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How Reliable is Laboratory Testing?

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My test results came back from the lab and my doctor wants me to repeat the test. Why?

The health care provider is expected to evaluate all of the relevant findings – laboratory test data plus information from other sources, such as physical exam, personal and family histories, signs and symptoms, and other diagnostic examinations, i.e., x-rays, EKG, etc. – before settling on a diagnosis and developing a treatment plan. Given the complexities in human physiology and disease response, no diagnosis should ever be made solely on the basis of a single lab test [see the article "Being Misread: A Lesson in Vigilance"]. The clinician must always ask, "Do the test data fit with the other pieces of the puzzle?" Careful evaluation and consideration of test findings increase the reliability of a diagnosis and can reduce the chance of medical errors.

Information sources critical to diagnostic process

As this diagram shows, data from medical tests are part of the information set that needs to be considered when a health care provider makes a diagnosis. When a laboratory report indicates abnormal or unexpected results, it is incumbent for your health care provider to further evaluate and corroborate the information at hand to ensure an accurate diagnosis. If the data do not correspond with the clinical picture, additional information may be needed and retesting may be appropriate. In some situations, the progression of the disease or condition may not be evident for the testing modality to be relevant; i.e., a false-negative pregnancy test performed too soon after conception.

Is there anything I can do?

Yes. Sometimes there are things you do or don’t do that can affect your tests results. Following a couple of guidelines can help to ensure that your results are interpreted correctly by your doctor:

  • Your doctor or his office staff should discuss with you how to prepare for a test to avoid known interferences. You may be instructed to fast or avoid certain foods or activities. Carefully follow these instructions to prepare for the test.
  • Since some test results can be affected by medications, vitamins, and other over-the-counter health supplements, it is important that you provide a complete and honest medical history so that your doctor can correctly interpret the results from the lab.

If you and your provider are surprised by a test result, here are some questions you could discuss together.

  1. Is the result consistent with my symptoms and current health state?
  2. How often do false negative or false positive results occur with this test?
  3. Is the course of action being considered serious enough that we should retest?
  4. Do we have any reason to doubt the quality of the findings?
  5. Would it be appropriate in this case to get a second opinion?

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