How Accurate Are Pregnancy Blood Tests?

If you're trying to conceive or think you might be pregnant, you may be wondering about pregnancy blood tests. Here, we'll look at the accuracy, benefits, and risks.

People who are trying to conceive may wonder if a blood pregnancy test can be wrong. These tests, which are done at a health care provider's office or in a lab, are over 99% accurate. Blood tests confirm pregnancy by checking for the presence of the hormone human chorionic gonadotropin (hCG), which increases exponentially after conception.

That said, there's still some things to know about pregnancy blood tests. Ahead, learn more about their accuracy, common errors, and reasons to take these types of tests.

what to know about blood pregnancy tests

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Blood Pregnancy Test Accuracy

A urine pregnancy test is just as accurate as a blood test (99%), as long as you wait the recommended amount of time to take it. HCG doubles every couple of days in the very early stages of pregnancy. Urine tests can produce a false negative if the urine is diluted (from over-hydration) or the test is taken too early.

As with home urine tests, it is possible, although rare, to end up with false results (both negative and positive) from a blood pregnancy test.

Can You Get a False Negative on a Blood Pregnancy Test?

A false negative means the test is negative, indicating you are not pregnant, but you actually are pregnant. This result can occur if the blood pregnancy test was performed too early, when there is not enough hCG in the blood to detect a pregnancy.

However, once you reach nine to 14 days pregnant, it's very unlikely to get a false negative result. If you believe that you got a false negative from testing too soon, your doctor may repeat the test after 48 to 72 hours.

Beyond testing too early, a false negative blood test can occur in rare occasions with multiple gestation and/or if there is a condition called gestational trophoblastic disease, also known as molar pregnancy. In this case, the lab will need to dilute the sample before performing the test to get an accurate result.

Can You Get a Negative hCG Blood Test but Be Pregnant?

A false positive test means that the test reads positive—it says you're pregnant—but you're not. This happens very rarely. You may get a false positive if you are taking a medication that contains hCG (such as when undergoing fertility treatments) or due to certain medical issues. Possible causes of a false positive may include:

  • Antibodies present in the blood due to exposure to certain animal products (called heterophile antibodies)
  • Blood or plasma transfusion
  • Taking hCG for weight loss, doping, or fertility
  • Immunoglobulin A (IgA) deficiency
  • Kidney failure
  • Rheumatoid factors
  • Certain types of cancer

Reasons to Take a Blood Pregnancy Test

Blood pregnancy tests are more sensitive than urine tests. They are typically used for those facing infertility, those with a suspected ectopic pregnancy, or a suspected miscarriage.

A blood test can confirm pregnancy as early as 9 days after conception. Urine pregnancy tests take at least 10 days or longer.

Blood pregnancy tests have to be taken at a health care provider's office, hospital lab, or outside lab. The physician might advise you to wait until a missed period to do any type of pregnancy testing so you can get the most accurate result. Testing too early can produce a false negative.

Unlike home pregnancy tests, blood tests don't give immediate results. You'll have to wait for a blood pregnancy test result to come back from the lab.

Qualitative vs. Quantitative Blood Pregnancy Tests

There are two types of blood pregnancy tests, both of which offer highly accurate results.

A qualitative blood serum test confirms whether or not hCG is present in the blood, basically offering a yes (you're pregnant) or a no (you're not pregnant) result. The qualitative hCG blood test is about as accurate as a home urine test.

A quantitative blood serum test is also known as the beta hCG test. It measures the exact amount of hCG in your blood. Because this test can detect even trace amounts of hCG, it is highly accurate. Health care providers use this test, along with ultrasound, to diagnose an early pregnancy loss or ectopic pregnancy.

Drawbacks of Blood Pregnancy Tests

Even though a blood pregnancy test can be performed earlier than a urine test, it can take longer to receive your results. The timing of results varies from lab to lab and can range from an hour to a few days. Also, while it's rare, a blood pregnancy test result can be wrong.

Blood pregnancy tests must be performed in a health care provider's office, taking more time out of your schedule. Blood tests are more expensive than home pregnancy tests (depending on physician and lab fees). Waiting a few extra days to do a home urine test tends to be more convenient.

Possible Risks of a Blood Pregnancy Test

There is very little risk associated with getting a blood pregnancy test. Just as with any blood test, you may feel lightheaded, faint, have excessive bleeding, infection or bruising at the puncture site, and/or hematoma (blood accumulating under the skin).

Since veins and arteries differ in size from one person to another (and from one side of the body to the other), getting a blood sample could be more difficult for some people. In order to get the required blood sample, you might need multiple pricks to locate a vein.

The Bottom Line

Waiting to find out whether or not you're pregnant can feel like it takes an eternity, especially when you're anxious to get the results. If you're having a blood pregnancy test, however, you can feel confident in the results as they are typically 99% (or more) accurate.

It's best to take the advice of medical professionals and avoid testing too soon. Home urine tests or in-office blood testing can give you false information when not performed as directed. If you have concerns or suspect a false negative or false positive, talk to a health care provider about further testing to confirm your results.

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Sources
Parents uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1.  Analysis of human chorionic gonadotropin levels in normal and failing pregnancies [40]Obstet Gynecol.

  2. Pregnancy Tests. Planned Parenthood.

  3. Pregnancy. U.S. Food and Drug Administration. 

  4. Human Chorionic Gonadotropin. National Library of Medicine.

  5. Immunoglobulin A (IgA) Deficiency. Johns Hopkins Medicine.

  6. Early pregnancy loss. American College of Obstetricians and Gynecologists. 

  7. Current applications of therapeutic phlebotomyBlood Transfusion.

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