Laboratory Medicine: Tests Can Often Yield Answers

All doctors rely on laboratory tests in making many of their medical decisions. Some tests may be done on samples of blood, urine, or body tissue. For others, the patient may be sent to a special laboratory for X-rays, function studies or scans, imaging, or certain invasive procedures such as colonoscopy. The following are some of the more common tests that you may encounter as part of a diagnostic process.


Urine studies are the oldest medical tests. Ancient physicians diagnosed disease by studying the color and smell of urine, and some even tasted it. By this last method, early Greek physicians could discern diabetes, when the urine had a sweet taste because of the presence of blood sugar, or glucose. Today, urine is studied not only for glucose, but also for blood cells, protein, bacteria, hormones, and chemicals. Some urine tests can be done at home. Included are early pregnancy tests, which can now detect pregnancy as soon as two weeks after conception; and a glucose test, in which chemical strips dipped in a urine sample can detect sugar, a sign that diabetes is out of control. For other analyses, the urine specimen may be collected at home or in a doctors office, and then sent to a laboratory.

Blood Tests

Your blood speaks volumes about your health, and blood tests can detect many conditions long before any symptoms appear. Certain of these tests involve measuring levels of substances carried in the blood, such as cholesterol, hormones, enzymes, drugs, and numerous body chemicals. A biochemical profile, which may involve 40 or more such measurements, can now be done very quickly in a sequential multiple analyzer (SMA) machine with just one or two test tubes of blood. The results are reported on a computer printout that compares your numbers with normal ones.

Although automated blood analysis is fast and relatively inexpensive, errors are common, and you should not be unduly alarmed by an abnormal result. In such cases, a second, less automated, and more precise test will be done to confirm the results of the first one.

Other tests involve looking through a microscope at the blood cells themselves. For a total blood count, the numbers of different blood cells in a specific amount of blood are estimated. The size, shapes, and color of the cells may also be studied, especially if sickle cell disease, anemia, leukemia, or another type of blood disorder is suspected.


These tests require examination of a sample of tissue under a microscope for abnormalities. In some biopsies, a tumor or piece of tissue is removed surgically. In other cases, such as in a bone, liver, or breast biopsy, the sample may be obtained by aspiration with a hollow needle inserted through the skin and overlying tissue.

Pap Smear

This test involves scraping cells from the surface of a woman's cervix and then studying them microscopically for abnormalities that indicate possible cancer. Pap smears, which are included as part of most gynecological examinations, should be performed every one to three years.

Function Tests

These are diagnostic studies done in special laboratories to assess how well an organ or organ system is functioning. Common examples include hearing and vision tests, spirometry to assess lung function, exercise stress tests to study cardiovascular capability, and nerve and muscle studies. In some cases, such as a fertility workup, function tests are usually combined with other types of laboratory analyses.

The Cost Factor

In recent years, testing has emerged as the fastest growing and most costly aspect of medical care in the United States. Computers and other technological advances are responsible for much of this growth, but changes in medical practice are also a factor. For example, many doctors say they order tests as a protective measure against malpractice suits, even though they may not expect the results to alter treatment. Others perhaps use tests to boost income, because they can charge higher fees (and are more likely to be reimbursed by insurance and other third-party payers) for tests and procedures than for time spent counseling their patients in preventive measures.

In some instances, costly screening tests only rarely uncover an abnormality, raising the question of whether they are cost-effective. For example, ultrasound is now performed frequently during pregnancy to screen for certain birth defects and determine fetal age. Some economists question whether this is an appropriate use of medical resources because the large majority of pregnancies are normal. As an alternative, they suggest that ultrasound be reserved for high-risk pregnancies or those in which a problem is already suspected.

Cost is not the only issue — many tests are uncomfortable and some carry a risk of complications. As a patient, you can protect yourself from being given any unnecessary tests by asking the following questions:

  • Why do I need this test?
  • Is it painful?
  • Is there any risk of complications?
  • How accurate, usually, are the results?
  • Am 1 likely to need additional tests?
  • How will the results be used?
  • Will the results affect the course of my treatment?
  • What will happen if I don't have the test?
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