A large number of medical tests are widely available. Many tests are used for a particular disorder or group of related disorders. Other tests are commonly used for a wide range of disorders.
Tests are done for a variety of reasons, including
Sometimes a test is used for more than one purpose. A blood test may show that a person has too few red blood cells (anemia). The same test may be repeated after treatment to determine whether the number of red blood cells has returned to normal. Sometimes a disorder can be treated at the same time a screening or diagnostic test is done. For example, when colonoscopy (examination of the inside of the large intestine with a flexible viewing tube) detects growths (polyps), they can be removed before colonoscopy is completed.
Some Diagnostic Procedures
Body Area or Sample Tested
Fluid from the sac surrounding the fetus
Analysis of fluid, removed by a needle inserted through the abdominal wall, to detect an abnormality in the fetus
Any artery in the body, commonly in the brain, heart, kidneys, aorta, or legs
X-ray study using radiopaque dye injected through a thin tube (catheter), which is threaded to the artery being studied, to detect and outline or highlight a blockage or defect in an artery
Assessment of the ability to hear and distinguish sounds at specific pitches and volumes using headphones
Listening with a stethoscope for abnormal heart sounds
Barium x-ray studies
Esophagus, stomach, intestine, or rectum
X-ray study to detect ulcers, tumors, or other abnormalities
Any tissue in the body
Removal and examination of a tissue sample under a microscope to check for cancer or another abnormality
Blood pressure measurement
Test for high or low blood pressure, usually using an inflatable cuff wrapped around the arm
Usually a blood sample from an arm
Measurement of substances in the blood to evaluate organ function and to help diagnose and monitor various disorders
Bone marrow aspiration
Hipbone or breastbone
Removal of a bone marrow sample by a needle for examination under a microscope to check for abnormalities in blood cells
Airways of the lungs
Direct examination with a viewing tube to check for a tumor or other abnormality
Study of heart function and structure using a catheter inserted into a blood vessel and threaded to the heart
Chorionic villus sampling
Removal of a sample for examination under a microscope to check for abnormalities in the fetus
Examination under a microscope to detect a genetic disorder or to determine a fetus’s sex
Direct examination with a viewing tube to check for a tumor or other abnormality
Direct examination of the cervix with a magnifying lens
Computed tomography (CT)
Any part of the body
Computer-enhanced x-ray study to detect structural abnormalities
Removal and examination of a cone-shaped piece of tissue, usually using a heated wire loop or a laser
A sample from any area of the body (usually a fluid such as blood or urine)
Growth and examination of microorganisms from the sample to identify infection with bacteria or fungi
Dilation and curettage (D and C)
Cervix and uterus
Examination of a sample under a microscope to check for abnormalities in the uterine lining using a small, sharp instrument (curet).
Dual x-ray absorptiometry (DEXA)
Skeleton, focusing on specific regions, usually the hip, spine, and wrist
Low-dose x-ray study to determine the thickness of bones
Study of heart structure and function using sound waves
Study of the heart’s electrical activity using electrodes attached to the arms, legs, and chest
Study of the brain’s electrical function using electrodes attached to the scalp
Recording of a muscle’s electrical activity using small needles inserted into the muscle
Test to evaluate rhythm or electrical conduction abnormalities using a catheter inserted into a blood vessel and threaded to the heart
Endoscopic retrograde cholangiopancreatography (ERCP)
X-ray study of the biliary tract done after injection of a radiopaque dye and using a flexible viewing tube
Direct examination of internal structures using a flexible viewing tube
Enzyme-linked immunosorbent assay (ELISA)
Test that involves mixing the sample of blood with substances that can trigger allergies (allergens) or with microorganisms to test for the presence of specific antibodies
Digestive tract, heart, or lungs
A continuous x-ray study that enables a doctor to see the inside of an organ as it functions
Direct examination of the inside of the uterus with a flexible viewing tube
Kidneys and urinary tract
X-ray study of the kidneys and urinary tract after a radiopaque dye is injected into a vein (intravenously)
Joints, especially those of the shoulders, elbows, fingers, hips, knees, ankles, and toes
Removal and examination of fluid from the space within joints to check for blood cells, crystals formed from minerals, and microorganisms
Direct examination using a viewing tube inserted through an incision in the abdomen to diagnose and treat abnormalities in the abdomen
Magnetic resonance imaging (MRI)
Any part of the body
Imaging test using a strong magnetic field and radio waves to check for structural abnormalities
X-ray study to check for breast cancer
Direct examination of the area of the chest between the lungs using a viewing tube inserted through a small incision just above the breastbone
Simple or computer-enhanced x-ray study of the spinal column after injection of a radiopaque dye
Nerve conduction study
Test to determine how fast a nerve impulse travels using electrodes or needles inserted along the path of the nerve
Occult blood test
Test to detect blood in stool
Direct examination using a handheld device that shines light into the eye to detect abnormalities inside the eye
Papanicolaou (Pap) test
Examination of cells scraped from the cervix under a microscope to detect cancer
Insertion of a needle into the abdominal cavity to remove fluid for examination
Percutaneous transhepatic cholangiography
Liver and biliary tract
X-ray study of the liver and biliary tract after a radiopaque dye is injected into the liver
Positron emission tomography (PET)
Brain and heart
Imaging test using particles that release radiation (positrons) to detect abnormalities in function
Pulmonary function tests
Tests to measure the lungs’ capacity to hold air, to move air in and out of the body, and to exchange oxygen and carbon dioxide as people blow into a measuring device
Imaging test using particles that release radiation (radionuclides) to detect abnormalities in blood flow, structure, or function
Tests using a physical stimulus (such as a light tap) to detect abnormalities in nerve function
Bladder and ureters
X-ray study of the bladder and ureters after a radiopaque dye is inserted into the ureter
Rectum and last portion of the large intestine
Direct examination using a viewing tube to detect tumors or other abnormalities
Skin allergy tests
Usually an arm or the back
Tests for allergies done by placing a solution containing a possible allergen on the skin, then pricking the skin with a needle
Spinal tap (lumbar puncture)
Removal of spinal fluid, using a needle inserted into the hipbone, to check for abnormalities in spinal fluid
Test of lung function that involves blowing into a measuring device
Test of heart function during exertion using a treadmill or other exercise machine and electrocardiography (if people cannot exercise, a drug is used to simulate exercise’s effects)
The space between the pleura, a two-layered membrane that covers the lungs and lines the chest wall (pleural space)
Removal of fluid from this space with a needle to detect abnormalities
Examination of the lung surfaces, pleura, and pleural space through a viewing tube
Measurement of the resistance to pressure (impedance) in the middle ear using a device inserted in the ear and sound waves to help determine the cause of hearing loss
Ultrasonography (ultrasound scanning)
Any part of the body
Imaging using sound waves to detect structural or functional abnormalities
Kidneys and urinary tract
Chemical analysis of a urine sample to detect protein, sugar, ketones, and blood cells
X-ray study using a radiopaque dye (similar to arteriography) to detect blockage of a vein
Tests are usually one of the six following types.
The most commonly analyzed fluids are
Less often, sweat, saliva, and fluid from the digestive tract (such as gastric juices) are analyzed. Sometimes the fluids analyzed are present only if a disorder is present, as when fluid collects in the abdomen, causing ascites, or in the space between the two-layered membrane covering the lungs and lining the chest wall (pleura), causing pleural effusion.
Reference Range or Threshold (Conventional Units † )
0 mg/dL (more than 0.1 mg/dL usually indicates intoxication)
Antinuclear antibodies (ANA) ‡
0 (negative result)
Bicarbonate (carbon dioxide content)
Direct: Up to 0.4 mg/dL
Total: Up to 1.0 mg/dL
8.5–9.1% of body weight
8.5–10.5 mg/dL (slightly higher in children)
Carbon dioxide pressure (expressed as a comparison with how high the level of mercury [Hg] rises in a tube due to air pressure at sea level)
Carboxyhemoglobin (carbon monoxide in hemoglobin)
Less than 5% of total hemoglobin
500–1500 cells/ μ L
Complete blood cell count (CBC)
See individual tests: Hemoglobin, hematocrit, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, mean corpuscular volume, platelet count, and white blood cell count
Creatine kinase (CK), also called creatine phosphokinase (CPK)
Male: 38–174 units/L
Female: 96–140 units/L
Creatine kinase (CK) in its different forms (isoenzymes)
5% or less of CK-MB (the form that occurs mainly in heart muscle)
See individual tests: Calcium, chloride, magnesium, potassium, and sodium (which are routinely tested)
Erythrocyte sedimentation rate (ESR)
Male: 1–13 mm/hour
Female: 1–20 mm/hour
Fasting: 70–110 mg/dL
Female: 37–48%
Male: 13–18 g/dL
Female: 12–16 g/dL
60–160 μ g/dL (higher in males)
Lactate (lactic acid)
Venous: 4.5–19.8 mg/dL
Arterial: 4.5–14.4 mg/dL
20 μ g/dL or less (much lower in children)
Less than 225 mg/dL (for age 40–49 yr; increases with age)
High-density lipoprotein (HDL)
Low-density lipoprotein (LDL)
40–200 mg/dL (higher in males)
Liver function tests
Mean corpuscular hemoglobin (MCH)
Mean corpuscular hemoglobin concentration (MCHC)
Mean corpuscular volume (MCV)
76–100 cubic μ m
280–296 mOsm/kg plasma
Oxygen pressure (expressed as a comparison with the level of mercury [Hg] in a tube, which results from air pressure at sea level)
Oxygen saturation (arterial)
Partial thromboplastin time (PTT)
50–160 units/L (higher in infants and adolescents, lower in females)
Prostate-specific antigen (PSA)
0–4 ng/mL (increases with age)
Prothrombin time (PT)
Red blood cell (RBC) count
Thyroid-stimulating hormone (TSH)
Transaminases (liver enzymes):
Troponin in its different forms:
Less than 1.6 ng/mL
Less than 0.1 ng/mL
White blood cell (WBC) count
*Blood can be tested for many other substances as well.
† Units are explained in Appendix I. Conventional units can be converted to international units by using a conversion factor. International units (IU), a different system, are sometimes used by laboratories.
‡ Other antibodies can also be identified.
§ Other vitamins can also be measured.
Imaging tests provide a picture of the body’s interior—of the whole body or part of it. Imaging helps doctors diagnose a disorder, determine how severe the disorder is, and monitor people after the disorder is diagnosed. Most imaging tests are painless, relatively safe, and noninvasive (that is, they do not require an incision in the skin or the insertion of an instrument into the body).
Imaging tests may use the following:
There are some risks of using radiation in medical imaging.
For information regarding imaging tests common for specific diagnoses and screenings, see the following:
A viewing tube (endoscope) is used to directly observe the inside of body organs or spaces (cavities). Most often, a flexible endoscope is used, but in some cases, a rigid one is more useful. The tip of the endoscope is usually equipped with a light and a camera, so the examiner watches the images on a television monitor rather than looking directly through the endoscope. Tools are often passed through a channel in the endoscope. One type of tool is used to cut and remove tissue samples.
Endoscopy usually consists of passing the viewing tube through an existing body opening, such as the following:
However, sometimes an opening in the body must be created. A small cut (incision) is made through the skin and the layers of tissue beneath the skin, so that the endoscope can be passed into a body cavity. Such incisions are used to view the inside of the following:
Often, body functions are measured by recording and analyzing the activity of various organs. For example, electrical activity of the heart is measured with electrocardiography (ECG) , and electrical activity of the brain is measured with electroencephalography (EEG) . The lungs’ ability to hold air, to move air in and out, and to exchange oxygen and carbon dioxide is measured with pulmonary function tests .
A biopsy is a procedure in which a sample of tissue is removed from the body for examination. A diagnosis is made when cells are examined through a microscope. The examination often focuses on finding abnormal cells that may provide evidence of inflammation or of a disorder, such as cancer. Tissues that are commonly examined include skin, breast, lung, liver, kidney, and bone.
Genetic diagnostic technologies are scientific methods that are used to understand and evaluate chromosomes , genes (including DNA ), or both. Usually, cells from skin, blood, or bone marrow are analyzed. Genetic testing may be done in the following:
Genetic diagnostic technology is rapidly improving. Various methods may be used to copy segments of a gene or to find changes in genes.
Every test has some risk. The risk may be the possibility of injury during the test, or it may be the need for further testing if the result is abnormal. Further testing is often more expensive, dangerous, or both. Doctors weigh the risk of a test against the usefulness of the information it will provide.
Normal test values are expressed as a range, which is based on the average values in a healthy population. That is, 95% of healthy people have values within this range. However, average values are slightly different for women and men and may vary by age. For some tests, these values also vary among laboratories. Thus, when doctors get a laboratory test result, the laboratory also gives them its own normal range for that test. The Blood Tests table lists some typical normal results. However, because values vary by laboratory, people should consult their doctor about the significance of their own test results rather than refer to this table.