Understanding Your Medical Test Results

What Positive, Negative, and Relative Values Mean

There are thousands of medical tests used on patients to diagnose, measure the progression of a disease or condition, or measure the effectiveness of treatment. But they all have some basic truths about what they mean, and how they are best interpreted.

There are two basic kinds of medical test results:

  • Tests that give "yes" or "no" answers (usually for diagnostic purposes)
  • Tests that give relative results (to measure high or low values compared to a "normal" range)

Here is more information about these two kinds of medical tests, and the kinds of questions you'll want answered to better understand what they mean.

Lab tech looking at sample and recording findings
Yuri_Arcurs / Getty Images

Positive and Negative Tests

When you are given a medical test that yields a positive or negative result, you will need to know what the results mean and how trustworthy the test is.

Positive and negative tests are typically used for diagnostic purposes to ascertain whether a disease or condition is present (positive) or not (negative). In layperson's terms:

  • Positive means that whatever the test was looking for was found.
  • Negative means that whatever the test was looking for was not found.

There are also false-positive results in which a disease is detected even if it is not there and false-negative results in which a test fails to detect the disease or condition. Certain tests have limitations and may be less accurate than others.

For example, you may be given an HIV test, and it comes back negative. Because the test detects proteins produced in response to the disease, rather than the disease itself, it may not be able to make an accurate diagnosis if you are tested too soon after HIV exposure.

Other tests have low specificity. What this means is that they may be able to detect certain organisms, but are less able to tell one strain of the organism from another.

Relative Value Tests

Once you have been diagnosed, further testing for that diagnosed problem will usually yield relative results that are important to you.

When you are given a medical test that yields relative results, usually in the form of a number (value), you will want to know what those results mean and how they compare to previous results.

These values can ascertain whether a treatment is working or a disease or condition is progressing. The range of values can sometimes vary based on age, sex, and other factors.

By definition, a relative value test is one that measures specific components of blood, urine, or other lab samples and compares those values to what would be expected in a normal, healthy population.

A complete blood test (CBC) is a prime example of a relative value test. Anything within the range of values is considered normal. Anything above or below the range of values is abnormal.

Abnormal values don't necessarily have diagnostic value but may indicate a developing concern. What is often more important is how values trend between tests, as this can indicate that a treatment is working or failing or if a disease is progressing or resolving.

Questions to ask your healthcare provider about relative tests include:

  • What is normal, and are your results normal?
  • If your results are not normal, are better results higher, or lower, bigger or smaller than the results of your test?
  • What does your doctor recommend you do to bring them into the normal range?
  • How accurate is this test?

Ask for copies of your test results, of course. You might ask for written documentation about where your doctor thinks those relative values should be for you. You might even consider tracking them over time as a way to manage your health.

A Word From Verywell

If your test results are not what you expect, you may want to ask to be tested again. There are many ways mistakes can occur, usually because of errors in collecting, storing, or processing lab samples.

Confirmation of your results will give you more information before you make any medical decisions and will give you confidence in the decisions you make based on those results. If the results can't be confirmed, than you'll know it's time to talk to your doctor about shifting directions.

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  1. nam: aidsmap. False negative results on HIV tests. Updated June 2019.

  2. Plebani M. Diagnostic errors and laboratory medicine - causes and strategiesEJIFCC. 2015;26(1):7–14.