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Interpreting Blood Test Results

written by: Leigh A. Zaykoski•edited by: Paul Arnold•updated: 5/4/2010

While interpreting blood test results for the purposes of medical diagnosis or treatment should be left to medical professionals, gaining a basic understanding of how to read blood tests is important if you want to take an active role in your medical care.

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    Doctors can order blood tests for a variety of reasons. Some of the more common blood tests include BUN (blood urea nitrogen) which helps diagnose kidney problems, BMP (basic metabolic panel) and CBC (complete blood count) as well as the MPV blood test (mean platelet volume). While these may be more common, there are a wide variety of other reasons doctors may order blood drawn, such as the Hgb test to diagnose anemia. Your doctor should explain your symptoms and what he or she is testing for. Proper interpretation of blood test results involves understanding how tests can be affected by the laboratory they are performed at and many other variables. If you are concerned about any of your test results, talk to your doctor or another health care professional.

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    Understanding Reference Ranges

    Most laboratories print a reference range next to each test result listed on your lab report. This helps determine whether your results are normal, low, or high when you are interpreting lab test results. When you're learning how to read blood tests, it's important to know that the reference ranges can vary from one laboratory to another. This is because every lab has a set of procedures that can affect how blood tests are processed. If your result is out of the reference range, it doesn't necessarily mean that something is wrong with you.

    For example, when reading ANA blood test results, high results are indicative of an autoimmune disorder while low are considered normal. However what is considered normal for the ESR test will vary depending on age, gender and medical history. And, of course, there is always the possibility of a false negative, such as in the CA 125 blood test which is only accurate in 50% of cases reporting stage I ovarian cancer. It is important to understand the differences of the tests before interpreting the results. If your doctor suspects a medical condition based on low or high blood test results, you may undergo additional testing to determine if those results are a cause for concern.

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    Lab Report Notations

    Some people get confused when they get their test results back because some results are printed with a footnote or asterisk. If you find this kind of result, look at the bottom of the page and read the footnote associated with that test result. For example, someone who has had renal function tests performed may notice a footnote after their results. The footnote may list the patient's estimated glomerular filtration rate (GFR), which can be calculated using the results of some of the renal function tests. The footnote may also include a reference range so you can compare your result with what is considered normal. Because understanding blood test results with footnotes can be difficult if you don't have medical training, ask your doctor if there is anything you need clarification on or don't understand.

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    False Positives and Negatives

    Without medical training, some people get panicked if they see a high or low blood test result when learning how to read blood tests. However, false positives and negatives can occur with many blood tests because test results can be affected by a wide range of factors. Medications, foods, beverages, and even stress levels can impact your results on a particular day. For instance, estrogen or birth control pills can alter the results of a thyroid lab test.

    The way a lab technician handles your sample can also result in a false positive or negative. For example, potassium is contained within the red blood cells. If a technician handles your specimen too roughly or drops it, the red blood cells could burst. This would result in a high potassium level on your laboratory report. If you get a false result, your doctor may recommend that you have the test repeated. Discuss your lab results with your doctor if you are unsure about interpreting blood test results on your own.

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    Further Information

    Blood Book. "What Does My Blood Test Mean?" Retrieved March 23, 2009.






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