How Reliable is Laboratory Testing?

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Evaluating Test Results in a Clinical Context – why do tests sometimes need to be repeated?

The doctor is expected to evaluate all the relevant findings – laboratory test data plus information from other sources, such as physical exam, personal and family histories, signs and symptoms, other diagnostic examinations, i.e., x-rays, ECG, 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. The clinician must always ask, “Do the test data fit with the other pieces of the puzzle?” Careful evaluation and consideration of test findings increases the reliability of a diagnosis and reduces the chance of medical errors.


As this diagram shows, data from medical tests are part of the information set that needs to be considered when a doctor makes a diagnosis. When a laboratory report indicates abnormal or unexpected results, it is necessary 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 to eliminate transient or spurious results.

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 nurse 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.

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