food after taking his or her usual nighttime insulin dose or takes more insulin than prescribed in the evening.

Low blood sugar can also happen when there are problems with the insulin (for example, it is expired or it has not been stored properly), when the amount of insulin changes (to find the right amount), or when the person with diabetes is sick.

But sometimes the reason is not obvious. Nocturnal hypoglycemia may also be related to previous exercise or increased physical activity.

Signs of low blood sugar at night include:

  • Restlessness, unusual noises, talking, or nightmares.
  • Waking up feeling tired or having a headache.
  • Having damp clothing and bed linens in the morning (night sweats).
  • Having a high blood sugar level in the morning.

Testing blood sugar levels at about 2 a.m. to 3 a.m. for a few consecutive nights may help a person find out whether low blood sugar is causing the symptoms. Continuous glucose monitoring (CGM) devices can also help. These devices sound an alarm when blood sugar is too high or too low.

Nocturnal hypoglycemia may be prevented by decreasing the evening insulin dose or by adding more food to the bedtime snack.

Last Revised: December 4, 2012

Author: Healthwise Staff

Medical Review: John Pope, MD - Pediatrics & Stephen LaFranchi, MD - Pediatrics, Pediatric Endocrinology

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used to relieve pain and fever and to reduce swelling and inflammation caused by injury or diseases such as arthritis. Aspirin, ibuprofen, ketoprofen, and naproxen are commonly used NSAIDs.

NSAIDs may cause side effects. The most common are stomach upset, heartburn, and nausea. Taking NSAIDs with food may help prevent these problems.

Frequent or long-term use of NSAIDs may lead to stomach ulcers or high blood pressure. They can also cause a severe allergic reaction.

  • NSAIDs have the potential to increase the risk of heart attack, stroke, skin reactions, and serious stomach and intestinal bleeding. These risks are greater if NSAIDs are taken at higher doses or for longer periods than recommended.
  • Aspirin, unlike other NSAIDs, has been shown to reduce the risk of heart attack and stroke. It does carry the risks of serious stomach and intestinal bleeding as well as skin reactions.
  • Because aspirin can increase the risk of bleeding, it is not recommended for new injuries. Take other medicines such as ibuprofen or naproxen for the first 2 or 3 days after an injury.

NSAIDs should be taken exactly as prescribed or according to the label. Taking a larger dose or taking the medicine longer than recommended can increase the risk of dangerous side effects.

Talk to your doctor about whether NSAIDs are right for you. People who are older than 65 or who have existing heart, stomach, kidney, liver, or intestinal disease are at higher risk for problems. For other people, the benefits may outweigh the risks.

Aspirin should not be given to anyone younger than 20 because of the risk of Reye syndrome, a rare but serious disease.

Last Revised: December 14, 2011

Author: Healthwise Staff

Medical Review: William H. Blahd, Jr., MD, FACEP - Emergency Medicine & Robert B. Keller, MD - Orthopedics

The normal sinus rhythm is the rate of impulses generated by certain muscle cells as a signal to the upper heart chambers (atria) to contract.

The heart contains a cluster of specialized muscle cells that act as the heart's natural pacemaker. This cluster is called the sinoatrial node, or SA node. The SA node generates the electrical signals that cause the upper heart chambers (atria) to contract. At rest, the SA node normally sends 60 to 100 impulses per minute (the normal sinus rhythm).

Last Revised: December 14, 2012

Author: Healthwise Staff

Medical Review: Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology & John M. Miller, MD, FACC - Cardiology, Electrophysiology

Nuclear medicine specialists are medical doctors who use radioactive medicines for diagnosis and treatment of certain problems.

Common nuclear medicine tests include bone scans, lung perfusion scans, and HIDA scans for gallbladder function.

Nuclear medicine specialists can be board-certified through the Board of Nuclear Medicine, which is recognized by the American Board of Medical Specialties.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

Nurse practitioners (NPs) are registered nurses (RNs) who have advanced education and clinical training. They can perform physical exams, diagnose and treat health problems, order lab work and X-rays, prescribe medicines, and provide health information.

Nurse practitioners may specialize in the care of children (pediatric nurse practitioner), older adults (geriatric nurse practitioner), people of all ages (family nurse practitioner), or people with mental health problems (psychiatric nurse practitioner).

Nurse practitioners are licensed by the state in which they practice. Most nurse practitioners are nationally certified in their specialty areas.

Last Revised: August 17, 2012

Author: Healthwise Staff

Medical Review: Anne C. Poinier, MD - Internal Medicine & E. Gregory Thompson, MD - Internal Medicine

Nutrients are substances in food that provide energy or are needed to support normal body functions. Nutrients are used to build and repair body tissues, including muscles, bones, and internal organs.

Nutrients include:

  • Carbohydrate.
  • Fat.
  • Protein.
  • Vitamins.
  • Minerals.
  • Water.

Last Revised: January 25, 2013

Author: Healthwise Staff

Medical Review: Kathleen Romito, MD - Family Medicine & Rhonda O'Brien, MS, RD, CDE - Certified Diabetes Educator