Medical Lab Tests

There are numerous tests that are widely available. Many tests are specialized for a particular disorder or group of related disorders while some 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

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)

Sweat, saliva, and fluid from the digestive tract can be analyzed as well.

Imaging:

These tests provide a picture of the inside of the body. X-rays are the most common imaging tests. Others include ultrasonography/ultrasound, computed tomography (CT), magnetic resonance imaging (MRI) and angiography.

Endoscopy:

An endoscope is used to directly see the inner part of body organs or spaces/cavities. The tip of the endoscope is 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 can be passed through the channel in the endoscope, most commonly 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)

Sometimes a small cut is made through the skin and tissue layers to enable the endoscope to be passed into a body cavity. These are used to view the the following:

  • Joints (arthroscopy)
  • Abdominal cavity (laparoscopy)
  • Area of the chest between the lungs (mediastinoscopy)
  • Lungs and pleura (thoracoscopy)

Measurement of Body Functions:

Body functions can be measured by recording and analyzing the activity of various organs. The 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/lung function test/spirometry.

Biopsy:

Tissue samples are removed and examined microscopically and biochemically. These are focused on finding abnormal cells that may indicate inflammation or of a disorder, such as cancer. Tissues that are usually examined include skin, breast, lung, liver, kidney, and bone.

Analysis of Genetic Material (Genetic Testing):

Cells from skin, blood, or bone marrow are analyzed to check for abnormalities of chromosomes, genes and DNA. Genetic testing may be required 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*

Test Reference Range or Threshold (Conventional Units)
Acidity (pH) 7.35–7.45
Alcohol (ethanol) 0 mg/dL (more than 0.1 mg/dL usually indicates intoxication)
Ammonia 15–50 units/L
Amylase 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
Bilirubin Direct: Up to 0.4 mg/dL
Total: Up to 1.0 mg/dL
Blood volume 8.5–9.1% of body weight
Calcium 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
Ceruloplasmin 15–60 mg/dL
Chloride 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
Copper 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)
Creatinine 0.6–1.2 mg/dL
Electrolytes 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
Glucose Fasting: 70–110 mg/dL
Hematocrit Male: 45–52%
Female: 37–48%
Hemoglobin Male: 13–18 g/dL
Female: 12–16 g/dL
Iron 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
Lead 20 μg/dL or less (much lower in children)
Lipase 10–150 units/L
Lipids:
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
Triglycerides 40–200 mg/dL (higher in males)
Liver function tests Include bilirubin (total), phosphatase (alkaline), protein (total and albumin), transaminases (alanine and aspartate), prothrombin
Magnesium 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
Osmolality 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) 96–100%
Partial thromboplastin time (PTT) 30–45 seconds
Phosphatase (alkaline) 50–160 units/L (higher in infants and adolescents, lower in females)
Phosphorus 3.0–4.5 mg/dL
Platelet count 150,000–350,000/mL
Potassium 3.5–5.0 mEq/L
Prostate-specific antigen (PSA) 0–4 ng/mL (increases with age)
Protein:
Total 6.0–8.4 g/dL
Albumin 3.5–5.0 g/dL
Globulin 2.3–3.5 g/dL
Prothrombin time (PT) 10–13 seconds
Red blood cell (RBC) count 4.2–5.9 million/mL
Sodium 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:
I Less than 1.6 ng/mL
T 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

Procedure Body Area or Sample Tested Description
Amniocentesis 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
Audiometry Ears Assessment of the ability to hear and distinguish sounds at specific pitches and volumes using headphones
Auscultation Heart 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
Biopsy 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
Bronchoscopy Airways of the lungs Direct examination with a viewing tube to check for a tumor or other abnormality
Cardiac catheterization Heart Study of heart function and structure using a catheter inserted into a blood vessel and threaded to the heart
Chorionic villus sampling Placenta Removal of a sample for examination under a microscope to check for abnormalities in the fetus
Chromosomal analysis Blood Examination under a microscope to detect a genetic disorder or to determine a fetus’s sex
Colonoscopy Large intestine Direct examination with a viewing tube to check for a tumor or other abnormality
Colposcopy Cervix 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 Cervix Removal and examination of a cone-shaped piece of tissue, usually using a heated wire loop or a laser
Culture 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
Echocardiography Heart Study of heart structure and function using sound waves
Electrocardiography (ECG) Heart Study of the heart’s electrical activity using electrodes attached to the arms, legs, and chest
Electroencephalography (EEG) Brain Study of the brain’s electrical function using electrodes attached to the scalp
Electromyography Muscles Recording of a muscle’s electrical activity using small needles inserted into the muscle
Electrophysiologic testing Heart 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
Endoscopy 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
Fluoroscopy Digestive tract, heart, or lungs A continuous x-ray study that enables a doctor to see the inside of an organ as it functions
Hysteroscopy Uterus 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
Laparoscopy Abdomen 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
Mammography Breasts X-ray study to check for breast cancer
Mediastinoscopy Chest Direct examination of the area of the chest between the lungs using a viewing tube inserted through a small incision just above the breastbone
Myelography Spinal column Simple or computer-enhanced x-ray study of the spinal column after injection of a radiopaque dye
Nerve conduction study Nerves 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
Ophthalmoscopy Eyes Direct examination using a handheld device that shines light into the eye to detect abnormalities inside the eye
Papanicolaou (Pap) test Cervix Examination of cells scraped from the cervix under a microscope to detect cancer
Paracentesis Abdomen 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 Lungs 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 Tendons 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
Sigmoidoscopy 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
Spirometry Lungs Test of lung function that involves blowing into a measuring device
Stress testing Heart 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)
Thoracentesis 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
Thoracoscopy Lungs Examination of the lung surfaces, pleura, and pleural space through a viewing tube
Tympanometry Ears 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
Urinalysis Kidneys and urinary tract Chemical analysis of a urine sample to detect protein, sugar, ketones, and blood cells
Venography Veins X-ray study using a radiopaque dye (similar to arteriography) to detect blockage of a vein