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Diagnosis

The Laboratory Examination

Having learned the patient's clinical history and made his physical examination, the physician may then decide to submit specimens from the patient to a laboratory for testing. Fluids such as blood, urine, stomach fluid, or spinal fluid can be collected.

Basic laboratory tests of blood include a count of the number of white and red blood cells. An elevated number of white blood cells indicates an infection is present, but does not pinpoint the location of the infection. Blood also carries hormones and other components that are directly affected by disease or inflammation.

Far from the laboratory of the 1960s, the modern clinical laboratory is one of automation and high technology. Whereas before the laboratory technician was required to mix together the chemicals for each test, newer technology requires only that a blood specimen be placed in one end of a machine. The blood is carried through the machine and minute amounts of the chemicals are added as needed and the results printed out. This technology also enables the measurement of blood or urine components in amounts much smaller than previous technology allowed—often at microgram levels. A microgram is one millionth of a gram. To measure such a minute amount, the chemistry involved is precise and the reading of the results is beyond the capability of the human eye.

Both blood and urine may contain evidence of alcohol, illicit drugs, or toxic substances that the patient has taken. Infectious organisms from the blood or urine can be grown in culture dishes and examined to determine what they are. Bacteria in blood or urine are often too sparsely distributed to be seen under the microscope, but bacteria in a blood specimen wiped across a plate of culture medium will grow when the plate is placed in an incubator at body temperature.

The physician also may want to obtain x rays of an injured area to rule out the possibility of a fractured bone. The presence of a heart condition can often be determined by taking an electrocardiogram (ECG), which measures the electrical activity of the heart. Changes in the ECG can indicate the presence of heart disease or give evidence of a past heart attack. CAT (computerized axial tomography) scans use x rays to produce images of one layer of hard or soft tissue, a procedure useful in detecting small tumors. Magnetic resonance imaging (MRI) uses radio waves in a magnetic field to generate images of a layer of the brain, heart, or other organ. Ultrasound waves are also sometimes used to detect tumors.

Physicians can collect other kinds of information by injecting substances into the patient. Injection of radiopaque liquids, which block the passage of x rays, allow x-ray examination of soft tissues, such as the spinal cord, that are normally undetectable on x-ray photographs. Metabolic disorders can sometimes be pinpointed using a procedure called scintigraphy, in which a radioactive isotope is circulated through the body. A gamma camera is then used to record the concentration of the isotope in various tissues and organs.

Other laboratory specimens can be obtained by invasive techniques. If the physician finds a suspicious lump or swelling and needs to know its nature, he can remove part of the lump and send it to the laboratory to be examined. The surgical removal of tissue for testing is called a biopsy. In the laboratory, the specimen is sliced very thin, dyed to accentuate differences in tissues, and examined under the microscope. This enables the physician to determine whether the lump is malignant (cancerous) or benign (noncancerous). If it is cancer, further tests can determine if it is the primary tumor or if it has grown (metastasis) as a result of being spread from the primary tumor. Other tests can determine what kind of cancer it is.

The method of actually looking into the body cavity used to mean a major surgical procedure called a laparotomy. In that procedure, an incision was made in the abdomen so the physician could look at each organ and other internal structure in order and determine the presence of disease or parasite. Now the laparotomy is carried out using a flexible scope called a laparoscope, which is inserted into the body through a small incision. The scope is attached to a television monitor that gives the physician an enlarged view of the inside of the body. The flexibility of the scope allows it to be guided around the organs, and a light attached to the scope helps the physician see each organ. Also, the laparoscope is equipped with the means to collect biopsy specimens or suction blood out of the abdomen. Minor surgery can also be carried out to stop a bleeding blood vessel or remove a small growth from an organ.

Once the above steps the physician deems necessary have been carried out, he or she will then study the evidence collectively and arrive at a diagnosis. Once having determined the diagnosis, he or she can prescribe the proper treatment.

Larry Blaser

KEY TERMS

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Culture medium

—A substance that supports the growth of bacteria so they may be identified.

Invasive

—A technique that involves entering the body.

Pathology

—The study of changes in body tissues brought about by disease or injury.

Additional topics

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