10 Things Your Doctor Won’t Tell You About Your Blood Tests

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4. A “positive” test result may not be positive news

Some blood tests look for diseases by searching for molecular markers in your blood sample — among them the sickle cell anemia test, the HIV test, the hepatitis C test, and the BRCA1 or BRCA2 gene test for breast and ovarian cancer risk. Results are considered “positive” when the test finds the disease marker — DNA or protein — that it is looking for. In these cases, a positive test result means you may have the disease or disorder or that you may have been exposed to it in the past.

5. A “negative” test result is usually good news

Negative is not the same as bad when it comes to blood tests. A negative result means that the test did not detect what it was seeking, whether a disease marker or a risk factor for a health condition. When you’ve had a blood test to check for an infectious disease — a rapid blood test for hepatitis C, for example — getting back a negative result is good news — it means the test found no evidence of an infection.

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