10 Facts Doctors Don’t Always Tell You About Blood Tests

When you visit your doctor for a regular checkup it's quite standard that blood tests are ordered. This is the normal way for doctors to access your health but most times the results we get look like gibberish. Because tests can be overwhelming it’s important to ask relevant questions. Here are 10 things that you might not know to ask.



1. Standard tests to look out for

A typical set of tests might include a CBC, a complete blood count, which measures hemoglobin, and the number of red and white blood cells in your system. They might also request a basic metabolic panel, also called a blood chemistry, which looks at the chemical levels in your blood such as blood glucose, electrolytes, and calcium to check on your organ function. Another test is called the lipoprotein panel, which looks at the fat levels in your blood, to check cholesterol.

2. Doctors focus on the bad news

Doctors don’t discuss the good news. If your test comes back without any bad results, they tend not to contact you. They might send you the test results without any explanation, which can be difficult for a person who didn’t go to medical school to understand. It’s a good idea to follow up with a nurse practitioner or doctor, even if the results came back without any concerns. It’s good to track if the results differed from your last set of tests and find out what those changes might mean.   

old female doctor giving bad news to female patient

3. Positive and negative are opposites in bloodwork

When it comes to bloodwork, the meanings of these words get reversed. When a test result comes back positive it means the molecular markers in your blood test detected traces of the disease, gene or risk factor, which is not good news. When a test result comes back negative, it means the test did not find anything indicating you have a disease or a disorder. For example, a test looking for DNA markers for the BRCA1 or BRCA2 gene for breast and ovarian cancer risk, you should be hoping for a negative result, indicating you don’t have the gene.

4. Results differ from person to person

It’s never a good idea to compare your results to that of others. For example, what is considered normal for men can be quite different from what normal looks like for women. If you compared the results of red blood cells in a CBC, the results will be much higher for men, with 5 to 6 million cells per microliter, compared to pre-menopause aged women who average 4 to 5 million, due to loss of blood during menstruation.

5. Age affects the results

It’s important to know that results mean different things at different ages, as normal levels change as you age. For hemoglobin, which is part of the CBC test, children’s levels are much lower than adults, ranging from 11 to 13 grams per deciliter (abbreviated to gm/dl). For adult men, it should range from 13.5 to 17.5 gm/dl and women it should range from 12 to 15.5 gm/dl. The difference is notable. Similarly, cholesterol numbers mean vastly different things as you age. LDL (Low-density lipoprotein – the bad kind of cholesterol) levels should be lower than 130 milligrams per deciliters for most people. Rates of 160 to 190 mg/dl indicate a risk for heart disease. The risk is higher if you are over the age of 45 for men and 55 for women.

6. False-positive test results are quite common

Tests sometimes come back positive when they are not, called a false-positive, which means a person might think they carry the markers for a genetic disorder when in fact they do not. The first screening for a condition often needs to be checked with a more specific second test, to determine whether the results are accurate. An example is the rapid HIV test, which is not as reliable as the tests requiring longer waiting periods for the results, which often produces false positives. In communities with a one percent infection rate, for every ten true positive results, two false-positive HIV rapid test results are expected.

7. False negatives test results can also happen

In other cases sometimes a test fails to detect evidence of a disease or condition you actually have. An example is blood tests for hepatitis C, where results come back negative when you were exposed to the virus, and the disease markers lie dormant in your system. If you think you’ve been exposed to an infectious disease, it’s always a good idea to get tested a second time.

8. Mistakes do happen

Although rare, sometimes mix-ups and mistakes do happen. Lab technicians are human and despite strict practices to ensure accurate results, errors can happen. On rare occasions, test samples are switched. Results can also be affected by how blood samples are handled before being analyzed. For instance, if a blood sample is shaken in the tube, the blood cells can burst, releasing their contents, possibly causing the test results to differ.

doctor made a mistake

9. Not all labs are the same

Don’t compare reports from different labs. Lab technicians compare your test results to the range that is considered normal for that laboratory, so their reference is based on the people previously tested in that lab. Sometimes a lab will set their own reference range, or use different equipment or tests, which impacts the results, making one lab’s normal range different to that of another lab’s. Some tests have set a standardized reference range, such as the test for blood sugar and the results are universal.


10. Abnormal results aren’t always an indicator

If you get back a test result outside the normal range of the lab’s expected values leading to a diagnosis. Sometimes this outcome is due to other reasons. For example, if you drank alcohol or ate something before the tests, this could influence the results. That’s why it’s very important to follow the lab’s instructions for tests, such as fasting for cholesterol tests, or drinking water for an ultrasound. If you suspect your outcome was affected by an external source, it’s important to ask to get retested.

h/t: www.everydayhealth.com

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