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Common Medical Tests

by Manuals Staff

A large number of tests are widely available. Many tests are specialized for a particular disorder or group of related disorders (which are usually described with the appropriate disorders in this book). Other tests are commonly used for a wide range of disorders.

Tests are done for a variety of reasons, including

  • Screening

  • Diagnosing a disorder

  • Evaluating the severity of a disorder so that treatment can be planned

  • Monitoring the response to treatment

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.

Types of Tests

There are different types of medical tests but the lines that separate them often become blurred. For example, endoscopy of the stomach enables the examiner to view the inside of the stomach as well as obtain tissue samples for examination in a laboratory. Tests are usually one of the six following types.

Analysis of Body Fluids

The most commonly analyzed fluids are

  • Blood

  • Urine

  • Fluid that surrounds the spinal cord and brain (cerebrospinal fluid)

  • Fluid within a joint (synovial fluid)

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.


These tests provide a picture of the inside of the body—in its entirety or only of certain parts (see see Overview of Imaging Tests). Ordinary x-rays are the most common imaging tests. Others include ultrasonography, radioisotope (nuclear) scanning, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and angiography.


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:

  • Nose: To examine the voice box (laryngoscopy) or the lungs (bronchoscopy)

  • Mouth: To examine the esophagus (esophagoscopy), stomach (gastroscopy), and small intestine (upper gastrointestinal endoscopy)

  • Anus: To examine the large intestine, rectum, and anus (coloscopy)

  • Urethra: To examine the bladder (cystoscopy)

  • Vagina: To examine the uterus (hysteroscopy)

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:

  • Joints (arthroscopy)

  • Abdominal cavity (laparoscopy)

  • Area of the chest between the lungs (mediastinoscopy)

  • Lungs and pleura (thoracoscopy)

Measurement of Body Functions

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.


Tissue samples are removed and examined, usually with 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.

Analysis of Genetic Material (Genetic Testing)

Usually, cells from skin, blood, or bone marrow are analyzed. Cells are examined to check for abnormalities of chromosomes, genes (including DNA), or both. Genetic testing may be done in the following:

  • Fetuses: To determine whether they have a genetic disorder

  • Children and young adults: To determine whether they have a disorder or are at risk of developing a disorder

  • Adults: Sometimes to help determine the likelihood that their relatives, such as children or grandchildren, will develop certain disorders

Risks and Results

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 table below 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.

Blood Tests*


Reference Range or Threshold (Conventional Units )

Acidity (pH)


Alcohol (ethanol)

0 mg/dL (more than 0.1 mg/dL usually indicates intoxication)


15–50 units/L


53–123 units/L

Antinuclear antibodies (ANA)

0 (negative result)

Ascorbic acid

0.4–1.5 mg/dL

Bicarbonate (carbon dioxide content)

18–23 mEq/L


Direct: Up to 0.4 mg/dL

Total: Up to 1.0 mg/dL

Blood volume

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)

35–45 mm Hg

Carboxyhemoglobin (carbon monoxide in hemoglobin)

Less than 5% of total hemoglobin

CD4 cell count

500–1500 cells/μL


15–60 mg/dL


98–106 mEq/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


70–150 μg/dL

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)


0.6–1.2 mg/dL


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


Male: 45–52%

Female: 37–48%


Male: 13–18 g/dL

Female: 12–16 g/dL


60–160 μg/dL (higher in males)

Iron-binding capacity

250–460 μg/dL

Lactate (lactic acid)

Venous: 4.5–19.8 mg/dL

Arterial: 4.5–14.4 mg/dL

Lactic dehydrogenase

50–150 units/L


20 μg/dL or less (much lower in children)


10–150 units/L


Cholesterol, total

Less than 225 mg/dL (for age 40–49 yr; increases with age)

High-density lipoprotein (HDL)

30–70 mg/dL

Low-density lipoprotein (LDL)

60 mg/dL


40–200 mg/dL (higher in males)

Liver function tests

Include bilirubin (total), phosphatase (alkaline), protein (total and albumin), transaminases (alanine and aspartate), prothrombin


1.5–2.0 mg/dL

Mean corpuscular hemoglobin (MCH)

27–32 pg/cell

Mean corpuscular hemoglobin concentration (MCHC)

32–36% hemoglobin/cell

Mean corpuscular volume (MCV)

76–100 cubic μm


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)

83–100 mm Hg

Oxygen saturation (arterial)


Partial thromboplastin time (PTT)

30–45 seconds

Phosphatase (alkaline)

50–160 units/L (higher in infants and adolescents, lower in females)


3.0–4.5 mg/dL

Platelet count



3.5–5.0 mEq/L

Prostate-specific antigen (PSA)

0–4 ng/mL (increases with age)



6.0–8.4 g/dL


3.5–5.0 g/dL


2.3–3.5 g/dL

Prothrombin time (PT)

10–13 seconds

Red blood cell (RBC) count

4.2–5.9 million/mL


135–145 mEq/L

Thyroid-stimulating hormone (TSH)

0.5–5.0 m units/L

Transaminases (liver enzymes):

Alanine (ALT)

1–21 units/L

Aspartate (AST)

7–27 units/L

Troponin in its different forms:


Less than 1.6 ng/mL


Less than 0.1 ng/mL

Urea nitrogen (BUN)

7–18 mg/dL

Uric acid

3.0–7.0 mg/dL

Vitamin A §

30–65 μg/dL

White blood cell (WBC) count

4,300–10,800 /mL

*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.

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

Arteriography (angiography)

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

Usually an arm

Test for high or low blood pressure, usually using an inflatable cuff wrapped around the arm

Blood tests

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

Cardiac catheterization


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

Chromosomal analysis


Examination under a microscope to detect a genetic disorder or to determine a fetus’s sex


Large intestine

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

Cone biopsy


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

Electrocardiography (ECG)


Study of the heart’s electrical activity using electrodes attached to the arms, legs, and chest

Electroencephalography (EEG)


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

Electrophysiologic testing


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)

Biliary tract

X-ray study of the biliary tract done after injection of a radiopaque dye and using a flexible viewing tube


Digestive tract

Direct examination of internal structures using a flexible viewing tube

Enzyme-linked immunosorbent assay (ELISA)

Usually blood

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

Intravenous urography

Kidneys and urinary tract

X-ray study of the kidneys and urinary tract after a radiopaque dye is injected into a vein (intravenously)

Joint aspiration

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


Spinal column

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

Large intestine

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

Radionuclide imaging

Many organs

Imaging test using particles that release radiation (radionuclides) to detect abnormalities in blood flow, structure, or function

Reflex tests


Tests using a physical stimulus (such as a light tap) to detect abnormalities in nerve function

Retrograde urography

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)

Spinal canal

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

Stress testing


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

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