So far we have established that disease leads to lack of homeostasis in the body. In order to accurately diagnose disease (or lack of stasis), your doctor will use a combination of strategies which may include checking vital signs, physical examination, running laboratory tests, and imaging parts of your body. Explore these techniques to discover how doctors diagnose diseases.

Vital Signs

Vital signs are routinely used as indicators of health status. They include pulse rate, temperature, respiration rate, and blood pressure. The normal vital signs for an average healthy adult are as follows:

  • Pulse rate: 60-100 beats per minute
  • Temperature: 97.8°F to 99.1°F (36.5°C to 37.3°C)
  • Respiration (breathing) rate: 12-18 breaths per minute
  • Blood pressure: 90/60 mm Hg to 120/80 mm Hg

Physical Examination

physical examination may include inspection, palpation, auscultation and percussion. The purpose of inspection is to determine abnormalities on the surface of the body. Palpation involves using touch to detect the location, size or texture of an abnormality, or the location of pain. Auscultation is a listening technique usually utilizing the use of a stethoscope to listen for abnormal sounds of organs such as the heart, lungs and intestines. Percussion is another listening technique but it requires that the examiner produce a sound by tapping on a specific part of the body with the fingers. The sound that is produced can be used to tell the nature of a mass in the body, for example, whether it is solid, fluid-filled or gas-filled. It can also indicate the borders, and hence the shape and size of an organ.

Laboratory Tests

In order to collect further confirmation of disease status, your doctor may require laboratory tests on your fluid or excreta samples. For example, blood, urine, tissue, stool, sputum (spit) and swabs. Routine blood tests may include:

  1. Complete Blood Count (CBC): For checking total red blood cells, white blood cells, hemoglobin, and platelets
  2. Comprehensive Metabolic Panel (CMP): For checking glucose, protein, calcium, electrolytes, enzymes, urea, and more
  3. Diabetes screen: For checking fasting glucose level
  4. Lipid Panel: For checking total cholesterol, LDL (“bad”) cholesterol, HDL (“good”) cholesterol, and triglycerides


Further confirmation of disease may be done using imaging techniques to study internal components of the body that could not otherwise be visualized. Common techniques used include electrocardiography, radiography, computed tomography (CT) scan, magnetic resonance imaging (MRI), ultrasound, nuclear medicine, and the use of scopes (cameras inserted in the body). 


Electrical current generated by the heart is spread throughout the body. The currents can be detected and amplified using an instrument called an electrocardiogram. The instrument generates a graph known as an electrocardiograph which a doctor can read to determine if the heart is beating normally or abnormally.


An X-ray is a type of light along the electromagnetic light spectrum just like visible light. However, unlike visible light, it is invisible. When shone onto the body, x-rays pass through muscle but is absorbed in hard structures like bones and teeth. This difference in light absorption creates bright and dark regions. Bones and teeth appears bright while muscle appears dull. 

Computed Tomography (CT) Scan

A computed tomography or CT scan combines x-ray with computer technology. The x-ray in a CT scan is applied over a wide region, making it possible to get 3D images. A good way of looking at the difference is that the traditional x-ray takes pictures from only one angle while a CT scan takes pictures from many angles. The images can then be viewed as slices or stacked together to show full three-dimensional images.

Magnetic Resonance Imaging (MRI)

A magnetic resonance image (MRI) machine creates images based on the amount of energy released by different tissues in the body. When exposed to the MRI, water molecules (specifically, protons in water molecules) align in the direction of the magnet. A radio wave is then added to the system, which gives more energy to the protons. This causes them to shift their direction of alignment. When the radio wave is removed, the protons go back to their position, releasing energy in the process. This energy is detected and converted to an image. Since the MRI uses a powerful magnet, a patient taking an MRI scan must remove all metal such as jewelry before going in the machine. The presence of metal implants from surgery may cause injury and hence will likely prevent you from taking an MRI. 


An ultrasound machine creates images using high-frequency sound waves. Because the sound is outside of the range of human hearing, we call it “ultrasound”. To get an image, ultrasound created by the machine hits the organ of interest, some of which bounces back to the machine. The echo is converted to electrical signals and finally an image. 

Nuclear Medicine  

Nuclear medicine is a medicine that contains a radioactive chemical. The medicine can be inhaled, swallowed or injected. For faster action, it is injected. Once in the body, the radioactive substance travels to the organ of interest where it is absorbed and releases radiation. The radiation that is given off is captured and used to create an image of the organ.

Medical Scopes

Doctors can view and investigate internal organs using one of several scope (viewing) instruments. An endoscope for example is used to examine the upper gastrointestinal system. The instrument consists of a long flexible tube fitted with a camera. The doctor will place it into the mouth of the patient, through the throat, esophagus, stomach and upper intestine. The procedure is able to detect any infection, inflammation, or tumors that may be present. A biopsy may be taken during the procedure for further examination. Examples of other types of scope applications include:

Bronchoscopes: For examination of lungs

Cytoscope: For examination of bladder

Ureteroscope: For examination of ureter

Arthroscope: For examination of joins

Colonoscope: For examination of colon


Doctors use a combination of observation, sensory evaluation (sign, touch, hearing), laboratory tests of body fluids, and imaging to accurately diagnose disease and determine the health of their patients. Now that you are familiar with these techniques, you will have a better understanding of what your doctor is doing the next time you go for a checkup. Hopefully, this will lead you to ask him/her the right questions.

Courtney Simons
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.
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